A Thesis Presented to The Academic Faculty. Peter Riley Exline

Transcription

1 CHARACTERIZATION OF MODIFIED NEUTRON FIELDS WITH AMERICIUM-BERYLLIUM AND CALIFORNIUM-252 SOURCES A Thesis Presented to The Aademi Faulty by Peter Riley Exline In Partial Fulfillment of the Requirements for the Degree Master of Siene in Nulear Engineering Georgia Institute of Tehnology August 2011

2 CHARACTERIZATION OF MODIFIED NEUTRON FIELDS WITH AMERICIUM-BERYLLIUM AND CALIFORNIUM-252 SOURCES Approved by: Dr. Nolan Hertel Woodruff Shool of Mehanial Engineering Georgia Institute of Tehnology Dr. Chris Wang Woodruff Shool of Mehanial Engineering Georgia Institute of Tehnology Dr. Mihael Shannon Defense Threat Redution Ageny United States Military Aademy Date Approved: April 22 nd, 2011

3 To Team Hertel and Team Exline

4 ACKNOWLEDGEMENTS First I would like to thank my ompatriots in Team Hertel, inluding Spener Mikum, Tim Cahill, and MAJ Amy Eastburg. Speial thanks goes to Randi Palmer and Emily Freibert, whose help struturing MCNP odes and organizing my thesis saved ountless hours of work. The experiened hand of Dwayne Blaylok proved invaluable in onfiguring and troubleshooting my detetor setup. The tireless efforts of mahinist extraordinaire Anna MLendon saw 400 pound lead hemispheres lift up in the air and into position. Nazia Zakir s efforts in revising the aess poliy leared my way in. Christina Tabor and Gary Spihiger not only handled many soure movements, but often went well beyond their job requirements and normal work hours to see that the RCZ ran safely. Dr. Chris Wang was the professor who taught my first radiation detetion lass and generated my interest in the field. MAJ Mike Shannon helped me understand the bigger piture of applying my nulear engineering work to the US Army s needs. I d like to thank them both for serving on my thesis ommittee. Dr. Nolan Hertel has served as my mentor. There is none better. Whether I needed resoures, personal MCNP lasses, a volunteer to handle the AmBe soure, or midnight proofreading from Frane, he worked without easing to make me suessful. My wife, Jessia Exline, bore the greatest burdens of all. Without the least omplaint, she juggled all our responsibilities, inluding moving us to another state, while I ompleted this work. I annot thank her enough. Finally, I d like to thank the Lord for all these people and His greatest gift to us. iv

5 TABLE OF CONTENTS ACKNOWLEDGEMENTS... iv LIST OF TABLES... viii LIST OF FIGURES... ix NOMENCLATURE... xi SUMMARY... xiv CHAPTER 1: INTRODUCTION Neutron Detetion Neutron Leakage Spetra Charaterization Proess Overview... 2 CHAPTER 2: EXPERIMENTAL METHODOLOGY AND MATERIALS BSS Detetor System BSS Operating Fundamentals Experimental BSS Equipment Setup Data Colletion Proedure Soures Cf Soure AmBe Soure Moderators Beryllium Sphere Lead Sphere Iron Sphere Tantalum Sphere Polyethylene Sphere Heavy Water Sphere ESJ Method with Axton Corretion v

6 2.5 Unfolding with BUNKIUT and BUMS CHAPTER 3: COMPUTATIONAL MODELS MCNP Code MCNP Input Files MCNP Output and Normalization to Experimental Results CHAPTER 4: RESULTS Total Fluene ICRP 74 Ambient Dose Equivalent H*(10) Neutron Fluene Spetra Beryllium Sphere Lead Sphere Iron Sphere Tantalum Sphere Bare Soure Cf in Polyethylene Cf in Heavy Water CHAPTER 5: CONCLUSION CHAPTER 6: FUTURE WORK APPENDIX A: STARTING SPECTRA FOR ITERATIVE UNFOLDING A Cf in Be Starting Spetrum A Cf in Pb Starting Spetrum A Cf in Fe Starting Spetrum A Cf in Ta Starting Spetrum A Cf in Polyethylene Starting Spetrum A.6 AmBe in Be Starting Spetrum A.7 AmBe in Pb Starting Spetrum A.8 AmBe in Fe Starting Spetrum vi

7 A.9 AmBe in Ta Starting Spetrum APPENDIX B: MCNP INPUT FILES B Cf Bare MCNP Input B Cf in Beryllium MCNP Input B Cf in Lead MCNP Input B Cf in Iron MCNP Input B Cf in Tantalum MCNP Input B Cf in Polyethylene MCNP Input B Cf in D 2 O MCNP Input B.8 AmBe Bare MCNP Input B.9 AmBe in Beryllium MCNP Input B.10 AmBe in Lead MCNP Input B.11 AmBe in Iron MCNP Input B.12 AmBe in Tantalum MCNP Input APPENDIX C: COMPARISON OF 252 Cf SOURCE SPECTRA WITH AND WITHOUT STYROFOAM SPHERE APPENDIX D: ISO 8529 NEUTRON FLUENCE SPECTRA FOR SOURCES APPENDIX E: SAMPLE BUMS OUTPUT WITH REMARKS APPENDIX F: SAMPLE OUTPUT TALLIES F.1 Sample F2 (Neutron Fluene) Tally F.2 Sample F12 (ICRP 74 ambient dose equivalent H*(10)) Tally F.3 Sample F15 (Ring detetor in y diretion) Tally APPENDIX G: MODERATED SPECTRA PLOTTED AGAINST BARE SOURCE SPECTRA REFERENCES vii

8 LIST OF TABLES Table List of Equipment... 8 Table Composition of Iron Sphere Table MCNP Universal Input Parameters Table Total Fluene Rate Comparison Table ICRP 74 Ambient Dose Equivalent H*(10) Table D.1. Values of neutron fluene at 1 meter per logarithmi energy interval for a 252 Cf spontaneous fission soure (derived from Table A.1 of referene [22]) Table D.2. Values of neutron fluene at1 meter per logarithmi energy interval for an AmBe (α, n) soure (derived from Table A.1 of referene [22]) viii

9 LIST OF FIGURES Figure Neutron Leakage Spetra Charaterization Proess Overview... 4 Figure BUMS User Interfae Figure Cf / Beryllium Sphere Spetra Figure AmBe / Beryllium Sphere Spetra Figure Cf / Lead Sphere Spetra Figure AmBe / Lead Sphere Spetra Figure Cf / Iron Sphere Spetra Figure AmBe / Iron Sphere Spetra Figure Cf / Tantalum Sphere Spetra Figure AmBe / Tantalum Sphere Spetra Figure Cf Bare Spetra Figure AmBe Bare Spetra Figure Cf / Polyethylene Spetra Figure Cf / Heavy Water Spetra Figure C.1. Comparison of 252 Cf Soure Spetra from MCNP with and without Styrofoam Sphere Figure E.1. Sample BUMS output with remarks Figure G.1. All 252 Cf Spetra, normalized by total flux Figure G Cf in Beryllium and bare soure Spetra, normalized by total flux Figure G Cf in Iron and bare soure Spetra, normalized by total flux Figure G Cf in Lead and bare soure Spetra, normalized by total flux Figure G Cf in Tantalum and bare soure Spetra, normalized by total flux Figure G Cf in Heavy Water and bare soure Spetra, normalized by total flux 145 ix

10 Figure G Cf in Polyethylene and bare soure Spetra, normalized by total flux. 145 Figure G.2. All AmBe Spetra, normalized by total flux Figure G.2.1. AmBe in Beryllium and bare soure Spetra, normalized by total flux Figure G.2.2. AmBe in Iron and bare soure Spetra, normalized by total flux Figure G.2.3. AmBe in Lead and bare soure Spetra, normalized by total flux x

11 NOMENCLATURE 252 Cf Californium isotope 252 AmBe BSS BUNKI BUNKIUT BUMS D 2 O ESJ MCA MCNP ROI SNM Ameriium-Beryllium Bonner Sphere System US Naval Researh Laboratory Code for unfolding spetra Unfolding ode based on BUNKI Bonner sphere Unfolding Made Simple Deuterium ( 2 H) dioxide (heavy water) Eisenhauer, Shwartz and Johnson model Multihannel Analyzer Monte Carlo N-Partile ode Region of Interest Speial Nulear Materials xi

12 SUMMARY There are a variety of uses for referene neutron fields inluding detetor response and dosimeter studies. The Georgia Institute of Tehnology has a 252 Cf spontaneous fission soure and an AmBe (α, n) soure available for use in its researh programs. In addition, it has iron, lead, beryllium, tantalum, heavy water, and polyethylene spheres to modify the neutron energy distributions from these neutron soures. This researh haraterized the neutron leakage spetra from the soure inside spherial shells using a Bonner sphere spetrometer. All the neutron fields measured were also omputed with a Monte Carlo ode to determine the neutron fluene rate and ambient dose equivalent rate. The omparison of experimental data and alulations are used to provide further insight into the neutron spetra as modified by the spheres. The haraterization of these modified soures will provide data to assist in using the resulting neutron fields in other researh ativities. To measure eah neutron field ombination, one of the two soures was plaed in the enter of an attenuating sphere. The neutron field was first measured at a variety of soure-to-detetor distanes with a Bonner Sphere System. The spetrometer measurements, speifially the ount rates of the different Bonner spheres, as a funtion of distane from the soure is fitted to obtain orretions for room-satter and air-satter of neutrons using the Eisenhauer, Shwartz, and Johnson method. Using these orretions, the ount rates free of room return is obtained at 1 m from the soure and unfolded using the BUMS software to obtain the reported fluene and dose equivalent rates. xiv

13 These results are ompared to those generated by the Monte Carlo Neutral Partile (MCNP) ode. Models were made in MCNP for eah of the soure and moderating sphere ombinations. The neutron fluene and dose rates were tallied during the MCNP simulation. The unfolded experimental data and the MCNP alulations showed good agreement for most of soure-attenuating sphere ombinations, thereby reinforing the experimental results. xv

14 CHAPTER 1: INTRODUCTION The haraterization of neutron fields ontinues to be needed for nulear failities for a variety of appliations. More reently, the possibilities of rogue nations or non-state ators aquiring nulear weapons tehnology and material for use in nulear terrorism have plaed emphasis on the ability to detet speial nulear material (SNM). SNM inlude uranium-233 and -235 and plutonium isotopes [1]. These fissile materials are weapons apable when suffiiently enrihed and obtaining them is the most diffiult task faing potential nulear terrorists [2]. These SNM are radioative, releasing radiation that an be deteted, allowing for material monitoring and interdition. Part of this radiation omes from gamma rays, whih are detetable, but are also easy to shield with high-z elements inluding lead [3]. Some isotopes emit neutrons, whih are not readily shielded by the same materials, and also are not emitted by many of the non-snm radioative materials that would be false positives for a detetion operation. Additionally, SNM an be atively interrogated to release neutrons via reations. Neutron detetors an thus serve as ideal SNM detetion andidates. 1.1 Neutron Detetion The detetion of neutrons relies on reations that release harged partiles like alpha partiles or reoil partiles from sattering [4]. The harged partile reations prinipally used for thermal neutron detetion inlude the 10 B(n, α), 6 Li(n, α), and 3 He(n, α) reations. The most effetive systems for deteting thermal neutrons use the helium-3 1

15 reation. Unfortunately, the supply of helium-3 is urrently very sare [5]. Alternative systems in development inlude lithium and boron oated sintillator detetors. Testing new detetor materials and designs requires known neutron fields. Ameriium-beryllium (n, α) and alifornium-252 (spontaneous fission) are two ommonly used laboratory soures of neutrons. Both soures have been extensively haraterized [6, 7]. It should be noted that AmBe soure fields are dependent on the geometry and omposition of the soures. In order to generate additional neutron fields, partiularly to simulate softer fields that are found in most workplaes, the soures an be plaed inside of shielding/attenuating materials to hange the magnitude and energy dependene of their fluene spetra. Common shielding materials inluding tantalum, beryllium, polyethylene and lead previously have been studied using soures and the resultant spetra measured and omputed [6]. The neutron leakage spetra generated with suh soures inside spherial shells of materials depends on the soure energy distribution, the shielding/attenuating sphere, room and air satter, and geometri onfiguration. This thesis researh seeks to haraterize the neutron fields resulting from bare AmBe and 252 Cf soures and the fields produed when they are plaed inside spherial shells of shielding/attenuating materials available at the Georgia Institute of Tehnology, in partiular lead, steel, beryllium, tantalum, polyethylene, and heavy water spheres. 1.2 Neutron Leakage Spetra Charaterization Proess Overview Charaterizing the neutron fields requires measurement of the neutron spetra and an be supplemented by simulating the spetra with neutron transport odes. The 2

16 experimental and alulated results are then ompared for onsisteny and the fields haraterized for further researh appliations. To experimentally measure the neutron field for eah soure-attenuator ombination, measurements were made with a BSS at a variety of distanes (Chapter 2.1). For eah shielding/attenuating material, one of the two soures (Chapter 2.2) was plaed in the enter of one of the attenuating spheres (Chapter 2.3). Count rates are reorded for eah of the BSS detetor systems at several distanes from the soure enter. Corretions for room satter and air satter of neutrons are then made using the ESJ model (Chapter 2.4). The Axton method is used to orret ount rates for the geometry of the system. After these orretions, the ount rate data an be unfolded to reonstrut a neutron spetrum using the BUMS software (Chapter 2.5). The resulting fluene and dose equivalent rates are then reported. These results are ompared to those generated by the MCNP simulations (Chapter 3.1). Models were made in MCNP for eah of the soure and attenuating sphere ombinations (Chapter 3.2). The models were exeuted and neutron fluene and dose measurements were tallied and normalized to the neutron soure strengths and ompared to the BUMS output (Chapter 3.3). The unfolded experimental data and the MCNP alulations are then analyzed and heked for onsisteny, whih would lend onfidene to the results (Chapter 4.1). The results were then used to reate new starting spetra for BUMS that reflet the new neutron fields that an be generated at Georgia Teh (Chapter 4.2 and Appendix A). The MCNP models were also refined and doumented to allow future researhers to modify 3

17 and use them in further work with these haraterized neutron fields (Appendix B). The proess is summarized in Figure below.. Figure Neutron Leakage Spetra Charaterization Proess Overview 4

18 CHAPTER 2: EXPERIMENTAL METHODOLOGY AND MATERIALS In this hapter, the measurement portion of this researh is developed, inluding equipment setup, materials studied, experimental proedures, and analysis proedures for taking olleted raw data and generating flux, dose, and neutron energy spetra. 2.1 BSS Detetor System BSS Operating Fundamentals The BSS was first designed in 1960 by Bramblett, Ewing and Bonner at Rie University [7]. The system is named for one of the prinipal reators, T. W. Bonner. The priniple of operation is to plae a thermal neutron detetor at the enter of a moderating sphere that ould be easily hanged to a variety of sizes to obtain different energy sensitivities. By varying the amount of moderation an inoming neutron field experienes before interating with the detetor, the detetor ould be made sensitive to different energy ranges, inluding those too high for it to effiiently detet otherwise [8]. For this experiment, a BSS set manufatured by Ludlum, model 42-5 [9], is used. It inludes a 4mm x 4mm Ø LiI(Eu) sintillator detetor and 2, 3, 5, 8, 10, and 12 diameter polyethylene moderating spheres. The relative ount rate per unit fluene versus neutron energy level is shown in Figure

19 Counts-m2 1.E+00 1.E-01 1.E-02 1.E-03 BARE CD COV 1.E-04 2 IN 3 IN 5 IN 8 IN 10 IN 12 IN 18 IN 1.E-05 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 Energy (ev) Figure Count Rates per Unit Fluene of Different Bonner Spheres [10] In Figure , it is shown that several of the moderated detetors peak at higher energies and others at lower energies. A weakness of the BSS is that none of the moderator responses have strong struture in the intermediate energy range, whih limits energy resolution in this area [11]. The details of going from raw ount rates to neutron fluene spetra, also known as unfolding, will be overed later in this hapter Experimental BSS Equipment Setup In addition to the Ludlum model 42-5 BSS equipment, other eletronis and software were needed to apture neutron ount rates for the experiment. To minimize dose to the operators, the detetor was plaed on the far side of a shielding wall in the Radiation Control Zone IC area of the Neely Nulear Researh Center at the Georgia 6

20 Institute of Tehnology. Wires were run through onduits to the preamplifier and detetor, while the remainder of the equipment remained on the other side of the shielding wall. The shielding wall onsisted of onrete bloks and a sheet of 1 borated polyethylene. The power and signal flow is summarized in Figure , and the detetor room setup is shown in Figure The list of equipment is in Table (Note that the exat loation of the soure sometimes varied due to limitations on the overhead rane s travel range when lifting the heavier attenuating/shielding spheres into position. These differenes are aounted for in the measurement proess. Regardless of rane limitations, no soure or detetor loation was within 1 meter of sattering surfae other than their own supports.) 7

21 Figure Signal and Power Flow of BSS Table List of Equipment Type Manufaturer Model Serial Number Detetor Ludlum 42-5 A PR Pre-Amplifier Orte 142 n/a HV Power Supply Orte Amplifier Orte 571 n/a NIM bin Orte 4001A/4002A 4133, rev. 31 MCA ard TRUMP PTRU PC Dell Vostro 200 FKQZRH1 Software Orte Maestro.32 n/a 8

22 Figure Overview of Detetion Room [12] Data Colletion Proedure For eah soure and attenuator ombination, data were olleted for eah of the Bonner spheres at seven different soure-detetor distanes. Establishing seven data points for eah setup allows for later room sattering and air sattering orretions to be made. The distanes were seleted with the goal of finding a orreted ount rate for a one meter distane, so distanes loser and farther this distane were piked. The lower distane limit was set by the dead time experiened by the detetor with the Bonner sphere having the highest ount rate for that soure/moderator ombination and in no 9

23 ase was loser to the soure than 40 m measured from the enter of both the detetor and soure. Dead time was not allowed to exeed 4%. For eah measurement, integral ounts for the neutron-indued peak were reorded. Setting a ROI about the neutron-indued peak allowed the MAESTRO software to perform a gamma ray bakground subtration. This MCA software was also onfigured to stop olletion when 10,000 net ounts were made in the ROI enompassing the peak. The live time needed to reah this threshold was then reorded and divided into the final number of ounts to determine the ount rate. Figure Sample Spetrum Analysis from MAESTRO MCA software. The ROI about the alpha peak is shown in red. Note that the software gives the net ounts for the ROI and reports an assoiated error. Figure above shows the spetrum result in MAESTRO for the bare AmBe soure measured with a 5 Bonner sphere at a soure-detetor distane of 1.5m. The box 10

24 at the top of the ROI shows the gross and net integrated ounts, and an estimation of error. This estimation of error is based on MAESTRO s interpretation of the bakground ounts. MAESTRO determines this by taking the average of the first three hannels of the ROI and the last three hannels of the ROI, and applying the trapezoidal rule in between them. This figure is then subtrated from the gross ounts to get the net ounts, and an assoiated error. This leads to some nuanes in properly seleting the ROI for eah spetrum. When the overall bakground is low, MAESTRO s error estimation beomes very sensitive to the exat hannels seleted for the edges of the ROI. A hange of 10 hannels (out of 8192 being reorded) an result in the error estimate varying more than 50% and vary the net ounts up to 10%. This is due to even a small bakground undulation in the first or last three hannels having a disproportionate effet on the alulation. To reate onsistent results, it is neessary to selet an ROI slightly larger than the strit peak area, and to ensure that both boundaries lay in onsistent bakground areas (not near small spikes in bakground). The larger ROI does not signifiantly inrease the ounts measured, but greatly inreases onsisteny in measurement. Just as bakground small spikes an inrease error, seleting unusually low bakground areas for bounds resulted in signifiant underreporting of error. For onsisteny, errors less than 180 ounts (1.8%) or greater than 360 ounts (3.6%) triggered a reevaluation of the ROI for small spikes or dead spaes in the bakground. In every ase, the bakground error ould be inreased above 180, and in almost every ase, redued below 360. The only exeptions were when the bakgrounds ounts were 11

25 legitimately high ompared to normal, whih ourred most often when the detetor was used without a moderating sphere (a bare detetor measurement). After an appropriate ROI had been determined, the following data were reorded: soure/attenuator ombination, date, time of measurement start, soure-detetor distane, Bonner sphere used, lowest ROI hannel, highest ROI hannel, gross ounts, net ounts, MAESTRO-reported error, detetor live time, and total time. The aptured pulse-height file was also saved to the PC to allow later review and ROI adjustment if needed. This proedure was repeated for all six Bonner spheres and the bare detetor for eah soure-detetor distane. Data sets for seven different soure-detetor distanes were reorded for eah soure-moderator ombination. These 49 ount rate data points beame the starting point for the unfolding proess overed in Chapter Soures The experiments were onduted with two soures, 252 Cf and AmBe Cf Soure The 252 Cf soure emits neutrons by spontaneous fission. It has an effetive halflife of years, with a spontaneous fission half-life of 85.5 years. The enapsulation is illustrated in Figure The enapsulated soure has an outer radius of 0.47 m and a length of 3.76 m, not inluding the small stem attahed for safer handling. The ISO standard neutron fluene spetrum from this soure is available in Appendix D. On 12/31/2010, the soure mass was µg, giving a soure strength of 3.03 x 10 7 neutrons/seond based on an emission rate of x 10 6 per seond per mirogram of 12

26 Cf-252 [13]. Soure strength adjustment for radioative deay and soure anisotropy are disussed later in this hapter. The soure is modeled in MCNP using a Maxwellian distribution with temperature of 1.42 MeV. Figure Enapsulation of 252 Cf Soure Two diffiulties were enountered in using this soure. First, its ylindrial geometry had to be adapted for entering in some of the attenuating spheres that had spherial soure avities. The soure was positioned in the spherial avities by inserting it into a styrofoam ball (diameter = 6.1 m) with a hole ut into it to fit the 252 Cf soure. Styrofoam was assumed to be of suffiiently low density as to not be inluded in the neutron transport alulations [14]. This premise was tested with MCNP by plaing the 252 Cf soure in a Styrofoam sphere and omparing the results to the bare soure. The 13

27 validation of this premise an be seen in Appendix D. The seond issue was that the stem, originally designed to unsrew from the soure, ould not be unsrewed for measurements. This aused the experimental setups to need adjustment to aommodate the metal stem, thereby reduing the spherial symmetry. The soure/sphere systems were modeled inluding that asymmetry and it is disussed in the setions on the attenuator/shielding setions. Most notably this oasionally fored the 252 Cf soure into a horizontal orientation rather than the preferred vertial orientation pitured in Figure The resulting anisotropy effet was aounted for by the modeling of the atual measurement geometry AmBe Soure The AmBe soure emits neutrons via the 9 Be(α, n) 12 C reation using the MeV alpha partiles emitted by 241 Am. 241 Am has a half-life of years, so no deay orretion is needed for the measurement period. The AmBe soure is a spherial soure that was first used at NASA to do shielding studies [6]. The soure onstrution is illustrated in Figure (A non-radioative replia of the soure is pitured on the left, to minimize dose during photography.) 14

28 Figure Enapsulation of AmBe Soure. The enapsulated soure has an outer radius of 3.05 m not inluding the small srew attahed for safer handling at the top of the soure. The ISO referene neutron spetrum for AmBe is in Appendix D. The soure strength was first onstruted in January, 1966 and when deayed to the experimental period, the soure strength is 1.2 x 10 8 neutrons/seond [15]. The soure is modeled in MCNP using the energy distributions provided by the NASA manual [15]. The AmBe soure fit several of the moderator geometries perfetly as they were originally designed for use with it [6] and its srew is detahable, greatly reduing some of the diffiulties faed when plaing the 252 Cf soure with its stem attahed. However, the AmBe soure presents a higher dose rate when handling, requiring areful planning to redue exposure during soure movements [16]. 15

29 2.3 Moderators Using the two soures as bare soures and the attenuating/shielding spheres, a total of 12 unique neutron fields (inluding eah soure without moderation) an be generated. The spheres used to alter the Cf-252 and AmBe soure spetra are beryllium, lead, iron, tantalum, polyethylene, and heavy water. (Due to geometri onstraints, i.e. the absene of a spherial avity in the enter, only the 252 Cf soure ould be plaed in the last two aforementioned moderators.) Beryllium Sphere The beryllium sphere was seleted beause beryllium is a neutron multiplier, having a signifiant (n, 2n) reation. The (n, 2n) reation reation threshold is 2.3 MeV [17]. Sine a greater fration of the AmBe neutrons are above this energy and the soure strength is higher, more multipliation will our for the AmBe soure than the Cf-252 soure. In either ase, this will result in larger magnitude neutron fluene from the same soures, albeit at possibly lower energy levels due to sattering and absorption. A photograph of the Be sphere and its MCNP model with the different soures in it are pitured in Figure

30 Figure Beryllium Sphere and MCNP Models. The turquoise piee is the aluminum mounting stand and an aluminum ring to keep the sphere from rolling. The beryllium sphere is mahined into two hemispheres that lok together tightly. It also has a removable plug (pitured in Figure ) that has a onentri smaller removable plug (not pitured, but depited in the MCNP diagram.) Due to the inability to remove the stem of the 252 Cf soure, this smaller plug had to be removed from the beryllium sphere for that measurement set, and was appropriately modeled in MCNP. The beryllium sphere is not exessively heavy, but did require handling with are due to the toxiity of the metal. The sphere was plaed on an aluminum table for measurements, also shown at the bottom of the MCNP model Lead Sphere The lead sphere available at Georgia Teh is inhes ( m) in diameter. It is of interest when designing detetors attempting to trak SNM, as lead is a likely gamma ray shielding hoie for smugglers. Its large atomi number results in little 17

31 slowing down of neutrons per satter. It has an (n, 2n) threshold of about 11 MeV. The sphere and its MCNP model are pitured in Figure below. Figure Lead Sphere and MCNP Model. The lead sphere was manufatured as two hemispheres that lay on eah other without interloking. There is a avity in the enter sized orretly for the AmBe soure or the styrofoam-mounted 252 Cf soure. Pitured and modeled above is the situation aused by the 252 Cf soure s stem. The detetor was plaed in the opposite diretion from the opening aused by the stem to minimize impat of the air gap, but the gap was modeled in MCNP. (The AmBe soure aused no issues in losing the sphere orretly.) The lead sphere weighs over 800 pounds, and proved hallenging to lift into plae on the aluminum table. The top of the sphere had a onvenient removable plug that ould be replaed by a steel bar to lift with, but the bottom half had no suh plae to lift from. 18

32 A mahinist had to reate a lifting assembling for use with the rane to move this into position. The assembly was removable one the lead sphere was in position Iron Sphere The iron sphere, stritly speaking, was made of steel, and had low onentrations of arbon, manganese, phosphor and sulfur [18]. It did onsist of over 99% iron and thus retained its moniker. (The atual omposition was refleted in MCNP and is shown in Table ) The overall radius of the sphere is 38.1 m, although the sphere is made of trunated onial setions whih approximate a sphere. The sphere and its MCNP model are pitured in Figure Figure Iron Sphere and MCNP Model (top-down view on right) 19

33 Table Composition of Iron Sphere Composition of Iron Sphere Element Weight % Iron Carbon 0.21 Manganese 0.47 Phosphor Sulfur The iron sphere was mahined as one solid piee onstruted out of multiple sandwihed layers. There are four different ports for inserting soures or detetors; all but the one pitured were ompletely plugged with iron. The entral avity was designed for larger soures than those used, atually to aommodate an aelerator drift tube and target. A styrofoam support struture was used for both soures. Pitured in Figure is the displaement of the final plug aused by the 252 Cf s stem. This stem also fored the horizontal soure orientation in this sphere. Both are modeled in MCNP. To minimize dose while handling the AmBe in this onfiguration, the srew and ord were left on, reating a slight displaement in the left plug, whih was also modeled. The iron sphere weighs over 3000 pounds and required a onrete blok stand to be onstruted. It did ome with its own steel support struture (painted orange in Figure ) Tantalum Sphere The tantalum sphere was seleted beause, when initially modeled in MCNP, it appeared to shift the neutron fluene spetrum to lower energies while reduing overall 20

34 fluene by only 25%. This should be a good test of the analysis in the MeV range. The sphere and its MCNP model are pitured in Figure Figure Tantalum Sphere and MCNP Model and the lifting devie whih was left on during the measurements. The tantalum sphere has a density of g/m 3 so this 12 m radius sphere proved diffiult to lift. Like the lead sphere, it onsisted of two non-interloking hemispheres with a avity that fit the AmBe soure and styrofoam-mounted 252 Cf soure. The hemispheres eah had small grooves near their equator that ould be used to grip for lifting. The bottom sphere was able to be lifted onto the aluminum table with the rane using a wide nylon strap. The top sphere, laking the lifting point provided on the lead sphere, required an elaborate aluminum attahment to be mahined and attahed. In order to redue reeived dose for the experimenters, it was deided to leave this aluminum attahment in plae for the duration of the measurements and model it in MCNP. 21

35 The 252 Cf s stem only aused very minor hemisphere displaement in this setup, as the end of the stem (whih is thiker than the rest of the stem) resided outside the bak of the sphere Polyethylene Sphere The polyethylene sphere was seleted beause its neutron sattering properties are well-known and ould be used to ompare experimental results to established data. The sphere and its MCNP model are pitured in Figure The sphere is m in radius and did not prove espeially diffiult to mount on its aluminum stand or to model. Sine it is onstruted out of one solid piee of material with a hole drilled for only a small soure, the AmBe soure ould not be used with this moderator. The stand was not inluded in the omputation. Figure Polyethylene Sphere and MCNP Model 22

36 2.3.6 Heavy Water Sphere The heavy water sphere was seleted beause it is a standard for alibrating dosimeters and neutron survey instruments [19, 20]. Sine the spetrum from this sphere has a substantial number of neutrons below 1 MeV, it is used to alibrate neutron instruments for use in nulear reator failities. The sphere and its MCNP model are pitured in Figure Figure Heavy Water Sphere and MCNP Model The heavy water portion of the sphere is 15 m in radius and is ontained in a thin stainless steel shell 0.08 m thik. The moderator also omes with a thin, removable admium over 0.05m thik, whih was left in plae. This removed neutrons with energies below the admium utoff of ev. Like the polyethylene sphere, its 23

37 avity was not large enough to use with the AmBe soure, but otherwise it proved to have no diffiulties in mounting on its aluminum stand or in modeling. 2.4 ESJ Method with Axton Corretion Unfolding the raw ount rate data into a neutron fluene spetrum requires orretions for room sattering, air sattering, and the geometries between the soure and detetor. A proven tehnique involves performing a modifiation for geometry of the system, then applying a least-squares fit to solve for the sattering orretions. This tehnique is known as the ESJ fitting method with the Axton orretion. The disussion of this tehnique below is derived diretly from the works of J. B. Hunt [21] and J. E. Sweezy, et al. [22]. Note that sine the MCNP model inludes air satter, the ESJ method was followed but with setting air satter oeffiients to zero. In an ideal measurement room of infinite dimensions, a perfet vauum, and using a soure and detetor ombination that required no supporting strutures, there would be no room-satter or air-satter. The dead-time orreted ount rate of the detetor, C, would be inversely proportional to the square of the soure-detetor distane, D for a point soure. The produt of these two, CD 2, is known as the harateristi onstant, and follows the inverse-square law. In realisti measurement rooms of smaller dimensions, room and air satter must be aounted for, and signifiant modifiation of the original relationship is required. Aounting for the soure s anisotropy, room-satter, and air-satter yields: 24

38 ( ) ( ) ( ) ( ) where D is the soure-detetor distane, F I is the soure anisotropy orretion fator, F 1 (D) is the orretion for the non-uniform illumination of the detetor, F 2 (D) is the air and room sattering orretion fator, R is the radius of the spherial detetor (inluding any Bonner sphere on it), and K is the satter-free detetor response at a unit distane from the soure in a vauum. The soure anisotropy fator is speifi to eah soure design, and is a funtion of the angle between the soure orientation and the line-of-sight to the detetor. It an be asertained experimentally or modeled. In this researh, values of anisotropy from manufaturer s data and previous researh were obtained [23], but sine the geometry and orientation of the soure ould be modeled in MNCP, this orretion was not needed. The need for the F 1 (D) geometri orretion fator was shown by E. J. Axton [24]. The orretion is due to the divergent, non-parallel beams oming from a soure impating a muh larger detetor sphere at a lose soure-detetor distane D. J. B. Hunt derived an exat expression for this fator from Axton s theory [20]: ( ) { [ ( ) ] } D o is the effetive enter distane between the soure and detetor enter, and is generally lose to D + R. δ is an empirial fator aounting for the relative effetiveness of the extra neutrons present in a divergent beam above what would be expeted from a 25

39 parallel beam, and a value of 2/3 is generally aepted. This Axton orretion is used orreting ount rates in this researh, and was largest when the 12 Bonner sphere was nearest the soure. There are several tehniques for evaluating the F 2 (D) sattering orretion fator. The ESJ model assumes that the air sattering omponent is very small, and evaluates the F 2 (D) as: ( ) ( )( ) S is the room-sattered omponent, and A is the air-sattered omponent (set to zero for this researh as the air satter is modeled in MCNP and does not need orreting for omparison). Substituting into the original C(D) equation yields: ( ) ( )( )( ) ( ) ( ) ( )( )( ) ( ) ( )( ) ( ) Defining C 1 (D) as the anisotropi, geometri, and air-sattered orreted ount rate on the left hand side of the equation yields: 26

40 ( ) ( ) This form of the equation an be solved using a linear least-squares fitting tehnique to find values for K 1 and S. Sine some of these fators vary with the size of the Bonner sphere (whih affets the detetor radius R), the fit is done independently for eah Bonner sphere size within a soure/moderator ombination. There are data points refleting seven different D s for eah Bonner sphere in the measurement set. A orreted ount rate is thus obtained for eah Bonner sphere at a unit distane (1 meter) for eah soure/moderator ombination. This ount rate data is now ready to be unfolded into a neutron spetrum. 2.5 Unfolding with BUNKIUT and BUMS Unfolding the raw ount rate data into a neutron fluene spetrum requires knowledge of the response of eah Bonner sphere to a given neutron spetrum. The disussion of this unfolding proess losely follows that given by E. A. Burgett [25]. The ount rate of eah sphere is related to the response funtion and neutron spetrum through the following first order Fredholm integral equation: ( ) ( ) where C i is the ount rate of the ith Bonner sphere, R i (E) is the response funtion for the ith detetor at energy E, and φ(e) is the energy-dependent neutron flux. 27

41 To solve this equation, it is redued into disrete groups reated by energy bins. This allows the equation to be written in matrix form: where g represents eah energy group, G represents the highest energy group, R i,g is the response funtion of the ith detetor in the gth energy group, and φ g is the group flux between E g and E g-1. To reate a desriptive spetrum, it is desired to have a large number of energy groups G, often in exess of the number of detetors (Bonner spheres) I. This results in a matrix equation that is underdetermined, lending itself to an iterative solution. To get physially meaningful results, a good seletion for the initial starting spetrum is important for the iterative proess. The BUMS system designed by J. E. Sweezy et al. integrates multiple omputer iterative unfolding odes, inluding SPUNIT, BON, MAXED and SAND-II [26]. It aepts inputted ount rates from a BSS, and allows the user to set various parameters, inluding seleting the starting spetrum, unfolding method, and unfolding matrix. The user interfae is shown in Figure below. 28

42 Figure BUMS User Interfae The BUMS system features an automati searh option for the starting spetrum, whih runs the input ount rates against all the available starting spetra and determines whih fit gives the least amount of error. This option was used for soure/moderator ombinations that had known spetrum in BUMS, and resulted in the orret seletion of the starting spetrum eah time. This inluded both bare soures and the 252 Cf in the D 2 O 29

43 moderator. For the ombinations that laked a known baseline spetrum in BUMS, the MAXIET algorithm was used in lieu of a set starting spetrum. This algorithm reates a starting spetrum based on the input ount rates, and assumes a general shape with a high-energy Maxwellian peak, a (1/E) x intermediate energy omponent, and a thermal peak. The algorithm iterates to fit these parameters to arrive at a starting spetrum whih seeds the iterative proess that yields an unfolded spetrum for the input ount rates [26]. The BUMS system outputs a large amount of information based on the fluene, inluding the fluene per unit lethargy as a funtion of energy and the average error in the ball ounts (a funtion of the differene between the measured and alulated ball ounts). It also provides the total fluene and a variety of dose equivalent quantities inluding the ICRP-74 ambient dose equivalent H*(10) values. The table and these two values are used in the omparison to both known spetrums and values, and the MCNP alulations, to evaluate the validity of the experimental proess and to generate new starting spetra for BUMS. A sample of the BUMS output with omments showing whih data are used for this analysis is available in Appendix E. 30

44 CHAPTER 3: COMPUTATIONAL MODELS Computational modeling and simulation an be used to generate omplementary information about experimental proedures and results while simultaneously allowing for perturbation of testing parameters to see hanges in results without onduting additional time-onsuming or expensive experiments. Consisteny between known values, experimental data, and omputational model output is neessary for the latter to be a reliable tool in the researh proess. A goal of this researh is to produe both valid neutron energy spetra and baseline omputational input odes for the soure/moderator ombinations being haraterized. These spetra and odes an provide starting data for further researh using these moderated neutron fields. 3.1 MCNP Code The MCNP ode was developed by Los Alamos National Laboratory uses the Monte Carlo method to simulate the propagation of partiles, inluding neutrons and photons [27]. It is able to integrate the latest ross-setional data for simulation and an generate output based on user-defined tallies. The soure and moderator geometries and omposition, along with the desired tally sheme, are reated in an MCNP input file. The input files designed for the new soure/moderator ombinations being haraterized will, when validated, be outputs of this researh and useful to future work with these neutron fields. This researh used MCNP 5 version All input files were reated using a text editor, but ould be visualized and heked for geometri onsisteny using the inluded 31

45 VISED X_22S visual editor [28]. This release of MCNP 5 also inluded ompiled Windows binaries inluding an exeutable apable of multithreading (mnp5_threads.exe). This greatly redued omputational time when using high-end desktop mahines with six ore proessors. 3.2 MCNP Input Files The MCNP input files reated used some universal parameters that are summarized in Table below. The omplete input files are available in Appendix B. Table MCNP Universal Input Parameters Parameter Value Comment Number of partiles 1 x 10 7 Point of diminished return on error redution for these models Tally sphere radius 100 m Enlosed all models and allowed for diret omparison of fluene spetra with BUMS output Energy Cutoff for neutrons 1 x ev Redued omputational load for partiles below thermal energy threshold and beyond energy resolution of experimental setup Energy Cutoff for photons 1 x 10-2 ev Redued omputational load for photons that had little effet on alulated dose rates Composition of Air Simulated air onsisted of 75.58% N, 23.14% O, and 1.28% Ar by weight The tallies used for this researh inlude an F2 neutron surfae rossing tally olleted on a 100 m sphere, and subdivided into 10 regions eah subtending an equal solid angle. Also tallied was the ICRP 74 dose equivalene for neutrons on the same 32

46 tally surfae. Finally, for soure/moderator ombinations with signifiant geometri asymmetries, a point detetor was used at 100 m in the diretion where the atual detetor was plaed during the experimental setup. Samples of these output tallies are available in Appendix F. When available the S(α, β) data was used to better simulate thermal neutron behavior. Appendix G of Volume I of the MCNP5 manual [27] lists those elements for whih suh data exist. These materials inluded deuterium when ombined into heavy water, metalli beryllium, aluminum, and hydrogen in polyethylene. The exat data used is noted in the input files in Appendix B. Air (and hene air satter) is modeled in the final MCNP input files. The tally was set on a spherial surfae 100 m, and the air extended to 300 m before the simulation was ut off to aount for baksatter. 3.3 MCNP Output and Normalization to Experimental Results The MCNP fluene tallies used are already normalized per one soure neutron so these tallies must be multiplied by the soure strength used in the experiments. The soure strength used here must be divided by the number of neutrons esaping the soure per soure partile generated by MCNP, whih is a signifiant fator for the AmBe soure and it s inherit neutron multipliation. This fator was reported in the MCNP model as

47 Likewise, the total fluene and ICRP 74 ambient dose equivalent had to be multiplied by the soure. Finally, the group fluenes must be normalized per unit lethargy:. 34

48 CHAPTER 4: RESULTS This hapter ompares the results from the experimental data proessed as outlined in Chapter 2 with the omputational model outputs detailed in Chapter 3. The total fluenes, total ICRP 74 ambient dose equivalents, and neutron fluene spetra will be ompared and disussed. 4.1 Total Fluene The total fluene is expressed in terms of neutrons/m 2 /seond. It is speifi to the soures and moderators in use at the Georgia Institute of Tehnology and will be affeted over time by radioative deay. A omparison of the BUMS output and the MCNP output is in Table below. Table Total Fluene Rate Comparison Fluene Rate (n/m^2/seond) MCNP BUMS Ratio Cf-252 Bare Cf-252 Be Cf-252 Pb Cf-252 Fe Cf-252 Ta Cf-252 Poly Cf-252 D2O AmBe Bare AmBe Be AmBe Pb AmBe Fe AmBe Ta

49 The fluene rate reported by BUMS shows an overall good orrelation with that alulated from the MCNP odes. The expeted inrease in flux due to neutron multipliation in beryllium is observed. For most soure/moderator ombinations, BUMS is lose to or slightly over reports the flux ompared to the MCNP ode. The exeptions are the 252 Cf soure in lead and polyethylene. The disrepany in lead ould be due to the unusual geometry fored by the attahed stem, as pitured in Figure , and failure of the model to fully apture the geometry. The ideal representation of the stem-modified geometry in MCNP has the upper half the soure positioned where it has an almost lean line-of-sight to the detetor, passing only through a very small amount of lead at the ontat point of the two hemispheres. In reality, the alignment ould not be that perfet, and even a small displaement in the alignment auses a lot more lead to be in the line-of-sight. In addition, the equator of the two lead spheres may have tilted forward due to the shift in the enter of gravity, again plaing more lead in the line-ofsight. This results in an overreporting of flux from the MCNP ode. To test this theory, the MCNP ode was reran with the point detetor displaed various vertial distanes from the perfet enterline. A total displaement of 5m (2.9 degrees off-equator) mathed the experimental results losely. In the future, the stem must be removed from the 252 Cf for a useful field. There was also underreporting of the flux from the AmBe unmoderated soure. This experiment was ompletely redone with similar results. A systemi error is suspeted and possible auses are disussed in Chapter

50 4.2 ICRP 74 Ambient Dose Equivalent H*(10) The ICRP 74 ambient dose equivalent H*(10) is the dose equivalent in the ICRU sphere at a depth of 10 mm and is the operational quantity that area monitors are to reprodue [29]. It is measured in units of msv/seond. A omparison of the BUMS output and the MCNP output is in Table below. Table ICRP 74 Ambient Dose Equivalent H*(10) ICRP 74 Ambient dose H*(10) (msv/seond) MCNP BUMS Ratio Cf-252 Bare 9.68E E Cf-252 Be 6.56E E Cf-252 Pb 1.13E E Cf-252 Fe 5.06E E Cf-252 Ta 5.72E E Cf-252 Poly 1.11E E Cf-252 D2O 2.5E E AmBe Bare 3.63E E AmBe Be 3.1E E AmBe Pb 3.55E E AmBe Fe 2E E AmBe Ta 2.38E E The ratio of the BUMS to MCNP measured dose averages around 0.96, but flutuates between overreporting and underreporting depending on the soure/moderator ombination. (This average exludes the geometrial issues of the 252 Cf in lead setup disussed in the previous setion. The alignment hange fixed the dose equivalent results as well.) For many of the ombinations, the two results align within a few perentage points, a good orrelation for a system with limited energy resolution. The BUMS output onsistently underreports on the AmBe soure ombinations, with the iron, lead and 37

51 tantalum amounts around 10% lower. This ould be due to the maxima and minima shown in the spetrum for iron in Figure and to the sattering in the tantalum. Both of these are disussed in Chapter 4.3. BUMS losely brakets the MCNP output with the 252 Cf soure ombinations, though it overreports the dose from the polyethylene moderator by 12%. The possible explanations for these disrepanies are urrently speulative, and fous on the BSS systems lak of energy resolution in some of the areas where the ICRP 74 dose oeffiients are high. Small errors in these energy areas, whih are outside of the BSS optimal energy reporting due to the detetor response funtions shown in Figure , ould lead to large disrepanies in experimentally obtained dose readings. This ombination of relatively important dose-ontributing energy groups with those same energy groups laking resolution in the BSS is most autely seen in the 10 kev 0.1 MeV energy range. The ICRP 74 dose onversion oeffiients for H*(10) are Table A.42 in the ICRP 74 tables annex [29]. It is likely that this weakness in the BSS system and methodology ontributes to the error. In the following setion, the spetra are ompared, and figures will show how the neutron fluene spetra for some of these ombinations are in the BSS system s less aurate reporting ranges. 4.3 Neutron Fluene Spetra The total neutron fluene rate spetra are shown in this setion. They are displayed in plots of neutrons/m 2 /seond/lethargy. Energy level bounds on the figures are seleted to maximize the meaningful detail displayed. The harts are paired by 38

52 moderator when appropriate. (To visually ompare eah newly moderated spetrum to its bare soure spetrum, see the harts in Appendix G.) Also inluded is the BUMS output generated when the MCNP generated spetrum is used as the starting spetrum for the BUMS iterative proess Beryllium Sphere The beryllium sphere is pitured in Figure The resulting flux spetra are ompared in Figures and below. Figure Cf / Beryllium Sphere Spetra 39

53 Figure AmBe / Beryllium Sphere Spetra Both of these spetra show good agreement between the unfolded spetra using BUMS, with a starting spetrum generated by the MAXIET algorithm, and the MCNP alulations. Note that the smaller group struture of the MCNP alulations makes omparison on an energy-by-energy basis diffiult sine the BBS is a low resolution system. The BUMS energy groups an be arbitrarily tightened, but without more data points, there would be no real inrease in energy resolution Lead Sphere The lead sphere is pitured in Figure The resulting spetra are ompared in Figures and below. 40

54 Figure Cf / Lead Sphere Spetra 41

55 Figure AmBe / Lead Sphere Spetra The BUMS underreporting of total flux enountered for the 252 Cf soure in lead an be attributed to the rapid drop off of measured flux above 2 MeV for the BUMS spetrum. The ause of this drop-off is not ertain, but ould be related to the peuliar geometry shown in Figure This was disussed in more depth in Chapter 4.2. It ould also be a funtion of the lesser energy resolution of the BUMS system, as the MCNP ode shows a similar fluene drop-off, but has it happen more gradually with inreasing energy. 42

56 4.3.3 Iron Sphere The iron sphere is pitured in Figure The resulting spetra are ompared in Figures and below. Figure Cf / Iron Sphere Spetra 43

57 Figure AmBe / Iron Sphere Spetra The iron spetra strongly show the differene in energy resolution between the two methods. The iron moderator signifiantly shifts the energy levels of the emitted neutron fluene down towards the sub-mev range, where the BSS has relatively less energy resolution. The sharp peaks aused by maxima and minima in the iron ross setion annot be repliated by the BSS and ould have led to underreporting of dose from the AmBe soure. However, the MCNP fluene integrated over the BSS group struture would appear to be lose to the BSS group fluenies. While the BSS is not apable of apturing a spetrum with finely detailed energy resolution, it is apable of orretly estimating fluene and dose with a very simple detetor setup. 44

58 4.3.4 Tantalum Sphere The tantalum sphere is pitured in Figure The resulting spetra are ompared in Figures and below. Figure Cf / Tantalum Sphere Spetra 45

59 Figure AmBe / Tantalum Sphere Spetra The tantalum spheres shifted the spetra to lower energy levels as expeted, and reated neutron fields with smoother hanges in fluene than the jagged peaks enounter with the iron moderator. While the overall fluene and dose values traked reasonably well, these figures show that the BUMS reported peaks did not shift as muh as the MCNP peaks. This ould again be due to the limits on energy resolution, espeially below 1 MeV, for the BSS system. Sine some of this energy range is important for the dose onversion hart, it led to an underreporting of dose, espeially from the AmBe soure. 46

60 4.3.5 Bare Soure The bare soures are diagrammed in Figure and The resulting spetra are ompared in Figures and below. Figure Cf Bare Spetra 47

61 Figure AmBe Bare Spetra The bare soure measurements had the highest gamma ray bakgrounds observed and ounted in the spetra displayed in Maestro. This was manifested in the bakground ounts subtrated by the software. The 252 Cf soure results mathed up well with the MCNP ode and served to help validate the experimental method. The differenes between the spetra are explained by the lower energy resolution of the BSS. The AmBe bare soure spetrum has a signifiantly lower peak from unfolding than from alulation. Comparison to an established neutron field from the ISO 8529 publiation supports the MCNP model s results [23], also shown in Figure One possible explanation is a systemi error in measurement of the bare soure. When this disrepany was noted, a ompletely new set of experimental data was taken 48

62 for the bare AmBe soure. The setup, while ompletely reestablished after olleting other sets of data, did use the same equipment as the original test. Examining the data to see what may be unique about this situation ompared to the other data olleted shows that the overall fluene levels for the bare AmBe soure are far higher than any other soure with the exeption of a small peak in the AmBe / iron sphere ombination. It is possible that this high fluene is somehow underreported by the detetor or unfolding proess. (Dead times were within aeptable limits and similar dead times were observed in other measurements without this issue.) Also noteworthy on the BUMS spetrum is that there is a lot more low energy flux than predited by the MCNP and ISO models. Sine the moderating spheres generally do away with this low energy flux, it ould explain why the exess flux is present in the bare soure measurements but not the moderated measurements Cf in Polyethylene The polyethylene moderator ould only be used with the 252 Cf soure. The ombination is pitured in Figure The resulting spetra are ompared in Figure below. 49

63 Figure Cf / Polyethylene Spetra The downsattering from polyethylene reates interesting spetra with fluene peaks both in the MeV and thermal energy ranges, and a small but onsistent field for eight orders of magnitude in-between, although some of this may be the famed Bonner dip. Although the limited energy resolution of the BSS does overreport in the MeV range, it does apture the essene of the higher energy peak. Given the onstraints on the system measuring low energy fluenes with muh energy resolution, the BSS did a remarkable job apturing the in-between fluene and the presene of the lower energy peak. 50

64 Cf in Heavy Water The heavy water moderator ould only be used with the 252 Cf soure. The ombination is pitured in Figure The resulting spetra are ompared with ISO referene spetra in Figure [30]. Figure Cf / Heavy Water Spetra These spetra show the value of having a known starting spetrum for aurate iterative solving through BUMS. The empirial data is well-fitted to the MCNP model (whih was produed independent of the starting spetrum data in BUMS). The BUMS peak 51

65 overreports somewhat, and does so at a slightly lower energy level than the peak established by MCNP and existing literature [30]. This drop-off, while not exessively important on otherwise good fit, bears resemblane to the drop-off noted in with the AmBe soure earlier in this hapter. Both of these MCNP spetra used known starting spetra, and both spetra featured established spetra that rapidly dropped off near the 7-10 MeV energy range. Another limitation is that the BUMS system does not apture the low-energy admium utoff around 0.5 ev. The room return also may not be fully orreted for. The bakground radiation on this measurement is too high for the bare detetor measurement to apture this. 52

66 CHAPTER 5: CONCLUSION The BSS works well within its inherent energy resolution limitations. High orrelation between unfolding experimental data, MCNP models, and established standard referene spetra supported the results. Areas where disrepanies arose have either been addressed or will be addressed in future work. Due the suess of the experimental validation, the majority of the generated starting spetra for BUMS and other unfolding shemes an be published and used for further researh. Likewise, the detailed MCNP models reated an also be passed on to future users of these haraterized neutron fields, and are given in the appendies. Disrepanies between the experimental results and established values, most notably on the bare AmBe measurements, must be explained and reoniled before that data an be used. The BSS, when used with appropriate sattering and geometri orretions and a flexible unfolding algorithm, is an inexpensive, simple to operate, effetive neutron detetor. Combined with MCNP modeling, aurate fluene totals, dose, and fluene energy spetra an be olleted and analyzed in a variety of appliations. 53

67 CHAPTER 6: FUTURE WORK The first priority for future work must be to identify the soure of disrepany between the bare AmBe measurements and the established fluene total and spetrum. Explaining the drop-off above 10 MeV for unfolded data in terms of detetor or proedural limitations would lear up the only signifiant issue with the results. Using a larger number of Bonner spheres would allow for greater energy resolution, espeially if these spheres an be designed to have response peaks in energy ranges that urrent Bonner spheres do not. This is not a new idea and suh a moderator may not be found. Taking data from a larger number of soure-detetor distanes will allow better fits on the sattering parameters in the ESJ method. It would also allow testing of the orreted ount rates through seletively disregarding individual distane sets to see how sensitive the orreted data is to eah point measured at. The usefulness of some of the 252 Cf geometries is onstrained by the stem, espeially when using the lead sphere. The stem must be removed in the future for more useful results. The most important future work will be researh that uses these published spetra and MCNP input odes as the foundation for work with these haraterized neutron fields. 54

68 APPENDIX A: STARTING SPECTRA FOR ITERATIVE UNFOLDING 55

69 Appendix Notes: 1. Listings are in a raw format that an be diretly opy and pasted into a text file that an be parsed by BUMS. 2. The first olumn is the top of the energy bin in MeV. 3. The seond olumn is the fluene in neutrons/m 2 /seond/lethargy. 4. Only spetra not already present in BUMS are listed. A Cf in Be Starting Spetrum Cf in 10.16m r Be sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-01 56

70 A Cf in Pb Starting Spetrum Cf in 19 m r Pb sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-01 57

71 58 A Cf in Fe Starting Spetrum Cf in 30"d Fe sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-03

72 A Cf in Ta Starting Spetrum Cf in m r Ta sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-02 59

73 60 A Cf in Polyethylene Starting Spetrum Cf in 12" d Poly sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-02

74 61 A.6 AmBe in Be Starting Spetrum AmBe in m r Be sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-03

75 62 A.7 AmBe in Pb Starting Spetrum AmBe in 19m r Pb sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-03

76 63 A.8 AmBe in Fe Starting Spetrum AmBe in 30" d Fe sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-05

77 64 A.9 AmBe in Ta Starting Spetrum AmBe in m r Ta sphere 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-03

78 APPENDIX B: MCNP INPUT FILES 65

79 Appendix notes: 1. MCNP files are displayed in a raw format that an be opy/pasted into a text editor and saved as an MCNP input file. 2. Some previous modeling work for the soures was done by N. E. Hertel. Muh of the 252 Cf bare soure model is based on his previous unpublished work. 3. The remainder of the model files is the produt of the author and may be reused as long as redit is given. B Cf Bare MCNP Input Cf Bare by Pete Exline Cell Cards ells for bare soure with no PNL rabbit ***PRIMARY ENCAPSULATION*** CF oxide soure volume (no material assumed for the moment** imp:n=1 imp:p=1 Lower porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Lower void imp:n=1 imp:p=1 Middle void imp:n=1 imp:p=1 upper porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Upper void imp:n=1 imp:p=1 Primary apsule ontainer (90% Pt and 10% Rh) #( : ) imp:n=1 imp:p=1 Gap between the primnary and seondary apsules 8 0 #( ) ( ):( ) imp:n=1 imp:p=1 **SECONDARY CAPSULE OF ZIRCALLOY-2*** #( ) (-4 8-3):-8 9-5: imp:n=1 imp:p=1 The threads of the seondary apsule imp:n=1 imp:p=1 Air outside the soure -- used as a tally surfae e-3 ( ):( ):( ):& (-322 2):(-322-9) imp:n=1 imp:p=1 Air beyond the tally surfae to edge of universe e imp:n=1 imp:p=1 66

80 imp:n=0 imp:p=0 $terminate partiles beyond universe XXXXXXX** air to ombine for Be Sphere ** e-3 ( ):( ):( ):(-301 2):(-301-9) & imp:n=1 imp:p=1 Surfae Cards Cylinder and planes to define the theaded portion of the seondary apsule 1 CZ PZ PZ Cylinders to define the seondary enapsulation 4 CZ CZ CZ planes and one to define the seonday enapsulation 7 PZ PZ PZ KZ Cylinders to define the primary enapsulation 11 CZ CZ CZ Planes to define the primary enapsulation 14 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ SO 100 $100m Sphere around soure 24 SO 500 $edge of universe The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ

81 341 PZ PZ ** Material Cards Materials: M1 is the porous filter, M2 is the 90% Pt, 10% Rh and M4 is the Ziralloy-2 M M M & & ** m $air ** the soure is input in ell one region using a Maxwellian with temperature of 1.42 MeV old syntax -- SRC4 3J SDEF ERG=D1 CEL=1 PAR =1 POS=0 0 0 AXS=0 0 1 EXT=D3 RAD=D2 SI SI SP SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

82 e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E-01 69

83 1.50E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 70

84 B Cf in Beryllium MCNP Input Cf in 20.32m d Be sphere by Pete Exline Cell Cards ells for bare soure with no PNL rabbit ***PRIMARY ENCAPSULATION*** CF oxide soure volume (no material assumed for the moment** imp:n=1 imp:p=1 Lower porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Lower void imp:n=1 imp:p=1 Middle void imp:n=1 imp:p=1 upper porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Upper void imp:n=1 imp:p=1 Primary apsule ontainer (90% Pt and 10% Rh) #( : ) imp:n=1 imp:p=1 Gap between the primnary and seondary apsules 8 0 #( ) ( ):( ) imp:n=1 imp:p=1 **SECONDARY CAPSULE OF ZIRCALLOY-2*** #( ) (-4 8-3):-8 9-5: imp:n=1 imp:p=1 The threads of the seondary apsule imp:n=1 imp:p=1 ** Be Sphere ** e-3 ( #(& ( ):& (( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ))))& imp:n=1 imp:p=1 $air from Be surfae to tally sphere e imp:n=1 imp:p=1 $air from sphere to edge of universe Be sphere (with last two terms removing plug) (308:-312) (309:-311) imp:n=1 imp:p= imp:n=0 imp:p=0 $Void spae outside universe plug removed e ( ):( ) & 71

85 imp:n=1 imp:p=1 ** air to ombine for Be Sphere ** e-3 ( ):( ):( ):(-301 2):(-301-9) & imp:n=1 imp:p=1 * Al table top* imp:n=1 imp:p=1 $Al table top ( ):( ) & imp:n=1 imp:p=1 $bl leg ( ):( ) & imp:n=1 imp:p=1 $br leg ( ):( ) & imp:n=1 imp:p=1 $tl leg ( ):( ) & imp:n=1 imp:p=1 $tr leg ( ):( ) & imp:n=1 imp:p=1 $bl thik leg ( ):( ) & imp:n=1 imp:p=1 $br thik leg ( ):( ) & imp:n=1 imp:p=1 $tl thik leg ( ):( ) & imp:n=1 imp:p=1 $tr thik leg imp:n=1 imp:p=1 $Al stabilizer ring ** Surfae Cards Cylinder and planes to define the theaded portion of the seondary apsule 1 CZ PZ PZ Cylinders to define the seondary enapsulation 4 CZ CZ CZ planes and one to define the seonday enapsulation 7 PZ PZ PZ KZ Cylinders to define the primary enapsulation 11 CZ CZ CZ Planes to define the primary enapsulation 14 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ **Be Sphere ** 301 SO $Outer surfae of soure sphere 306 SO 500 $Edge of the Universe 307 SO $radius of Be spherial shell 72

86 308 CZ $small radius of plug 309 CZ $larger radius of plug lip 310 PZ $bottom of plug 311 PZ 8.89 $bottom of plug lip 312 PZ $used to define upper half for plug geometries 322 SO 100 $100m Sphere around soure ** *Al table top* 501 pz $top of Al table top 502 pz $bot of Al table top 503 px $left of Al table top 504 px $right of Al table top 505 py $front of Al table top 506 py $bak of Al table top 513 px $left of Al table leg 514 px $right of Al table leg 515 py $front of Al table leg 516 py $bak of Al table leg 523 px $utoff of Al table top 524 px $utoff of Al table top 525 py $utoff of Al table top 526 py $utoff of Al table top 531 pz $bot of thin legs/top of thik legs 543 px $left of Al table thik leg 544 px $right of Al table thik leg 545 py $front of Al table thik leg 546 py $bak of Al table thik leg 551 z 6.25 $inner radius of Al stabilizer 552 z 8.75 $outer radius of Al stabilizer 553 pz $top of Al stablizer ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards Materials: M1 is the porous filter, M2 is the 90% Pt, 10% Rh and M4 is the Ziralloy-2 M M M & & ** Be Sphere ** m ** m $air 73

87 ** m $Al the soure is input in ell one region using a Maxwellian with temperature of 1.42 MeV old syntax -- SRC4 3J SDEF ERG=D1 CEL=1 PAR =1 POS=0 0 0 AXS=0 0 1 EXT=D3 RAD=D2 SI SI SP SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E-02 74

88 1.99E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de

89 df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 76

90 B Cf in Lead MCNP Input Cf in m r Pb sphere by Pete Exline Cell Cards ells for bare soure with no PNL rabbit ***PRIMARY ENCAPSULATION*** CF oxide soure volume (no material assumed for the moment** imp:n=1 imp:p=1 Lower porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Lower void imp:n=1 imp:p=1 Middle void imp:n=1 imp:p=1 upper porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Upper void imp:n=1 imp:p=1 Primary apsule ontainer (90% Pt and 10% Rh) #( : ) imp:n=1 imp:p=1 Gap between the primnary and seondary apsules 8 0 #( ) ( ):( ) imp:n=1 imp:p=1 **SECONDARY CAPSULE OF ZIRCALLOY-2*** #( ) (-4 8-3):-8 9-5: imp:n=1 imp:p=1 The threads of the seondary apsule imp:n=1 imp:p=1 ** Pb Sphere ** e-3 #( ) #( ) & ( #(& ( ):& (( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ))))& imp:n=1 imp:p=1 $air from Pb surfae to tally sph e imp:n=1 imp:p=1 $air from sphere to edge of univ imp:n=1 imp:p=1 $Pb sphere bottom imp:n=0 imp:p=0 $Void spae outside universe imp:n=1 imp:p=1 $Pb sphere top ** 77

91 ** air to ombine for Pb Sphere ** e-3 ( ):( ):( ):(-302 2):(-302-9) & imp:n=1 imp:p=1 * Al table top* imp:n=1 imp:p=1 $Al table top ( ):( ) & imp:n=1 imp:p=1 $bl leg ( ):( ) & imp:n=1 imp:p=1 $br leg ( ):( ) & imp:n=1 imp:p=1 $tl leg ( ):( ) & imp:n=1 imp:p=1 $tr leg ( ):( ) & imp:n=1 imp:p=1 $bl thik leg ( ):( ) & imp:n=1 imp:p=1 $br thik leg ( ):( ) & imp:n=1 imp:p=1 $tl thik leg ( ):( ) & imp:n=1 imp:p=1 $tr thik leg imp:n=1 imp:p=1 $Al stabilizer ring ** Surfae Cards Cylinder and planes to define the theaded portion of the seondary apsule 1 CX PX PX Cylinders to define the seondary enapsulation 4 CX CX CX planes and one to define the seonday enapsulation 7 PX PX PX KX Cylinders to define the primary enapsulation 11 CX CX CX Planes to define the primary enapsulation 14 PX PX PX PX PX PX PX PX PX PX PX **Pb Sphere ** 301 SO $Outer surfae of Pb Sphere (bot hem) 302 SO 3.05 $inner void for soure (bot hem) 303 PZ 0 $top of bottom hemisphere 304 S $Pb top hemisphere sphere 78

92 305 S $inner void for soure (top hem) 306 SO 500 $Edge of the Universe 307 P SO 100 $100m tally sphere around soure ** *Al table top* 501 pz $top of Al table top 502 pz $bot of Al table top 503 px $left of Al table top 504 px $right of Al table top 505 py $front of Al table top 506 py $bak of Al table top 513 px $left of Al table leg 514 px $right of Al table leg 515 py $front of Al table leg 516 py $bak of Al table leg 523 px $utoff of Al table top 524 px $utoff of Al table top 525 py $utoff of Al table top 526 py $utoff of Al table top 531 pz $bot of thin legs/top of thik legs 543 px $left of Al table thik leg 544 px $right of Al table thik leg 545 py $front of Al table thik leg 546 py $bak of Al table thik leg 551 z 6.25 $inner radius of Al stabilizer 552 z 8.75 $outer radius of Al stabilizer 553 pz $top of Al stablizer ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards Materials: M1 is the porous filter, M2 is the 90% Pt, 10% Rh and M4 is the Ziralloy-2 M M M & & ** Pb Sphere ** m ** m $air ** m $Al 79

93 the soure is input in ell one region using a Maxwellian with temperature of 1.42 MeV old syntax -- SRC4 3J SDEF ERG=D1 CEL=1 PAR =1 POS=0 0 0 AXS=0 0 1 EXT=D3 RAD=D2 SI SI SP SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-01 80

94 3.16E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de

95 df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 82

96 B Cf in Iron MCNP Input Cf in 30" Fe sphere by Pete Exline Cell Cards ells for bare soure with no PNL rabbit ***PRIMARY ENCAPSULATION*** CF oxide soure volume (no material assumed for the moment** imp:n=1 imp:p=1 Lower porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Lower void imp:n=1 imp:p=1 Middle void imp:n=1 imp:p=1 upper porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Upper void imp:n=1 imp:p=1 Primary apsule ontainer (90% Pt and 10% Rh) #( : ) imp:n=1 imp:p=1 Gap between the primnary and seondary apsules 8 0 #( ) ( ):( ) imp:n=1 imp:p=1 **SECONDARY CAPSULE OF ZIRCALLOY-2*** #( ) (-4-8 3):8-9 -5: imp:n=1 imp:p=1 The threads of the seondary apsule imp:n=1 imp:p=1 ** Fe Sphere ** e #( ) & #( ) & #( ) & #( ) & #( ) & #(( ):( & )) & #(( ):( & )) & #( ) & #( ) & #(-533:( )) & #(-534:( )) & #( ) & #( ) & #( ) imp:n=1 imp:p=1 $air from Fe surfae to tally sph e imp:n=1 imp:p=1 $air imp:n=1 imp:p=1 $void from sphere to edge of univ 83

97 (303:309) (305:311) (310:304) (308:-311) & imp:n=1 imp:p=1 $Fe sphere imp:n=0 imp:p=0 $Void spae outside universe imp:n=1 imp:p=1 $plugged right tube e #( ) imp:n=1 imp:p=1 $left tube ( ):( ) & imp:n=1 imp:p=1 $plugged bottom tube imp:n=1 imp:p=1 $plugged top tube imp:n=1 imp:p=1 $smaller plug for left tube ** ** Fe Stand ** imp:n=1 imp:p=1 $base plate imp:n=1 imp:p=1 $l upp base imp:n=1 imp:p=1 $r upp base imp:n=1 imp:p=1 $l support imp:n=1 imp:p=1 $r support ( ):( & ) imp:n=1 imp:p=1 $left support ap ( ):( & ) imp:n=1 imp:p=1 $right support ap imp:n=1 imp:p=1 $left ap ring imp:n=1 imp:p=1 $right ap ring :( ) imp:n=1 imp:p=1 $left eyelet :( ) imp:n=1 imp:p=1 $right eyelet imp:n=1 imp:p=1 $left flange imp:n=1 imp:p=1 $right flange ** ** Air to ombine for Fe Sphere ** e-3 ( ):( ):( ):(-302-2):(-302 9)& imp:n=1 imp:p=1 Surfae Cards Cylinder and planes to define the theaded portion of the seondary apsule 1 CX PX PX Cylinders to define the seondary enapsulation 4 CX CX CX planes and one to define the seonday enapsulation 7 PX PX PX KX Cylinders to define the primary enapsulation 11 CX CX CX Planes to define the primary enapsulation 14 PX PX PX PX PX PX PX PX

98 22 PX PX PX **Fe Sphere ** 301 SO 38.1 $Outer surfae of Fe Sphere 306 SO 500 $Edge of the Universe 302 SO 7.62 $inner void for soure 303 CX $onstant radius tube from left 304 PY $plane to define radius hange point in bottom entry 305 CY 5.08 $tube from bottom (smaller radius) 310 CY 6.35 $tube from bottom (larger radius) 307 C/Y $tube on right side 308 CY 1.27 $used to define upper half for plug geometries 309 PX 0 $used to stop tubes on left/right of origin 311 PY 0 $used to stop tubes on top/bottom of origin 312 PX $top of shape used to move left plug out due to Cf attahment 313 PX $bottom of left plug ylinder 314 CX 4.25 $smaller left plug 322 SO 100 $100m Sphere around soure ** **Fe Stand** 501 PZ $bottom of base plate 502 PZ $top of base plate and bot of upper base 503 PY $top edge of base plate 504 PY $bottom edge of base plate 505 PX $left edge of base plate and upper base 506 PX $right edge of base plate and upper base 507 PZ $top of upper base 508 PY $top edge of upper base 509 PY $bot edge of upper base 510 PX $right edge of l upper base 511 PX $left edge of r upper base 512 P P PX $left support left edge 515 PX $right support left edge 516 PX $left support right edge 517 PX $right support right edge 518 PZ 0 $supports top edge 519 PZ $ap srew flange top 520 PY $ap left vert 521 PY $ap right vert 522 P $ap left diagonal 523 P $ap right diagonal 524 PZ $ap top 525 PY $ap left edge 526 PY 12.7 $ap right edge 527 CX $inner radius ap ring {set to math port radius} 528 CX $outer radius ap rin 529 PX $outer edge of left ap ring 530 PX $outer edge of right ap ring 531 PX $inner edge of left ap ring {adjusted to fit imperfet sphere} 532 PX $inner edge of right ap ring {adjusted to fit imperfet sphere} 533 TX $left eyelet 534 TX $right eyelet 535 C/Z $left eyelet onnetor walls 536 C/Z $right eyelet onnetor walls 537 PZ 12.7 $eyelet onnetor top utoff 538 PY $bottom edge of flagnes 539 PY.635 $top edge of flanges 540 PZ $top of flanges (tapered ompletely off) 541 P P ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ

99 325 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards Materials: M1 is the porous filter, M2 is the 90% Pt, 10% Rh and M4 is the Ziralloy-2 M M M & & ** Fe Sphere ** m & m $air ** the soure is input in ell one region using a Maxwellian with temperature of 1.42 MeV old syntax -- SRC4 3J SDEF ERG=D1 CEL=1 PAR =1 POS=0 0 0 AXS=0 0 1 EXT=D3 RAD=D2 SI SI SP SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs 86

100 F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E-03 87

101 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 88

102 B Cf in Tantalum MCNP Input Cf in Ta by Pete Exline Cell Cards ells for bare soure with no PNL rabbit ***PRIMARY ENCAPSULATION*** CF oxide soure volume (no material assumed for the moment** imp:n=1 imp:p=1 Lower porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Lower void imp:n=1 imp:p=1 Middle void imp:n=1 imp:p=1 upper porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Upper void imp:n=1 imp:p=1 Primary apsule ontainer (90% Pt and 10% Rh) #( : ) imp:n=1 imp:p=1 Gap between the primnary and seondary apsules 8 0 #( ) ( ):( ) imp:n=1 imp:p=1 **SECONDARY CAPSULE OF ZIRCALLOY-2*** #( ) (-4 8-3):-8 9-5: imp:n=1 imp:p=1 The threads of the seondary apsule imp:n=1 imp:p=1 ** Ta Sphere ** e-3 ( #(( ):( ):& ( ):& ( ):& ( ):( ):& (( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ))& ))& :(-308 #( ) & #( )):-309 & imp:n=1 imp:p=1 $air from Ta surfae to tally sphere e imp:n=1 imp:p=1 $air from sphere to edge of universe 89

103 imp:n=1 imp:p=1 $Ta Sphere imp:n=0 imp:p=0 $Void spae outside universe imp:n=1 imp:p=1 $aluminum ring 1 (in groove) ( ):( ):& ( ):& ( ) imp:n=1 imp:p=1 $aluminum ring imp:n=1 imp:p=1 $aluminum ring 3 * Al table top* imp:n=1 imp:p=1 $Al table top ( ):( ) & imp:n=1 imp:p=1 $bl leg ( ):( ) & imp:n=1 imp:p=1 $br leg ( ):( ) & imp:n=1 imp:p=1 $tl leg ( ):( ) & imp:n=1 imp:p=1 $tr leg ( ):( ) & imp:n=1 imp:p=1 $bl thik leg ( ):( ) & imp:n=1 imp:p=1 $br thik leg ( ):( ) & imp:n=1 imp:p=1 $tl thik leg ( ):( ) & imp:n=1 imp:p=1 $tr thik leg imp:n=1 imp:p=1 $Al stabilizer ring ** ** air to ombine for Ta Sphere ** e-3 ( ):( ):( ):(-301 2):(-301-9) & imp:n=1 imp:p=1 Surfae Cards Cylinder and planes to define the theaded portion of the seondary apsule 1 CY PY PY Cylinders to define the seondary enapsulation 4 CY CY CY planes and one to define the seonday enapsulation 7 PY PY PY KY Cylinders to define the primary enapsulation 11 CY CY CY Planes to define the primary enapsulation 14 PY PY PY PY PY PY PY PY PY

104 23 PY PY **Ta Sphere ** 301 SO $Outer surfae of soure sphere 306 SO 500 $Edge of the Universe 307 SO 12 $radius of Ta spherial shell 308 tz $top groove 309 tz $bottom groove 322 SO 100 $100m Sphere around soure 310 z 11.7 $Al ring inner radius in groove 313 z 14.1 $Al ring outer radius (all) 311 pz.9 $top of Al ring in groove 312 pz.6 $bottom of Al Ring in groove / top of ring z 12.1 $Al ring inner radius (ring 2/3) 315 pz.3 $bottom of ring 2 / top of ring pz 0 $bottom of ring py 1.9 $top of lift arms 318 py -1.9 $bot of lift arms 319 C/Z $l round edge of lift arm 320 C/Z $r round edge of lift arm 360 px 32.7 $utoff of straight part of lift arm 361 px $utoff of straight part of lift arm *Al table top* 501 pz $top of Al table top 502 pz $bot of Al table top 503 px $left of Al table top 504 px $right of Al table top 505 py $front of Al table top 506 py $bak of Al table top 513 px $left of Al table leg 514 px $right of Al table leg 515 py $front of Al table leg 516 py $bak of Al table leg 523 px $utoff of Al table top 524 px $utoff of Al table top 525 py $utoff of Al table top 526 py $utoff of Al table top 531 pz $bot of thin legs/top of thik legs 543 px $left of Al table thik leg 544 px $right of Al table thik leg 545 py $front of Al table thik leg 546 py $bak of Al table thik leg 551 z 6.25 $inner radius of Al stabilizer 552 z 8.75 $outer radius of Al stabilizer 553 pz $top of Al stablizer ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** 91

105 Material Cards Materials: M1 is the porous filter, M2 is the 90% Pt, 10% Rh and M4 is the Ziralloy-2 M M M & & ** Ta Sphere ** m $Ta m $Al ** m $air ** the soure is input in ell one region using a Maxwellian with temperature of 1.42 MeV old syntax -- SRC4 3J SDEF ERG=D1 CEL=1 PAR =1 POS=0 0 0 AXS=0 0 1 EXT=D3 RAD=D2 SI SI SP SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

106 e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E-01 93

107 1.50E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 94

108 B Cf in Polyethylene MCNP Input Cf in 12" poly by Pete Exline Cell Cards ells for bare soure with no PNL rabbit ***PRIMARY ENCAPSULATION*** CF oxide soure volume (no material assumed for the moment** imp:n=1 imp:p=1 Lower porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Lower void imp:n=1 imp:p=1 Middle void imp:n=1 imp:p=1 upper porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Upper void imp:n=1 imp:p=1 Primary apsule ontainer (90% Pt and 10% Rh) #( : ) imp:n=1 imp:p=1 Gap between the primnary and seondary apsules 8 0 #( ) ( ):( ) imp:n=1 imp:p=1 **SECONDARY CAPSULE OF ZIRCALLOY-2*** #( ) (-4 8-3):-8 9-5: imp:n=1 imp:p=1 The threads of the seondary apsule imp:n=1 imp:p=1 ** Poly Sphere ** e imp:n=1 imp:p=1 $air from Poly surfae to tally sph e imp:n=1 imp:p=1 $air from sphere to edge of univ (302:-303) imp:n=1 imp:p=1 $Poly sphere imp:n=0 imp:p=0 $Void spae outside universe ** ** Air to ombine for Poly Sphere ** e-3 ( ):( ):( & ):( ):( ) imp:n=1 imp:p=1 Surfae Cards Cylinder and planes to define the theaded portion of the seondary apsule 1 CZ PZ PZ Cylinders to define the seondary enapsulation 95

109 4 CZ CZ CZ planes and one to define the seonday enapsulation 7 PZ PZ PZ KZ Cylinders to define the primary enapsulation 11 CZ CZ CZ Planes to define the primary enapsulation 14 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ **Poly Sphere ** 301 SO 15 $Outer surfae of Poly Sphere 306 SO 500 $Edge of the Universe 302 CZ.75 $hole for soure 303 PZ -2 $bottom of hole 322 SO 100 $100m Sphere around soure The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards Materials: M1 is the porous filter, M2 is the 90% Pt, 10% Rh and M4 is the Ziralloy-2 M M

110 M & & ** Poly Sphere ** m $from PNNL pdf mt301 poly.10t $H in poly at 293k ** m $air ** the soure is input in ell one region using a Maxwellian with temperature of 1.42 MeV old syntax -- SRC4 3J SDEF ERG=D1 CEL=1 PAR =1 POS=0 0 0 AXS=0 0 1 EXT=D3 RAD=D2 SI SI SP SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+00 97

111 1.25E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF

112 ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 99

113 B Cf in D 2 O MCNP Input Cf in D2O Sphere w/ Cd Cover by Pete Exline Cell Cards ells for bare soure with no PNL rabbit ***PRIMARY ENCAPSULATION*** CF oxide soure volume (no material assumed for the moment** imp:n=1 imp:p=1 Lower porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Lower void imp:n=1 imp:p=1 Middle void imp:n=1 imp:p=1 upper porous platinum filter (1/2 full density assumed) imp:n=1 imp:p=1 Upper void imp:n=1 imp:p=1 Primary apsule ontainer (90% Pt and 10% Rh) #( : ) imp:n=1 imp:p=1 Gap between the primnary and seondary apsules 8 0 #( ) ( ):( ) imp:n=1 imp:p=1 **SECONDARY CAPSULE OF ZIRCALLOY-2*** #( ) (-4 8-3):-8 9-5: imp:n=1 imp:p=1 The threads of the seondary apsule imp:n=1 imp:p=1 ** D2O Sphere ** e :( ) imp:n=1 imp:p=1 $air from D2O & surfae to tally sph e imp:n=1 imp:p=1 $air from tally to edge of univ #( ) imp:n=1 imp:p=1 $D2O sphere imp:n=0 imp:p=0 $Void spae outside universe #( ) imp:n=1 imp:p=1 $steel wall ( ):( ) imp:n=1 imp:p=1 $steel hole wall #( ) imp:n=1 imp:p=1 $Cd over ** ** Air to ombine for D2O Sphere ** e-3 ( ):( ):( & ):( ):( ) imp:n=1 imp:p=1 Surfae Cards Cylinder and planes to define the theaded portion of the seondary apsule 1 CZ

114 2 PZ PZ Cylinders to define the seondary enapsulation 4 CZ CZ CZ planes and one to define the seonday enapsulation 7 PZ PZ PZ KZ Cylinders to define the primary enapsulation 11 CZ CZ CZ Planes to define the primary enapsulation 14 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ **D2O Sphere ** 301 SO 15 $Outer surfae of D2O Sphere 304 SO $Outer surfae of Steel sphere 305 SO $Outer surfae of the Cd Sphere 306 SO 500 $Edge of the Universe 302 CZ.5 $hole for soure 307 CZ.54 $Steel wall of hole for soure 303 PZ -2 $bottom of hole 308 PZ $bottom of Steel over of hole 322 SO 100 $100m Sphere around soure ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** 101

115 Material Cards Materials: M1 is the porous filter, M2 is the 90% Pt, 10% Rh and M4 is the Ziralloy-2 M M M & & ** D2O Sphere ** m $heavy water mt301 hwtr.10t $heavy water H-2 treatment at 293K m & $stainless steel m & $Cd m $air ** the soure is input in ell one region using a Maxwellian with temperature of 1.42 MeV old syntax -- SRC4 3J SDEF ERG=D1 CEL=1 PAR =1 POS=0 0 0 AXS=0 0 1 EXT=D3 RAD=D2 SI SI SP SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

116 3.16E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E

117 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 104

118 B.8 AmBe Bare MCNP Input AmBe bare by Pete Exline Cell Cards (-2-3 4):(-2-5) imp:n=1 imp:p=1 $AmBe Soure Region #(( ):& ( ):( ):& ( ):( )) imp:n=1 imp:p=1 $void spring area (-1 2):(3-1) imp:n=1 imp:p=1 $SS304 Shell leaf spring - enter:left:far left:right:far right ( ):( ):& ( ):( ):& ( ) imp:n=1 imp:p=1 ** air to ombine for Bare ** e imp:n=1 imp:p=1 $air from AmBe to tally sphere e imp:n=1 imp:p=1 $air from tally sphere to edge of uni imp:n=0 imp:p=0 $va past edge of universe Surfae Cards 1 SO $Outer surfae of soure sphere 2 SO $Inner Radius of SS304 Layer 3 PZ $Upper Bound on AmBe Material 4 PZ $Upper Bound on Void Spae 5 PZ $Lower Bound on Void Spae 63 C/Y $leaf spring middle irle outer 64 C/Y $leaf spring left irle outer 65 C/Y $leaf spring right irle outer 66 C/Y $leaf spring middle irle inner 67 C/Y $leaf spring left irle inner 68 C/Y $leaf spring right irle inner 71 PZ $end spring l/r 72 PY $edge of width of spring 73 PY 1.27 $edge of width of spring 74 PX $used to treat inner half of small urve different for utoffs 75 PX $used to treat inner half of small urve different for utoffs 76 PZ 0.01 $used to fix what 75 does in allowing top of irles 77 p p SO 500 $Edge of the Universe 322 SO 100 $100m Sphere around soure ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards 105

119 m $AmBe SS304 m & m $air ** Soure sdef par=1 erg=d1 RAD=D2 CEL=1 SI1 4.14e & & & & & & & sp & & & & & & & & & sb R SI SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E

120 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF

121 ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 108

122 B.9 AmBe in Beryllium MCNP Input AmBe in m r Be sphere by Pete Exline Cell Cards (-2-3 4):(-2-5) imp:n=1 imp:p=1 $AmBe Soure Region #(( ):& ( ):( ):& ( ):( )) imp:n=1 imp:p=1 $void spring area (-1 2):(3-1) imp:n=1 imp:p=1 $SS304 Shell leaf spring - enter:left:far left:right:far right ( ):( ):& ( ):( ):& ( ) imp:n=1 imp:p=1 ** Be Sphere ** e-3 ( #(& ( ):& (( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ))))& imp:n=1 imp:p=1 $air from Be surfae to tally sphere e imp:n=1 imp:p=1 $air from sphere to edge of universe Be sphere (with last two terms removing plug) (308:-312) (309:-311) imp:n=1 imp:p= imp:n=0 imp:p=0 $Void spae outside universe plug in plae ( ):( ) & imp:n=1 imp:p=1 ** air to ombine for Be Sphere ** e-3 ( ):( ):( ):(-301-2):(-301 9) & imp:n=1 imp:p=1 * Al table top* imp:n=1 imp:p=1 $Al table top ( ):( ) & imp:n=1 imp:p=1 $bl leg ( ):( ) & imp:n=1 imp:p=1 $br leg ( ):( ) & imp:n=1 imp:p=1 $tl leg ( ):( ) & imp:n=1 imp:p=1 $tr leg ( ):( ) & imp:n=1 imp:p=1 $bl thik leg ( ):( ) & imp:n=1 imp:p=1 $br thik leg ( ):( ) & imp:n=1 imp:p=1 $tl thik leg ( ):( ) & imp:n=1 imp:p=1 $tr thik leg imp:n=1 imp:p=1 $Al stabilizer ring ** Surfae Cards 1 SO $Outer surfae of soure sphere 2 SO $Inner Radius of SS304 Layer 3 PZ $Upper Bound on AmBe Material 4 PZ $Upper Bound on Void Spae 5 PZ $Lower Bound on Void Spae 63 C/Y $leaf spring middle irle outer 64 C/Y $leaf spring left irle outer 65 C/Y $leaf spring right irle outer 66 C/Y $leaf spring middle irle inner 109

123 67 C/Y $leaf spring left irle inner 68 C/Y $leaf spring right irle inner 71 PZ $end spring l/r 72 PY $edge of width of spring 73 PY 1.27 $edge of width of spring 74 PX $used to treat inner half of small urve different for utoffs 75 PX $used to treat inner half of small urve different for utoffs 76 PZ 0.01 $used to fix what 75 does in allowing top of irles 77 p p **Be Sphere ** 301 SO $Outer surfae of soure sphere 306 SO 500 $Edge of the Universe 307 SO $radius of Be spherial shell 308 CZ $small radius of plug 309 CZ $larger radius of plug lip 310 PZ $bottom of plug 311 PZ 8.89 $bottom of plug lip 312 PZ $used to define upper half for plug geometries 322 SO 100 $100m Sphere around soure ** *Al table top* 501 pz $top of Al table top 502 pz $bot of Al table top 503 px $left of Al table top 504 px $right of Al table top 505 py $front of Al table top 506 py $bak of Al table top 513 px $left of Al table leg 514 px $right of Al table leg 515 py $front of Al table leg 516 py $bak of Al table leg 523 px $utoff of Al table top 524 px $utoff of Al table top 525 py $utoff of Al table top 526 py $utoff of Al table top 531 pz $bot of thin legs/top of thik legs 543 px $left of Al table thik leg 544 px $right of Al table thik leg 545 py $front of Al table thik leg 546 py $bak of Al table thik leg 551 z 6.25 $inner radius of Al stabilizer 552 z 8.75 $outer radius of Al stabilizer 553 pz $top of Al stablizer ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** 110

124 Material Cards m $AmBe SS304 m & ** Be Sphere ** m ** m $air ** m $Al Soure sdef par=1 erg=d1 RAD=D2 CEL=1 SI1 4.14e & & & & & & & sp & & & & & & & & & sb R SI SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m 111

125 F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

126 2.01E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 113

127 B.10 AmBe in Lead MCNP Input AmBe in m r Pb sphere by Pete Exline Cell Cards (-2-3 4):(-2-5) imp:n=1 imp:p=1 $AmBe Soure Region #(( ):& ( ):( ):& ( ):( )) imp:n=1 imp:p=1 $void spring area (-1 2):(3-1) imp:n=1 imp:p=1 $SS304 Shell leaf spring - enter:left:far left:right:far right ( ):( ):& ( ):( ):& ( ) imp:n=1 imp:p=1 ** Pb Sphere ** e-3 ( #(& ( ):& (( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ))))& imp:n=1 imp:p=1 $air from Pb surfae to tally sph e imp:n=1 imp:p=1 $air from tally to edge of univ imp:n=1 imp:p=1 $Pb sphere imp:n=0 imp:p=0 $Void spae outside universe imp:n=1 imp:p=1 $Pb sphere top ** * Al table top* imp:n=1 imp:p=1 $Al table top ( ):( ) & imp:n=1 imp:p=1 $bl leg ( ):( ) & imp:n=1 imp:p=1 $br leg ( ):( ) & imp:n=1 imp:p=1 $tl leg ( ):( ) & imp:n=1 imp:p=1 $tr leg ( ):( ) & imp:n=1 imp:p=1 $bl thik leg ( ):( ) & imp:n=1 imp:p=1 $br thik leg ( ):( ) & imp:n=1 imp:p=1 $tl thik leg ( ):( ) & imp:n=1 imp:p=1 $tr thik leg imp:n=1 imp:p=1 $Al stabilizer ring ** Surfae Cards 1 SO $Outer surfae of soure sphere 2 SO $Inner Radius of SS304 Layer 3 PZ $Upper Bound on AmBe Material 4 PZ $Upper Bound on Void Spae 5 PZ $Lower Bound on Void Spae 63 C/Y $leaf spring middle irle outer 64 C/Y $leaf spring left irle outer 65 C/Y $leaf spring right irle outer 66 C/Y $leaf spring middle irle inner 67 C/Y $leaf spring left irle inner 68 C/Y $leaf spring right irle inner 71 PZ $end spring l/r 72 PY $edge of width of spring 73 PY 1.27 $edge of width of spring 114

128 74 PX $used to treat inner half of small urve different for utoffs 75 PX $used to treat inner half of small urve different for utoffs 76 PZ 0.01 $used to fix what 75 does in allowing top of irles 77 p p **Pb Sphere ** 301 SO $Outer surfae of Pb Sphere (bot hem) 302 SO $inner void for soure (bot hem) 303 PZ 0 $top of bottom hemisphere 304 S $Pb top hemisphere sphere 305 S $inner void for soure (top hem) 306 SO 500 $Edge of the Universe 307 P SO 100 $100m tally sphere around soure ** *Al table top* 501 pz $top of Al table top 502 pz $bot of Al table top 503 px $left of Al table top 504 px $right of Al table top 505 py $front of Al table top 506 py $bak of Al table top 513 px $left of Al table leg 514 px $right of Al table leg 515 py $front of Al table leg 516 py $bak of Al table leg 523 px $utoff of Al table top 524 px $utoff of Al table top 525 py $utoff of Al table top 526 py $utoff of Al table top 531 pz $bot of thin legs/top of thik legs 543 px $left of Al table thik leg 544 px $right of Al table thik leg 545 py $front of Al table thik leg 546 py $bak of Al table thik leg 551 z 6.25 $inner radius of Al stabilizer 552 z 8.75 $outer radius of Al stabilizer 553 pz $top of Al stablizer ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards m $AmBe SS304 m & 115

129 ** Pb Sphere ** m ** m $air ** m $Al Soure sdef par=1 erg=d1 RAD=D2 CEL=1 SI1 4.14e & & & & & & & sp & & & & & & & & & sb R SI SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E

130 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF

131 ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 118

132 B.11 AmBe in Iron MCNP Input AmBe in 30" d Fe sphere by Pete Exline Cell Cards (-2-3 4):(-2-5) imp:n=1 imp:p=1 $AmBe Soure Region #(( ):& ( ):( ):& ( ):( )) imp:n=1 imp:p=1 $void spring area (-301 2):(3-301) imp:n=1 imp:p=1 $SS304 Shell ( ):( ):& ( ):( ):& ( ) imp:n=1 imp:p=1 ** Fe Sphere ** e #( ) & #( ) & #( ) & #( ) & #( ) & #(( ):( & )) & #(( ):( & )) & #( ) & #( ) & #(-533:( )) & #(-534:( )) & #( ) & #( ) & #( ) imp:n=1 imp:p=1 $air from Fe surfae to tally sph e imp:n=1 imp:p=1 $air imp:n=1 imp:p=1 $void from sphere to edge of univ (303:309) (305:311) (310:304) (308:-311) & imp:n=1 imp:p=1 $Fe sphere imp:n=0 imp:p=0 $Void spae outside universe imp:n=1 imp:p=1 $plugged right tube e #( ) imp:n=1 imp:p=1 $left tube ( ):( ) & imp:n=1 imp:p=1 $plugged bottom tube imp:n=1 imp:p=1 $plugged top tube imp:n=1 imp:p=1 $smaller plug for left tube ** Air to ombine for Fe Sphere ** e imp:n=1 imp:p=1 $air/styrofoam from soure to sphere ** ** Fe Stand ** imp:n=1 imp:p=1 $base plate imp:n=1 imp:p=1 $l upp base imp:n=1 imp:p=1 $r upp base imp:n=1 imp:p=1 $l support imp:n=1 imp:p=1 $r support ( ):( & ) imp:n=1 imp:p=1 $left support ap ( ):( & ) imp:n=1 imp:p=1 $right support ap imp:n=1 imp:p=1 $left ap ring imp:n=1 imp:p=1 $right ap ring :( ) imp:n=1 imp:p=1 $left eyelet :( ) imp:n=1 imp:p=1 $right eyelet imp:n=1 imp:p=1 $left flange imp:n=1 imp:p=1 $right flange ** Surfae Cards 301 SO $Outer surfae of soure sphere 2 SO $Inner Radius of SS304 Layer 3 PZ $Upper Bound on AmBe Material 4 PZ $Upper Bound on Void Spae 119

133 5 PZ $Lower Bound on Void Spae 63 C/Y $leaf spring middle irle outer 64 C/Y $leaf spring left irle outer 65 C/Y $leaf spring right irle outer 66 C/Y $leaf spring middle irle inner 67 C/Y $leaf spring left irle inner 68 C/Y $leaf spring right irle inner 71 PZ $end spring l/r 72 PY $edge of width of spring 73 PY 1.27 $edge of width of spring 74 PX $used to treat inner half of small urve different for utoffs 75 PX $used to treat inner half of small urve different for utoffs 76 PZ 0.01 $used to fix what 75 does in allowing top of irles 77 p p **Fe Sphere ** 355 SO 38.1 $outer surfae of Fe Sphere 306 SO 500 $Edge of the Universe 302 SO 7.62 $inner void for soure 303 CX $onstant radius tube from left 304 PY $plane to define radius hange point in bottom entry 305 CY 5.08 $tube from bottom (smaller radius) 310 CY 6.35 $tube from bottom (larger radius) 307 C/Y $tube on right side 308 CY 1.27 $used to define upper half for plug geometries 309 PX 0 $used to stop tubes on left/right of origin 311 PY 0 $used to stop tubes on top/bottom of origin 312 PX $top of shape used to move left plug out due to Cf attahment 313 PX $bottom of left plug ylinder 314 CX 4.25 $smaller left plug 322 SO 100 $100m Sphere around soure ** **Fe Stand** 501 PZ $bottom of base plate 502 PZ $top of base plate and bot of upper base 503 PY $top edge of base plate 504 PY $bottom edge of base plate 505 PX $left edge of base plate and upper base 506 PX $right edge of base plate and upper base 507 PZ $top of upper base 508 PY $top edge of upper base 509 PY $bot edge of upper base 510 PX $right edge of l upper base 511 PX $left edge of r upper base 512 P P PX $left support left edge 515 PX $right support left edge 516 PX $left support right edge 517 PX $right support right edge 518 PZ 0 $supports top edge 519 PZ $ap srew flange top 520 PY $ap left vert 521 PY $ap right vert 522 P $ap left diagonal 523 P $ap right diagonal 524 PZ $ap top 525 PY $ap left edge 526 PY 12.7 $ap right edge 527 CX $inner radius ap ring {set to math port radius} 528 CX $outer radius ap rin 529 PX $outer edge of left ap ring 530 PX $outer edge of right ap ring 531 PX $inner edge of left ap ring {adjusted to fit imperfet sphere} 532 PX $inner edge of right ap ring {adjusted to fit imperfet sphere} 533 TX $left eyelet 534 TX $right eyelet 120

134 535 C/Z $left eyelet onnetor walls 536 C/Z $right eyelet onnetor walls 537 PZ 12.7 $eyelet onnetor top utoff 538 PY $bottom edge of flagnes 539 PY.635 $top edge of flanges 540 PZ $top of flanges (tapered ompletely off) 541 P P ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards m $AmBe SS304 m & ** Fe Sphere ** m & ** m $air ** Soure sdef par=1 erg=d1 RAD=D2 CEL=1 SI1 4.14e & & & & & & & sp & & & & & & & & & sb R 121

135 SI SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS & gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E

136 1.99E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 123

137 B.12 AmBe in Tantalum MCNP Input AmBe in 12 m r Ta sphere Cell Cards (-2-3 4):(-2-5) imp:n=1 imp:p=1 $AmBe Soure Region #(( ):& ( ):( ):& ( ):( )) imp:n=1 imp:p=1 $void spring area (-1 2):(3-1) imp:n=1 imp:p=1 $SS304 Shell leaf spring - enter:left:far left:right:far right ( ):( ):& ( ):( ):& ( ) imp:n=1 imp:p=1 ** Ta Sphere ** e-3 ( #(( ):( ):& ( ):& ( ):& ( ):( ):& (( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ):( ))& :(( ))& ))& :(-308 #( ) & #( )):-309 & imp:n=1 imp:p=1 $air from Ta surfae to tally sphere e imp:n=1 imp:p=1 $air from sphere to edge of universe imp:n=1 imp:p=1 $Ta Sphere imp:n=0 imp:p=0 $Void spae outside universe imp:n=1 imp:p=1 $aluminum ring 1 (in groove) ( ):( ):& ( ):& ( ) imp:n=1 imp:p=1 $aluminum ring imp:n=1 imp:p=1 $aluminum ring 3 * Al table top* imp:n=1 imp:p=1 $Al table top ( ):( ) & imp:n=1 imp:p=1 $bl leg ( ):( ) & imp:n=1 imp:p=1 $br leg ( ):( ) & imp:n=1 imp:p=1 $tl leg ( ):( ) & imp:n=1 imp:p=1 $tr leg ( ):( ) & imp:n=1 imp:p=1 $bl thik leg ( ):( ) & imp:n=1 imp:p=1 $br thik leg ( ):( ) & imp:n=1 imp:p=1 $tl thik leg ( ):( ) & imp:n=1 imp:p=1 $tr thik leg imp:n=1 imp:p=1 $Al stabilizer ring ** Surfae Cards 1 SO $Outer surfae of soure sphere 2 SO $Inner Radius of SS304 Layer 3 PZ $Upper Bound on AmBe Material 4 PZ $Upper Bound on Void Spae 5 PZ $Lower Bound on Void Spae 63 C/Y $leaf spring middle irle outer 64 C/Y $leaf spring left irle outer 124

138 65 C/Y $leaf spring right irle outer 66 C/Y $leaf spring middle irle inner 67 C/Y $leaf spring left irle inner 68 C/Y $leaf spring right irle inner 71 PZ $end spring l/r 72 PY $edge of width of spring 73 PY 1.27 $edge of width of spring 74 PX $used to treat inner half of small urve different for utoffs 75 PX $used to treat inner half of small urve different for utoffs 76 PZ 0.01 $used to fix what 75 does in allowing top of irles 77 p $diagonal to fit two urves of spring at tangent 78 p $diagonal to fit two urves of spring at tangent **Ta Sphere ** 301 SO $Outer surfae of soure sphere 306 SO 500 $Edge of the Universe 307 SO 12 $radius of Ta spherial shell 308 tz $top groove 309 tz $bottom groove 322 SO 100 $100m Sphere around soure 310 z 11.7 $Al ring inner radius in groove 313 z 14.1 $Al ring outer radius (all) 311 pz.9 $top of Al ring in groove 312 pz.6 $bottom of Al Ring in groove / top of ring z 12.1 $Al ring inner radius (ring 2/3) 315 pz.3 $bottom of ring 2 / top of ring pz 0 $bottom of ring py 1.9 $top of lift arms 318 py -1.9 $bot of lift arms 319 C/Z $l round edge of lift arm 320 C/Z $r round edge of lift arm 360 px 32.7 $utoff of straight part of lift arm 361 px $utoff of straight part of lift arm *Al table top* 501 pz $top of Al table top 502 pz $bot of Al table top 503 px $left of Al table top 504 px $right of Al table top 505 py $front of Al table top 506 py $bak of Al table top 513 px $left of Al table leg 514 px $right of Al table leg 515 py $front of Al table leg 516 py $bak of Al table leg 523 px $utoff of Al table top 524 px $utoff of Al table top 525 py $utoff of Al table top 526 py $utoff of Al table top 531 pz $bot of thin legs/top of thik legs 543 px $left of Al table thik leg 544 px $right of Al table thik leg 545 py $front of Al table thik leg 546 py $bak of Al table thik leg 551 z 6.25 $inner radius of Al stabilizer 552 z 8.75 $outer radius of Al stabilizer 553 pz $top of Al stablizer ** The next set of planes will be used to segment surfae 22 to do the angular dependent tally. They do not have to be used in the ell desriptions. 324 PZ PZ PZ PZ PZ PZ PZ PZ PZ

139 333 PZ PZ PZ PZ PZ PZ PZ PZ PZ PZ ** Material Cards m $AmBe SS304 m & ** Ta Sphere ** m $Ta m $Al ** m $air ** Soure sdef par=1 erg=d1 RAD=D2 CEL=1 SI1 4.14e & & & & & & & sp & & & & & & & & & sb R SI SP Tallies F2:N 322 FC2 Neutron Flux FS T $plus/minus 15.6m utoffs Current Tally of whole sphere F1:N 322 FC1 number of neutrons per spherial surfae segments at 100 m Segmented Tally aross z plans of the sphere FS & F12:N 322 FC12 Irp 74 ambient dose equivalent on spherial surfae at 100 m Segmented Tally aross z plans of the sphere FS &

140 gamma fluene tally at 100 m F22:P 322 FC22 Gamma Ray Fluene indued by neutrons at 100 m FS T $plus/minus 15.6m utoffs F32:P 322 FC32 Gamma Ray Dose rate at 100 m FS T $plus/minus 15.6m utoffs F5:N FC5 Point Neutron Detetor at 100m F25:N FC25 ICRP 74 ambient dose equivalent on Point Neutron Detetor at 100m Energy groups used to bin fluene e1 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e2 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e5 1.00E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E e E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E for gammas e

141 ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 Dose Conversion oeffients DE E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 DF ICRP 74 DCCs for photons (psv-m2) de df mode n p CUT:N 1J 1.e-10 CUT:P 1J 0.01 nps 1E7 128

142 APPENDIX C: COMPARISON OF 252 Cf SOURCE SPECTRA WITH AND WITHOUT STYROFOAM SPHERE 129

143 Figure C.1. Comparison of 252 Cf Soure Spetra from MCNP with and without Styrofoam Sphere 130

144 APPENDIX D: ISO 8529 NEUTRON FLUENCE SPECTRA FOR SOURCES 131

145 Table D.1. Values of neutron fluene at 1 meter per logarithmi energy interval for a 252 Cf spontaneous fission soure (derived from Table A.1 of referene [22]) Energy Bin top (MeV) 4.14E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+00 neutrons/m^2/s/lethargy 1.07E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

146 Table D.1. Continued 9.00E E E E E E E E E E E E E E E E E E-02 Table D.2. Values of neutron fluene at1 meter per logarithmi energy interval for an AmBe (α, n) soure (derived from Table A.1 of referene [22]) Energy Bin top (MeV) neutrons/m^2/s/lethargy 4.14E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

147 134 Table D.2. Continued 5.25E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+00

148 APPENDIX E: SAMPLE BUMS OUTPUT WITH REMARKS 135

149 Figure E.1. Sample BUMS output with remarks 136