IAEA-TECDOC-CD Intercomparison of Measurements of Personal Dose Equivalent Hp(10) in Photon Fields in the West Asia Region

Transcription

1 IAEA-TECDOC-CD-1567 Intercomparison of Measurements of Personal Dose Equivalent Hp(10) in Photon Fields in the West Asia Region August 2007

2 IAEA SAFETY RELATED PUBLICATIONS IAEA SAFETY STANDARDS Under the terms of Article III of its Statute, the IAEA is authorized to establish or adopt standards of safety for protection of health and minimization of danger to life and property, and to provide for the application of these standards. The publications by means of which the IAEA establishes standards are issued in the IAEA Safety Standards Series. This series covers nuclear safety, radiation safety, transport safety and waste safety, and also general safety (i.e. all these areas of safety). The publication categories in the series are Safety Fundamentals, Safety Requirements and Safety Guides. Safety standards are coded according to their coverage: nuclear safety (NS), radiation safety (RS), transport safety (TS), waste safety (WS) and general safety (GS). Information on the IAEA s safety standards programme is available at the IAEA Internet site The site provides the texts in English of published and draft safety standards. The texts of safety standards issued in Arabic, Chinese, French, Russian and Spanish, the IAEA Safety Glossary and a status report for safety standards under development are also available. For further information, please contact the IAEA at P.O. Box 100, A-1400 Vienna, Austria. All users of IAEA safety standards are invited to inform the IAEA of experience in their use (e.g. as a basis for national regulations, for safety reviews and for training courses) for the purpose of ensuring that they continue to meet users needs. Information may be provided via the IAEA Internet site or by post, as above, or by to Official.Mail@iaea.org. OTHER SAFETY RELATED PUBLICATIONS The IAEA provides for the application of the standards and, under the terms of Articles III and VIII.C of its Statute, makes available and fosters the exchange of information relating to peaceful nuclear activities and serves as an intermediary among its Member States for this purpose. Reports on safety and protection in nuclear activities are issued in other publications series, in particular the Safety Reports Series. Safety Reports provide practical examples and detailed methods that can be used in support of the safety standards. Other IAEA series of safety related publications are the Provision for the Application of Safety Standards Series, the Radiological Assessment Reports Series and the International Nuclear Safety Group s INSAG Series. The IAEA also issues reports on radiological accidents and other special publications. Safety related publications are also issued in the Technical Reports Series, the IAEA-TECDOC Series, the Training Course Series and the IAEA Services Series, and as Practical Radiation Safety Manuals and Practical Radiation Technical Manuals. Security related publications are issued in the IAEA Nuclear Security Series.

3 IAEA-TECDOC-CD-1567 Intercomparison of Measurements of Personal Dose Equivalent Hp(10) in Photon Fields in the West Asia Region August 2007

4 The originating Section of this publication in the IAEA was: Policy and Programme Support Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria INTERCOMPARISON OF MEASUREMENTS OF PERSONAL DOSE EQUIVALENT HP(10) IN PHOTON FIELDS IN THE WEST ASIA REGION IAEA, VIENNA, 2007 IAEA-TECDOC-1567 ISBN ISSN IAEA, 2007 Printed by the IAEA in Austria August 2007

5 FOREWORD In accordance with its statutory function, the International Atomic Energy Agency (IAEA) has been assisting its Member States in establishing and upgrading their radiation protection infrastructures, including activities in occupation radiation protection. Individual external dosimetry services for photon radiation have been under establishment or upgrading with support through the Technical Cooperation Model Projects RAW/9/006, Upgrading Radiation Protection Infrastructure (concluded in 2000), and RAW/9/008, Development of Technical Capabilities for Sustainable Radiation and Waste Safety Infrastructure ( ), in all the participating countries in the West Asia Region. Two regional training courses were organized by the IAEA, in Germany in 1998, on Design, Implementation and Management of Individual Monitoring Services (IMS), and in the Syrian Arabic Republic in 2001, on Assessment of Occupational Exposure due to External Sources, under the above stated projects. However, no performance testing has yet been carried out and no regional intercomparisons have been established before in this region. Only two Member States from the region (the Syrian Arab Republic and Lebanon) participated in the interregional Intercomparison for Individual Monitoring of Radiological Measurements for Purposes of Monitoring Personal Dose Equivalent H p (10) in The IAEA officer responsible for the compilation of this publication was J. Zeger of the Division of Radiation, Transport and Waste Safety.

6 EDITORIAL NOTE The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA.

7 CONTENTS 1. INTRODUCTION PROJECT SETUP Objectives Scope of the intercomparison Project design Performance requirement SELECTED IRRADIATION FACILITIES Standards in protection level SSDL in the Syrian Arab Republic SSDL in the Islamic Republic of Iran Irradiation process SELECTION OF PARTICIPANTS SCHEDULE OF THE INTERCOMPARISON Phase I Performance testing intercomparison Phase II Mixed photon qualities intercomparison INTERCOMPARISON RESULTS Results discussion by radiation quality Results discussion by outliers Results discussion by distribution CONCLUSIONS Participation Organization Results of the intercomparison REFERENCES ANNEX I. ANNEX II. NOMINATION FORM AND QUESTIONNAIRE FOR PARTICIPATING LABORATORIES DOSES AND CONDITIONS TO BE DELIVERED BY IRRADIATING LABORATORIES ANNEX III. PARTICIPANTS ANNEX IV. TECHNICAL INFORMATION ABOUT THE PARTICIPATING LABORATORIES ANNEX V. GRAPHICAL PRESENTATION OF THE RESULTS CONTRIBUTORS TO DRAFTING AND REVIEW... 91

8

9 1. INTRODUCTION In the early 1980s, the International Atomic Energy Agency (IAEA) started the organization of intercomparisons for different purposes in the occupational radiation protection area. While the first intercomparison focused on the impact of the possible adoption of the new set of operational quantities introduced in the International Commission on Radiation Units and Measurements (ICRU) Report 39 [1] in 1985, later intercomparisons focused on the performance of personal dosimetry services mainly for photon radiations. Pursuant to General Conference resolution GC(43)/RES/13, the IAEA is organizing international intercomparisons for monitoring purposes with a view on helping Member States to comply with dose limitation requirements and to harmonize the use of internationally agreed quantities and recommended assessment methods. The resolution encourages all governments to join in the current cooperative efforts directed towards the organization of international intercomparisons relating to radiation dose measurements for the control of occupational and other exposures. During the results meeting of the 1999 Intercomparison for Individual Monitoring of Radiological Measurements for Monitoring Purposes, Personal Dose Equivalent H p (10) the participating laboratories recommended, inter alia, that the IAEA should act as a focal point for the organization of intercomparisons. The IAEA is carrying out a project on harmonization of radiological quantities and units. In this frame a close liaison is established with different organizations, inter alia the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), the International Commission on Radiological Protection (ICRP), ICRU and also with other institutions for intercomparisons of different methods. The IAEA has organized an interregional intercomparison of individual monitoring services (IMS) for determination of H p (10) in mixed neutron-gamma fields ( ) [2] and a regional intercomparison in Latin- America [3] and another one in East Asia for photon fields ( ) [4]. Since 1994, the IAEA has established technical cooperation model projects on upgrading radiation protection infrastructure in which more than 90 Member States, including 12 countries from the West Asia Region, were participating. In particular, under the Thematic Safety Area 2 of the Model Project RAW/9/008 on the establishment of occupational exposure control, the participating Member States have been assisted in establishing individual external monitoring services for dose assessment of radiation workers at a national level. All the participating Member States have in place proper equipment and eleven of them provide such services but they are at various states of operation and competency. The principal rationale in provision of such services in each country is to have an individual monitoring of the exposed work force to meet the requirements of the Safety Guide RS-G-1.3 [5] and the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (the BSS) [6]. To verify the compliance with the performance requirements, there was a need for organizing a regional intercomparison of dosimetry services. This was planned to be a multi-stage intercomparison starting with simple photon qualities and ending with mixed photon qualities in different irradiation conditions including rotational field, simulating real work place conditions. 1

10 2. PROJECT SETUP 2.1. Objectives The overall objective was to verify performance and to improve the Individual Monitoring Services (IMS). This was planned to be achieved with the following specific objectives of the intercomparison: 1. To assess the capabilities of the dosimetry services to measure the quantity H p (10) in photon (gamma and X ray) fields. 2. To help the participating Member States in achieving sufficiently accurate dosimetry service and, if necessary. 3. To provide guidelines for improvements and not simply a test of the performance of the existing dosimetric service Scope of the intercomparison The scope of the intercomparison was aimed for passive dosimeters, which determine the personal dose equivalent H p (10) in photon radiation fields. The following types of dosimeters are commonly used in the region and thus were expected: Thermolumenescence dosimeter (TLD) Film dosimeter 2.3. Project design The objectives mentioned above were reached by an intercomparison, which was performed in two stages: Phase I Irradiation in selected mono-energetic radiation fields (ISO W and S series qualities, one quality with three irradiation angles). The results could be used to verify the calibration and to improve the dosimetric procedures of the participants, if necessary. Phase II Mixed photon qualities intercomparison in different irradiation conditions (ISO W and S series qualities) including rotational field, simulating real work place conditions. Member States nominating services to participate were requested to provide the nomination with the information requested in (Annex I). 2

11 2.4. Performance requirement The response, H pm /H pw, of the dosimeters must meet the following criteria (RS-G-1.3): For pure photon radiation 1 1,5 2H p0 1 H p0 + H pw H H pm pw H p0 1,5 1+ 2H p0 + H pw (2.1) with H pm value measured by the participant, H pw conventional true value stated by the irradiating laboratory, H p0 lower limit of dose range, H p0 = 0,1 msv for whole body dosimeters Fig Limit of the quotient H pm /H pw as function of the conventional true value, H pw using H p0 = 0,1 msv, solid line according to eq. (2.1). 3

12 3. SELECTED IRRADIATION FACILITIES Two IAEA recognized Secondary Standard Dosimetry Laboratory (SSDL)-network members from the West Asia region volunteered to do the irradiation and the distribution of the dosimeters free of charge. The SSDL of the Syrian Atomic Energy Commission in Damascus, Syrian Arab Republic, performed the irradiation with ISO quality and the SSDL of the Atomic Energy Organization of Iran in Karaj, the Islamic Republic of Iran, performed the irradiation with ISO W qualities for both phases I and II Standards in protection level SSDL in the Syrian Arab Republic Electrometer: PTW UNIDOS (10002 #20293) calibrated at manufacturer and IAEA (date of last calibration: Apr. 2002) Ionization Chamber: PTW (LS-01 # 042) calibrated at IAEA for 137 Cs, 60 Co and X ray, (date of last calibration: Feb. 2001) The SSDL did participate in the intercomparisons run by the IAEA/WHO Network of Secondary Standard Dosimetry Laboratories "TLD Postal Quality Audit for Cs-137 Radiation Protection Calibrations in 2000, 2003 and The results were Participants/IAEA air Kerma 0.98, 1.00 and 1.00 respectively SSDL in the Islamic Republic of Iran Electrometer: PTW UNIDOS (10002#20176) calibrated by manufacturer and IAEA (date of last calibration: April 2003) Ionization chamber: PTW (LS-01 #924) calibrated at IAEA for 137 C, 60 Co and X ray qualities (date of last calibration: April 2003) The SSDL did participate in the intercomparisons run by the IAEA/WHO Network of Secondary Standard Dosimetry Laboratories TLD postal quality audit for Cs-137 Radiation protection calibration in 2003 and The last results were: participants/ IAEA 1.00 and Irradiation process The SSDL in the Syrian Arab Republic has performed the irradiation with ISO quality Dosimeters from 21 different laboratories have been irradiated. Distance from the 137 Cs source was 200 cm. Dosimeters have been fixed on a (30x30x15 cm) ISO PMMA Slab Phantom using 0.05 mm adhesive tape (Fig. 3.1). Dosimeters have been irradiated in groups of four placed on the center of the phantom. Dosimeters have been changed manually. The phantom was placed on a Perspex rotating table to get different irradiation angles. The source switched off automatically after the defined irradiation time using a digital timer. 4

13 Fig Irradiation set up in the Syrian Arab Republic with quality using the ISO PMMA Slab Phantom. The SSDL in the Islamic Republic of Iran has performed the irradiation with ISO-W qualities ( and ) at a distance from X ray focal spot F.S.D=300cm Fig Irradiation set up in the Islamic Republic of Iran with W-X ray qualities using the ISO PMMA Slab Phantom. 5

14 4. SELECTION OF PARTICIPANTS All countries in the West Asia region were approached and asked to participate in this intercomparison. 24 Laboratories from 12 countries in the region confirmed their participation (see Annex III). Only 3 laboratories out of 24 did not participate in both phases (namely Lab. 5, 10 and 15). The final number of participating laboratories was 21 and Fig.4.1 shows all types of dosimeters from the participating laboratories. Fig All types of dosimeters irradiated during this intercomparison. 6

15 5. SCHEDULE OF THE INTERCOMPARISON 5.1. Phase I Performance testing intercomparison A total of 11 different irradiation conditions were used. Irradiations were performed on the ISO slab phantom and with parallel or nearly parallel beam conditions to investigate energy and angular dependence and linearity (Annex II). For this stage the participants received the information about which of the dosimeters were irradiated, which ones should be used to measure only environmental background or transport dose; the radiation quality, angles of radiation incidence and one dose value at one of the qualities for reference. After they submitted their complete results to the evaluator, the participants received the target dose values of all irradiations. In this phase each of the participating laboratories were requested to send 13 dosimeters, the first six dosimeters (No.1 to 6) from each service to the SSDL in the Syrian Arab Republic and the last seven dosimeters (No.7-13) to the SSDL in the Islamic Republic of Iran. The SSDL in the Syrian Arab Republic performed the irradiation with ISO quality and the SSDL in the Islamic Republic of Iran performed the irradiation with ISO W qualities ( and ) as scheduled. The irradiated dosimeters were sent back to the participating services for evaluation. The results of the dose evaluation were reported to the project coordinator. To discuss the evaluated results of the first phase and to give all participating laboratories an opportunity to profit from the discussion, a workshop was organized by the IAEA in Vienna after the completion of the first phase from 18 to 19 October The title of this workshop was Results Meeting for the First Phase of the Intercomparison on Measurements of the Quantity Personal Dose Equivalent, H p (10) in Photon Fields. The discussions during the midterm meeting indicated the following results and needs in the region: Generally only few laboratories had some information about type and performance testing of their dosimeters, fewer still had done the tests themselves. Many reported that the suppliers were reluctant to provide type testing reports or results and that the services had to put on heavy pressure to get information. Participants asked for a checklist of questions to be posed to the equipment suppliers to get enough information about the type testing.(this was given to all participants in a separate document during the meeting). The calibration situation, especially calibration to read the dose equivalent quantity H p (10), is far from ideal. Not every country has a SSDL service, the access to foreign services seems not to be easy all the time. Some countries even do the calibration by irradiation with a 90 Sr-source built in to the reader workstation, which is not foreseen for this purpose. The incorporation of correction factors like element correction coefficients, fading, PMT noise and heating rate, into the final result is not standard practice with all services. 7

16 Although two training courses on how to run an external dosimetry service were delivered to the region in 1998 and 2001, there is a clear need to repeat such courses as the staff of the laboratories in the region changes. Quality management is not yet an issue for many laboratories. But the need for it is well recognized and some representatives, especially from the Islamic Republic of Iran and Saudi Arabia asked the IAEA to provide training and guidance in this topic. The participants were informed that training packages are ready for that purpose. The participants were offered guidance, training and advice in matters of accreditation. The act of accreditation itself is not within the scope of IAEA s statute and the participants, although they wanted the IAEA to act as a accreditation service for laboratories voluntarily participating, were directed towards the national accreditation agencies Phase II Mixed photon qualities intercomparison A total of 12 different irradiation conditions were used in this phase (Annex II). Irradiation was performed on the ISO slab phantom and with parallel or nearly parallel beams. For this stage the participants received the information which of the dosimeters were irradiated and which should be used only to measure environmental background or transport dose. No further information on photon dose, quality and angle of radiation incidence were given. After they submitted their results to the evaluator, participants received the target dose values and the irradiation conditions of all irradiations for their own evaluation of their results. In this phase each of the participating laboratories was requested to send 14 dosimeters. The first six dosimeters (No. 1 to 6) from each service were sent to the SSDL in the Syrian Arab Republic and the last eight dosimeters (No.7 to 14) to the SSDL in the Islamic Republic of Iran. The SSDL in the Syrian Arab Republic performed the irradiation with ISO quality and the SSDL in the Islamic Republic of Iran performed the irradiation with ISO W qualities and the mixed qualities (, and W-250) as scheduled. The irradiated dosimeters were sent back to the services for assessment. The results of the dose evaluation were sent to the project coordinator. The results were analyzed and are presented in this final report. 8

17 6. INTERCOMPARISON RESULTS This intercomparison focused on the performance of personal dosimetry services for external occupational exposure and was meant to help the participating Member States in achieving sufficiently accurate measurement results. The main criterion for stating compliance with the performance requirements was the acceptability of measurement results through the trumpet curve as established in equation 2.1 (chapter 2.4). Any results, not contained within the acceptability band of the trumpet curve were regarded as outliers and as indicators that the dose assessment method or the calibration of the instruments used needed improvement. For the dose region from 1 msv up, which was mainly used in this intercomparison, the limits of the trumpet curve have been approximated by a response, in comparison to the delivered radiation dose, of 0.66 as lower limit and 1.5 as upper limit Results discussion by radiation quality For radiation quality and 0 degree incidence angle the results were generally very good for all the doses used (1, 4 and 14 msv). Only two laboratories showed distinctive underestimation of dose (Fig. 6.1.). 0 degree irradiation Response upper acceptance limit Target value lower acceptance limit msv 4 msv 14 msv Lab ID Fig Response factors for irradiation with 0 degree incidence angle. 9

18 For this radiation type, which was used in Phase I of the intercomparison, the participants were informed about the dose delivered to one dosimeter to give them a chance to check their calibration and the performance of their reading instruments. Some laboratories did not take this opportunity to recalibrate their measurement equipment using the reported dose and, consequently, did not show improved results in the second phase. For the same radiation type (), but coming from 30 and 60 degrees incidence angle, the results also were mainly within the trumpet curve. A slightly larger trend of underestimation might be seen with this angled incidence (Fig. 6.2.). lower acceptance limit 4 msv angle irradiation upper acceptance limit Response lower acceptance limit degree angle 60 degree angle Lab ID Fig Response factors for irradiation with 30 and 60 degree incidence angle. Few laboratories with clear trends in their data were advised to recalibrate their TLD system or reorganize their method of readout. Acting on this advice, some laboratories have shown visible improvement in the second phase either by reduction of the number of outliers or through improved quality of the reported results or in both. However, two laboratories have shown grave and unexplainable deterioration of their results in the second phase compared with the first one. This is visible in the results of the rotational irradiation, again using quality, but varying the incident angle from -60 to +60 degrees, as it was done in the second phase of the intercomparison. Excluding the, above mentioned, two laboratories, all results were within the trumpet curve and the trend had moved to slight overestimation of the dose (Fig. 6.3.). 10

19 -60 to +60 degree irradiation upper acceptancelimit Response lower acceptance limit msv 3 msv 10 msv Lab ID Fig Response factors for irradiation with incidence rotating from -60 to +60 degrees. Regarding the X ray qualities, which also were used at 0 degrees incidence during the first phase of the intercomparison, the distribution of the results is very different compared to the -quality. Especially the radiation, which has a main energy of 57 kev, posed a big problem to the participants. The general trend was to large overestimations of the dose (Fig. 6.4.). The higher energy radiation (Fig. 6.5.), with a main energy of 208 kev, did not pose a similar problem to the participants. This radiation, again at 0 degree incidence, was generally well assessed. The trend included more underestimation than with the quality. Some laboratories reported unexpected high outliers, which could not be easily explained in view of the results for the quality. 11

20 0 degree irradiation upper acceptance limit Response lower acceptance limit msv 4 msv 14 msv Lab ID Fig Response factors for irradiation with 0 degree incidence. 0 degree irradiation upper acceptance limit Response lower acceptance limit Lab ID 1 msv 4 msv 14 msv Fig Response factors for irradiation with 0 degree incidence. 12

21 In the second phase of the intercomparison, emphasize was placed on simulated workplace radiation fields by using mixtures of gamma and X ray irradiations and applying the radiation from many different angles (rotational radiation fields). The problem posed by combining radiation with X rays at 0 degree incidence resulted in a wide spread of reported results (Fig. 6.6). By comparing the results to the pure components (Fig for and Fig for ) a dominant influence by the response to is visible. The added X ray component to the irradiation spectrum clearly leads to more underestimation of the delivered dose than with the pure irradiation. + 0 degree irradiation upper acceptancelimit Response lower acceptance limit msv 3 msv 10 msv Lab ID Fig Response factors for and combined irradiation with 0 degree incidence. The results were consistent for all applied doses with only the low dose of 0.8 msv, which is encountered very often in every day application of occupational exposure monitoring, giving more problems to some participants. The same radiation combination of and was also tested on a rotational incidence basis, changing the incidence angle from -60 to +60 degrees (Fig. 6.7.). As this test was done with a delivered dose of 5 msv, there were no problems for a larger number of participants to report results within the acceptance limits of the trumpet curve. 13

22 + -60 to +60 degree irradiation upper acceptancelimit Response lower acceptance limit msv Lab ID Fig Response factors for combined and irradiation with incidence rotating from -60 to +60 degrees. The final test in Phase II of the intercomparison was performed with the X ray quality W-250 (main energy 137 kev), again on a rotational basis. W to +60 degree irradiation upper acceptance limit Response lower acceptance limit msv 3 msv Lab ID Fig Response factors for W-250 irradiation with incidence rotating from -60 o to +60 o Results discussion by outliers Comments and remarks from the comparative graphical presentation of the results shown in the previous chapter are summarized in Table

23 Table 6.1. Outlier distribution in both phases First phase Second phase Second phase Improvement without ID13,14 under estimation % over estimation % sum % Table 6.1 shows that, excluding the results of the second phase for Lab.13 and Lab.14 (all the points are suddenly outliers, without any obvious explanation), the number of outliers between first and second phase would have decrease from 32 to 9. This indicates quite good improvement during this intercomparison. The overall results of both phases for 450 reported TLD readings (excluding Lab 13 and 14 in the second phase) show a total of 41 outliers or 9.1 %. Even if the unexplainable results of Labs 13 and 14 were included, it would be 59 outliers out of 469 points or 10.9 %. The overall improvement of more than 70 % shown in Table 6.1 emphasizes the importance of participating in intercomparisons for all laboratories. More specific information for each individual participating laboratory showing improvement possibilities are given in Table 6.2. Tables 6.3 and 6.4 expand this information with remarks to the laboratories, which could be used for quality improvement programs. Table 6.5 details the result for the irradiation qualities used, showing the main problems in irradiations, especially with low doses. Finally Table 6.6 shows the total of the outlier evaluation. 15

24 Table 6.2. Laboratory rating on outliers First phase Second phase Lab. ID Outliers under estimation Outliers over estimation Rating Outliers under estimation Outliers over estimation Rating Improvement g 0 0 e i 0 0 e 3 not reported not reported not rated g 0 0 e not reported not reported not rated e 0 0 e g 0 3 g g 0 0 e i 0 0 e e 1 0 i g 0 0 e e 10 0 i! g 5 3 i! i 0 2 g e 0 0 e i 0 0 e g 0 0 e e 0 0 e e 0 0 e i 3 0 i e 0 0 e e 0 0 e sum under estimation over estimation under estimation over estimation Rating no outliers e excellent only overestimation g good underestimation i improvement urgently necessary 16

25 Table 6.3. Summary result of the outlier evaluation sum without ID13,14 sum outliers in second phase first phase second phase 27 9 both phases Rating first phase second phase no outliers excellent % % only overestimation good % 2 9.5% under estimation improvement urgently necessary % % Table 6.4. Individual results of each laboratory Lab Number of outliers Remarks ID Phase I Phase II Consistently good results. Even improvement between phase I and II in the number of outliers (1 to 0) Improvement between phase I and II in the number of outliers (1 to 0) and the mean value of the response (0.63 to 1.18). Reported only high-dose values of X ray qualities and. Outlier at 4 msv. 3 not Did not participate in phase I. 0 reported The result in phase II were excellent. 4 3 not Did not participate in phase II. All outliers in phase I are due to reported X ray quality (overestimation up to 88%). 5 Choose not to participate at all Excellent results in both phases. Underestimation by 30% in, 1mSv, straight Slight improvement. General overestimation by 42%. Bad accuracy in the low dose range, all outliers are due to doses up to 1 msv Improvement between phase I and II in the number of outliers (1 to 0). General overestimation in the X ray qualities (up to 53% for ) Improvement between phase I and II in the number of outliers (1 to 0). General underestimation in the X ray qualities (20% for ) 10 Choose not to participate at all. 17

26 Lab Number of outliers Remarks ID Phase I Phase II Excellent results in phase I. Slightly less so in phase II. Had a near miss in W-250, 3 msv, rotational. Maybe reader needs checking. Very good improvement between phase I and II in the number of outliers (3 to 0). All outliers in the first phase are due to overestimation in the X ray quality up to 81%. Excellent result in phase I, although a tendency to underestimation is obvious. Grave deterioration in phase II, as all of the points were outliers. However, consistency in the underestimation of 67% and good precision (one of the lowest SD = 8%) indicate that this underestimation is due to using the wrong calibration factor for the TLD reader. Good result in phase I (only overestimation for all reported values). Grave deterioration in phase II as all of the points were outliers. However, no consistency or precision some points have underestimation and most points have overestimation by up to 13 times. This can not be attributed to using the wrong calibration factor for the TLD reader. 15 Choose not to participate at all Slight improvement from phase I to phase II as underestimation by 22% in the first phase change to overestimation by 45% is the second phase. This could have been a change in calibration that was overdone. Excellent results in both phases. overestimation by 27% in Very good improvement. It was pointed out to the Laboratory in the midterm workshop that due to the good precision (one of the lowest SD = 7%), the 9 outliers are probably attributable to a wrong calibration factor for the TLD reader. The Lab. recalibrated the system and the results of phase II were excellent Improvement between phase I and II in the number of outliers (3 to 0). A good result was turned into excellent. Slightly less overestimation in second phase. All outliers in first phase were due to (overestimation by more than 100%) Excellent results in both phases. Overestimation by 22% in Excellent results. Consistent overestimation 14% and 10% in first and second phase. Overestimation by 32% in No improvement. No visible trend except for the average overestimation by 20% in. Grave underestimation in higher dose X ray qualities Excellent results in both phases. Good improvement in the mean value of response (0.92 to 0.97) underestimation by 27% in Excellent results. Consistent overestimation 13% in both phases. Overestimation up to 39% in. 18

27 Table 6.5. Statistic evaluation per radiation quality Response Phase I reported / delivered 1 msv 4 msv 14 msv 4 msv 4 msv angle 0 degree 0 degree 0 degree 30 degree 60 degree Max Min Average under estimation over estimation msv 4 msv 14 msv 1 msv 4 msv 14 msv angle 0 degree 0 degree 0 degree 0 degree 0 degree 0 degree Max Min Average under estimation over estimation angle 0.5 msv 0 degree 0.8 msv rotational -60 to +60 degrees 3 msv 10 msv Max Min Average under estimation over estimation

28 Response Phase II reported / delivered msv + 3 msv + 10 msv angle 0 degree 0 degree 0 degree + 5 msv rotational -60 to +60 degrees W msv W msv Max Min Average under estimation over estimation Table 6.6. Total outlier results Phase I under over sum estimation estimation outliers X ray (different qualities) Phase II X ray (partly + ) Results discussion by distribution Figure 6.9 presents the mean value (of the responses -1) for the participating laboratories in phase I for the radiation quality arranged from largest underestimation to the largest overestimation together with the standard deviation for the results in each laboratory (Lab. 3 did not participate in phase I and Lab. 14 did not send the results for the quality irradiation). It can be seen in this figure that most laboratories assessed the doses within 25% over- or underestimation. Only three laboratories (Lab 7, 18 and 19) had over- or underestimation by more than 25%. The standard deviation for all laboratories was within 12%, except for Labs 7 and

29 Mean value of responses in the first phase C-Sc First phase C-Sc (The mean value of responses -1) Standard deviation of the mean Laboratory ID Fig The mean value of the responses -1 for the participating laboratories in phase I for the radiation quality. It can be seen from Fig and 6.11 that the performance at quality was better than for the radiation, only six labs were out of the 25% over or underestimation. Figure 6.10 shows that the mean values (of the responses-1) for the participating laboratories in the first phase for the radiation quality were not as good as that for the quality. Only 10 laboratories assessed the doses within 25%, two laboratories had under estimation by more than 25% and eight had overestimation by more than 25%. This indicates an overestimation problem in assessing the doses at this quality (as seen in the number of the outliers discussed earlier). 21

30 Mean value response in the first phase First phase (The mean value of responses -1) Standard deviation of the mean Laboratory ID Fig The mean value of the responses -1 for the participating laboratories in the first phase for the radiation quality. Mean value response in the first phase First phase (The mean value of responses -1) Standard deviation of the mean Laboratory ID Fig The mean value of the responses -1 for the participating laboratories in the first phase for the radiation quality. 22

31 The overall response in the first phase for all the qualities together as shown in Fig.6.12 to 6.14 indicates that only five labs were out the 25% criterion. This number decreases to only three labs in the second phase excluding lab.14. Mean value response in the first phase First phase all qualities (The mean value of responses -1) Standard deviation of the mean Laboratory ID Fig The mean value of the responses -1 for the participating laboratories in the first phase for all the radiation qualities together. 23

32 Mean value response in the second phase Second phase all qualities (The mean value of responses -1) Standard deviation of the mean Laboratory ID Fig The mean value of the responses -1 for the participating laboratories in the second phase for all the radiation qualities together. Mean value response in first and second phase First phase all qualities (The mean value of responses -1) Second phase all qualities (The mean value of responses -1) Laboratory ID Fig The mean value of the responses -1 for the participating laboratories in the first and the second phase for all the radiation qualities. 24

33 Combining the different graphical presentations into one, Fig shows the minima and maxima of the reported results in comparison to the limits of the trumpet curve in the relevant dose region First phase Second phase 2.00 Response Target value straight 1 msv straight 4 msv straight 14 msv 30 degree angle 4 msv 60 degree angle straight 4 msv 1 msv straight 4 msv straight straight straight straight 14 msv 1 msv 4 msv 14 msv straight 0.5 msv rotational 0.8 msv rotational 3 msv rotational straight + 10 msv 0.8 msv straight + 3 msv straight + 10 msv rotational rotational + W msv 5 msv rotational W msv Average Min Max Trumpet low acceptance Trumpet high acceptance Fig Reported responses in relation to target value and acceptance levels of the trumpet curve The graphic shows that there are reported results below the lower acceptance limit for all radiation qualities. The underestimation of the lowest results sometimes is dramatic and could result in grave impact on individuals working according to these dose evaluations. Overestimation, although also clearly present, does not seem to be a similar problem. The results for generally are good, showing mainly acceptable overestimation. Problems are only encountered in the pure X ray and simulated workplace fields. Here more work needs to be done for the evaluation of the X ray component regardless of the radiation energy. 25

34 7. CONCLUSIONS 7.1. Participation Individual external dosimetry services for photon radiation have been under establishment and improvement with IAEA Technical Cooperation support in all the participating countries in the West Asia Region. Two regional training courses were organized by the IAEA covering Assessment of Occupational Exposure due to External Sources. However, only two Member States from the region participated in the inter-regional intercomparison 1999.Therefore, there was a strong need in the region for establishing such intercomparisons with IAEA support. The overall objective of this intercomparison was to verify performance and to improve the service quality for all states in the region. 21 Laboratories from 12 countries in the (former) IAEA/TC West Asia region participated in this intercomparison Organization The intercomparison was performed in two stages: Phase I Irradiation in selected fields (ISO W and S series qualities, one quality with three irradiation angles). The results will be used to verify the calibration and to improve the dosimetric procedures of the participants, if necessary. Phase II Mixed photon qualities intercomparison in different irradiation conditions (ISO W and S series qualities) including rotational field, simulating real work place conditions. A mid term meeting to discuss the results of the first phase was held from 18 to 19 October 2004 at the IAEA, Vienna, Austria under the title Results Meeting for the First Phase of the Intercomparison on Measurements of the Quantity Personal Dose Equivalent Hp(10) in Photon Fields. The outcome of this meeting was very important for some laboratories, as they got information on improvement possibilities for the next and second phase of the intercomparison, which was presenting simulated workplace fields. Some laboratories could take up the improvements and contributed to the overall improvement of the results during the second phase over the first phase Results of the intercomparison It can be concluded from this intercomparison that: The number of outliers between first and second phase have decreased from 32 to 9 (27). The overall results of both phases show a total of 59 outliers out of 469 reported readings making the percentage of outliers 10.9 %. The number of laboratories with no outliers in both phases is only six (Lab ID-6, 17, 20,21,23 and 24). 26

35 The number of laboratories with no outliers in the first phase is 8 and in the second phase is 14 indicating quite good improvement. The number of laboratories with no or only one outlier (criterion for successful laboratory) is 14 in the first phase and 16 in the second phase % of all laboratories fulfil the performance requirement in the firs phase and 76.1% in the second phase indicating considerable improvement. Some participants show a significant over and/or under estimation of the dose values. Of all the outliers in phase I, 25 were due to the X ray qualities (18 due to and 7 due to ) and only 7 due to quality. This pronounced difference for different radiation qualities indicate that a number of laboratories show a distinct energy dependence. The results of the analysis of the mean value and the standard deviation for the results of each of the participating laboratories (for each of the radiation qualities in phase I and for all qualities in phase I and II, and the mean of both phases) indicate that: there are no pronounced differences in the qualities and or in the qualities used in phase II. The main problem is the radiation quality, where, on average, 20% overestimation is reported by participating laboratories. This could be due to participating laboratories inability to correctly assess the doses in the quality (backscattering effect during irradiation of the dosimeter on the body or phantom not taken into account). No visible angular response was found. No pronounced linearity problems were found in general. Some laboratories show a distinct linearity problem in the low dose range. The intercomparison showed the necessity for a support to the personal dosimetry service providers in the region. During the discussion of the first phase results by most of the participants it was possible to assess improvement possibilities for individual laboratories. The participants also emphasized the need for a continuous effort in providing either intercomparisons or at least test irradiation services to the region. All the irradiations have been performed by facilities situated in the region, which could provide similar services more often in locally organized intercomparisons. This could finally lead to a self-supporting regional testing arrangement with decreasing necessity of IAEA involvement. Technically the main problem of, sometimes large, underestimation of monitoring results has to be addressed in the near future. Mainly X ray qualities were giving rise to these problems, more so at low doses. Operational problems in some laboratories, which were newly established before the intercomparison or had their equipment partly out of order (out of calibration), should be tackled by direct training in the lab done by experts. Scientific visits or trainee-ships could also help solve the problem by sending the technicians from the region into well established dose monitoring laboratories. Finally another regional intercomparison in about five years time could give information about further improvements to the services in the region. 27

36

37 REFERENCES [1] INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Determination of dose equivalents resulting from external radiation sources, MD ICRU Publications, ICRU Report 39, Bethesda, (1985) [2] INTERNATIONAL ATOMIC ENERGY AGENCY, Intercomparison on measurements of the quantity personal dose equivalent Hp(d) in mixed (neutrongamma) fields An IAEA Project, Proceedings of the European workshop on individual monitoring of ionising radiation (IM2005) Vienna April 2005, Radiat. Prot. Dosim., IAEA, Vienna (in press). [3] INTERNATIONAL ATOMIC ENERGY AGENCY, Results of the Regional Intercomparison Exercise for the Determination of Operational Quantity Hp(d) in Latin America, Proceedings of the European workshop on individual monitoring of ionising radiation (IM2005) Vienna April 2005, Radiat. Prot. Dosim. IAEA, Vienna (in press). [4] INTERNATIONAL ATOMIC ENERGY AGENCY, RCA/ IAEA third External Dosimetry Intercomparisons in East Asia Region, Proc. of the European workshop on Individual Monitoring of Ionising Radiation (IM2005) Vienna April 2005, Radiat. Prot. Dosim., IAEA, Vienna (in press). [5] INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Occupational Exposure Due to External Sources of Radiation, IAEA Safety Standards Series No. RS-G-3.1, IAEA, Vienna (1999). [6] FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR ORGANIZATION, OECD NUCLEAR ENERGY AGENCY, PAN AMERICAN HEALTH ORGANIZATION, WORLD HEALTH ORGANIZATION, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, IAEA, Vienna (1996). 29

38

39 I-1. General Information Name of the laboratory Head of the laboratory Contact person for the intercomparison Address Fax: Tel: Type of dosimeter provided ANNEX I. NOMINATION FORM AND QUESTIONNAIRE FOR PARTICIPATING LABORATORIES Number of workers monitored in the following practices? Name of Practice Number of workers being monitored Radiodiagnostic departments in hospitals Radiotherapeutic departments in hospitals: beam therapy brachytherapy Nuclear medicine departments in hospitals: diagnostic techniques therapeutic techniques Industrial radiography (non-destructive testing) Irradiation facilities (industrial and research) Industrial gauging applications: thickness (mass) measurement level detection moisture determination well-logging Analytical techniques (industrial and research): diffraction techniques fluoroscopy techniques 31

40 neutron activation techniques Research activities (industrial and academic laboratories): sealed sources and generators unsealed radioactive materials Minerals extraction and processing companies Research reactors and nuclear research facilities Power reactors Fuel cycle facilities including enrichment, fuel fabrication and reprocessing facilities Isotope production operations and source manufacturing Uranium mines Significant exposure to natural radionuclides I-2. Dosimetric quantities and calibration of dosimeters Is the individual exposure to external radiation measured as personal dose equivalent Hp(10)? If the response to the above point is No, please explain: Yes/No Quantity to be measured the total personal dose equivalent the personal dose equivalent of the neutron and the photon component (measuring both parts separately) the personal dose equivalent of the neutron component only (insensitive to photons) Energy range and energy dependence Yes/No Yes/No Yes/No The photon dosimeter is suited for the photon energy range from (please enter values and units) to Enter comments here if necessary: Dosimeter used Please specify the type of personal dosimeter used (e.g. TLD, film): Please specify the name of manufacturer, model of the TLD reader, and the type of TLD card or type of film used. Could you provide a photo for the dosimeter. Calibration Are calibration dosimeters exposed on an appropriate phantom? If No, why not? Yes/No 32