APPLICATIONS OF MUON TOMOGRAPHY FOR THE DETECTION OF HIDDEN NUCLEAR SUBSTANCES IN CONTAINERS

Transcription

1 APPLICATIONS OF MUON TOMOGRAPHY FOR THE DETECTION OF HIDDEN NUCLEAR SUBSTANCES IN CONTAINERS IPRD10, 7 June 2010, Siena, Italy M. Benettoni, P. Checchia, E. Conti, F. Gonella, G. Nebbia INFN Padova, Italy G. Mariotti, S. Pesente, S. Vanini, G. Viesti, G. Zumerle Univ. & INFN Padova, Italy G. Bonomi, A. Zenoni, Univ. & INFN Brescia, Italy P. Calvini, S. Squarcia Univ. & INFN Genova, Italy

2 MUON TOMOGRAPHY: Source Primary cosmic particles (~p) interacting with high atmosphere produce particles cascades. At see level the charged particle flux is cosmic rays / (minute * m 2 ) and most of them are muons (µ),( with mean energy of 3 4 GeV VERY PENETRATING RADIATION 40 Flux µ/(m 2 s sr GeV) p (GeV/c) 20% 2

3 MUON TOMOGRAPHY: Measurement Principle Multiple Coulomb Scattering Muons traveling through a material are deviated from their original trajectory. The deviation angle (projected on a plane) has a Gaussian distribution, with mean value 0 and RMS depending on: the inverse of the muon momentum (1/p), the material thickness (x), the radiation length (X 0 ), which depends on 1/Z: σ = MeV x [ log( x / X )] MeV c x β pc X p X X 0 = / 2 ( g cm ) ρ A Z( Z + 1) log(287 / Z ) 3

4 MUON TOMOGRAPHY: Multiple Scattering Different materials different scattering angles measure scattering angles to determine presence, position, shape and type of materials Possibility to discriminate fissile material or shielding materials als from low and medium Z materials Useful for inspections of cargo containers & trucks without a radioactive source Approximate multiple scattering for muons passing through 10 cm of various materials Material Water Concrete Iron Lead Uranium Radiation Length (cm) RMS scattering (mrad) expected for muons with momentum: 0.3 GeV/c GeV/c GeV/c The information contained in the scattering angle is stochastic => need statistics The scattering angle depends on the momentum of the muon, that is a priori unknown 4

5 EXPERIMENTAL SETUP At the INFN National Laboratory of Legnaro (Padova, Italy) an apparatus for the study of muon radiography has been assembled using two spare Muon Chambers Detectors, produced for CMS (CERN experiment at LHC) Two Drift Chambers 2.5x3.0 m 2 Gap between chambers: 160 cm (vol m 3 ) 2 extra SLs to measure p; Fe p-filterp Trigger: upper chamber (events pointing from upper to lower chamber) Acquisition rate: 350 Hz 5

6 CMS MUON CHAMBERS DETECTORS Drift chambers (built for CMS experiment at CERN): position resolution 200 µm angular resolution (for p = GeV/c) 1 mrad in PHI view (2 SuperLayers, with high lever arm) 10 mrad in THETA view (1 SL, no high lever arm) 90% cosmic ray flux has p 10 GeV/c so resolution is worse because of multiple scattering on the materials of the chamber itself (40mm of Al). muon PHI view THETA view Drift cell 6

7 DATA ANALYSIS Pattern recognition software identifies hits of the same track (selects the best straight line fits) and solves left right ambiguity inherent to any drift chamber; Track reconstruction algorithm: track trajectory is computed with a fit algorithm, position and slope of the track is calculated; Event selection: Single track in both views; 6-8 hits in phi SL, 4 hits in theta SL; => Good tracks after selections: 65% for each chamber Image reconstruction: Rigorous data treatment requires a maximum likelihood approach together with iterative techniques similar to those applied in the advanced processing of medical imaging data (PET, SPECT). The results presented in this contribution are obtained using a 3D projector-backprojector pair (proback) where only angular deviations are modeled. a 3D tomographic reconstruction incorporating the angular deviation and the effects of lateral shift, called x displacement. (Ref. L.J. Schultz, IEEE TRANSACTIONS ON IMAGE PROCESSING, VOL. 16, NO. 8, AUGUST 2007) 7

8 IMAGING CAPABILITY OF THE SYSTEM INFN made of Pb blocks 2 Pb bricks (left) + 2 Fe bricks (right) at different height Top view, slice at z=80cm Iron table frame T acq ~ 8 min with optimized detectors Results published in NIM A, 604 (2009) Position of the blocks reconstructed correctly - Reconstructed scattering density for Pb larger than for Fe. - Poor spatial resolution along the vertical direction (only the scattering angle ( Φ Φ) used!) 8

9 MATERIAL RECOGNITION Discrimination among different materials: The scattering density reconstructed on the basis of the scattering angle standard deviation should be proportional to the inverse of the material radiation length. Al Cu W (4,8,12 cm) Pb (5,10 cm) Fe 10 cm Brass 10 cm 10 cm Non-linearity in reconstructed scattering density! Hypothesis: each sample produces a different low momentum cut in the momentum distribution of the muon events used for reconstruction 9

10 MOMENTUM EFFECT Without momentum evaluation the basic relation is 2 C x ( Φ) 2 p X Traversing the sample material, the low momentum component of the muon spectrum is absorbed, to an extent depending on the sample nature and thickness. This effect can be responsible for non-linearity 0 simulation 10 cm cubes Momentum evaluation seems to be mandatory to be sensitive in dense environments. Improved algorithms: sensitivity improves if <1/p 2 > substituted by a proper (numerical) integration over the momentum spectrum. Momentum filter: large (Fe) absorbers below the inspection volume allow to tag low p tracks. Analysis of the muons, observed in the upper chamber but not in the lower one (absorbed or with a large scattering angle). 10

11 POSSIBLE APPLICATIONS DETECTION OF ORPHAN SOURCES SCRAP MATERIAL INTO CONTAINERS OF IMAGING OF LARGE ENEGINEERING CONSTRUCTIONS [1] NUCLEAR FUEL DRUMS MONITORING [2] MONITOR OF THE STABILITY OF LARGE MECHANICAL STRUCTURES [3] ANALYSIS OF RADIOACTIVE WASTE CONTAINERS INSPECTION OF CARGO CONTAINERS FOR THE DETECTION OF NUCLEAR AND RADIOACTIVE MATERIAL 1. P.M. Jenneson, Large vessel imaging using cosmic-ray muons NIM A 525 (2004) J. Gustafsson, Tomography of canisters for spent nuclear fuel using cosmic-ray muons, Uppsala University Neutron Physics Report ISSN Diploma thesis 3. I. Bodini, G. Bonomi et al. Cosmic ray detection based measurement systems: a preliminary study, Meas. Sci. Technol. 18 (2007)

12 DETECTION OF ORPHAN SOURCES INTO CONTAINERS OF SCRAP MATERIAL Scrap metal is used in a quite large way by the steel industry, being the recycling of the iron suggested by economical as well as by environmental motivations. The week point of the recycling chain is the possibility that the scrap metal cargo is contaminated by other materials affecting the quality of the final steel product. Moreover, a strong concern is related to the possibility that orphan radioactive sources might be placed inside a cargo. This has created in fact large problems when the orphan source was melted in the steel production plants, creating important contaminations that generated large financial losses. 12

13 THE AVF BELTRAME ACCIDENT As an example of a contamination event in steel industry, on Jan 13 th 2004 a melt of a 1.35 GBq (35 mci) 137 Cs source occurred at the Beltrame production plant in Vicenza (Italy). This contamination caused economical losses (13 MEuro) and a contamination of the area around the production plant. Another source of the same type was detected about one week earlier by the radiation portals. But this happened since in this case the shutter of the source shielding cask was open. 13

14 RECONSTRUCTION IN DENSE ENVIRONMENT Two 15 cm thick, 80 x 100 cm 2 area, iron blocks are placed between the two chambers. An iron structure is placed between the 2 chambers. It is possible to add different samples, heavy blocks or containers in the volume between the chambers. Four reference lead bricks are placed close to the corners, on top of chamber 2. The typical scrap metal density is about 0.8 g/cm 3, almost an order of magnitude lower than bulk iron. With such a density, a 2.5 m thickness (the typical cargo dimension) of scrap metal corresponds to about 26 cm of bulk iron. 14

15 RECONSTRUCTION USING DISPLACEMENT ( x)( Scattering angle ( Φ) ( Φ Scattering angle ( Φ) ( Φ ) + displacement ( x)( Detector Φ x Detector Spatial resolution along the vertical direction is improved! The upper iron plane is not well reconstructed. Work is in progress! 15

16 Pb BLOCK PLACED BETWEEN TWO Fe PLANES 3D muon tomography images, scattering angle ( Φ) ( Φ ) + displacement ( x)( ) used Geometry of the experimental test: two 15 cm thick iron planes and a lead block, 20x25 cm 2, 15 cm thick. The sample is well recognizable with the expected density. 16

17 LEAD VS IRON CASTLES UP Lead Down Iron Density >0,5 Density >2,5 Density >4 17

18 LEAD VS IRON CASTLES LEAD OBJECT IRON OBJECT 18

19 WITH AND WITHOUT MOMENTUM INFORMATION 3D muon tomography images, scattering angle ( Φ) ( Φ ) + displacement ( x)( 3D muon tomography images, scattering angle ( Φ) ( Φ ) + displacement ( x)( ) + 1/p 2 Work in progress 19

20 Goals: MUSTEEL Design a detection portal for the steel industry based on the muon technology to complement the existing radiation devices. Study the feasibility of the technique (some min/container: data acquisition + reconstruction) Design the portal (detectors and geometry) Build a small prototype (hardware and software). Estimate the portal costs Partners: INFN, Universities of Padova and Brescia, Tecnogamma SpA, SRB Costruzioni, AVF Beltrame. Status: Project was submitted to the Coal&Steel Research Fund of EU, it was approved. T 0 : July 1 st,

21 CONCLUSIONS A large-scale prototype of muon tomography with large inspected volume and excellent tracking capability has been built and operated; Muon tomography of a large volume 3x2.5x1.6 ~ 12 m 3 has been performed successfully. Inspected volume has been visualized in 3D with a real tomographic image. It is possible to determine different shapes and positions of materials. Results show that it is possible to extract information about the average composition of the objects in the volume under inspection and discriminate among different materials. Problems in the discrimination between Pb and much dense materials as W due to the absorption of the low energy muon spectrum that biases the reconstruction of the scattering density. Studies using muon momentum are in progress. Improvements of image reconstruction software are in progress (p and Θ information added). Detection test of a lead castle embedded in iron have been successfully performed. 21

22 THANK YOU! 22

23 ECONOMICAL AND ENVIRONMENTAL IMPORTANCE OF THE METAL RECYCLING Over 400 million tonnes of metal is recycled each year worldwide. Virtually all metals can be recycled into high quality new metal, the process being different for different metals, but generally producing items of equivalent quality. Metals recycling protects the environment and saves energy. Using secondary raw materials means less use of natural resources which would otherwise be needed to make new metal compounds such as iron ore in steelmaking. There are also considerable savings in energy, and reduced CO 2 emissions, in production methods using recycled materials. EU figures indicate that using recycled raw materials, including metals, cuts CO 2 emissions by some 200 million tonnes every year. Using recycled steel to make new steel enables reductions such as: 86% in air pollution, 40% in water use, 76% in water pollution respect to the production using new metal compounds 23

24 ORPHAN SOURCES 24

25 NOTABLE ORPHAN SOURCE ACCIDENTS WORLDWIDE 25

26 ACCIDENT ECONOMICAL COSTS 26

27 DETECTING SOURCES WITH RADIATION PORTALS Portals: plastic scintillator large area detectors Scrap Metal Truck: 9 m L, 2.4 m W, 2.5 m H, placed at 80 cm from the detector Scrap Metal Density: 0.8 g/cm 3 Naked Source: no additional Pb Shielded source: 15 cm dia Pb transportation cask 27

28 CURRENTLY AVAILABLE TECHNOLOGY: X-RAY SCANNERS The typical scrap metal density is about 0.8 g/cm 3, almost an order of magnitude lower than bulk iron. With such a density, a 2.5 m thickness (the typical cargo dimension) of scrap metal corresponds to about 26 cm of bulk iron, requiring a very energetic (few MV) X-ray source to be inspected. Costs, licensing problems and operational complexity strongly suggest the search for alternative inspection systems to complement the existing radiation portals. Need of 4-5 MV system to detect Pb cask in a scrap metal truck. Problems with false positive due to thick chunks of steel in the scrap 28

29 HOW MUCH TIME IS NEEDED FOR INSPECTION? Monte Carlo test case: - 110x110x110 cm 3 cube filled with scrap metal (Fe with density 0.8 g/cm 3 ) - 30x30x30 cm 3 of lead placed in the middle Discrimination between Fe and Pb. Monte Carlo (a.u.) 29

30 HOW MUCH TIME IS NEEDED FOR INSPECTION? 10 and 5 minutes irradiation Monte Carlo (a.u.) (a.u.) (a.u.) 30

31 HOW MUCH TIME IS NEEDED FOR INSPECTION? 8 minutes irradiation Experiment 31

32 WORK IN PROGRESS vuoto Fe 10 cm Pb 10 cm Pb 15 cm 32

33 Reconstruction using scattering angle ( Φ( Φ) ) + displacement ( x)( Normalized Scattering Density (a.u.) W 4 cm, Pb 5 cm W 8 cm W 12 cm /X 0 (cm 1 ) 33