Chemical Composition Analysis for X-Ray Transport Container Scans
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hemical Composition Analysis for X-Ray Transport Container Scans A. Zelenayaa, *, M. Zelenyia, b, **, A. A. Turingea, and V. G. Nedorezova, *** a
INR RAS, Moscow, 117312 Russia Dolgoprudny, Moscow Region, 141701 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected]
bMIPT,
Received March 4, 2019; revised March 20, 2019; accepted March 29, 2019
Abstract—It is important for national security to control the movement of dangerous or strategically cargo such as explosives, radioactive materials, rare and precious metals. This control can be provided by scanning transport containers by gamma rays. In this report the existing technique for scanning (dual energy method) is considered and the alternative method based on measuring the energy distribution of gamma rays is proposed. For estimation perspectives of the proposing method, the corresponding simulation was conducted by using the GEANT4 toolkit. The example of the algorithm of reconstruction the chemical composition of the scanned object is also considered. In addition the experiment for estimation energy resolution of the detector based on a scintillation crystal BGO and SiPM was carried out. DOI: 10.1134/S1063779619050253
INTRODUCTION The use of high-energy gamma radiation in applied tomography is already quite widespread. In this paper, we consider the possibilities of improving the existing technique both by modernizing the equipment and by developing mathematical algorithms that more fully utilize the information contained in the measured values. Firstly, we consider the existing dual energy method and determine possible directions for creating a more accurate method. Further, the paper describes several simulations and numerical experiments with a discussion of the results. The paper also presents the results of measurements of the characteristics of a BGO scintillation crystal, which can be as a basis for modernized equipment. DUAL ENERGY METHOD Consider how the flux of gamma rays decreases. Transmittance is described by the following equation: E0
S(E , E ) exp(−μ(E , Z )t)dE ) 0
T (E0, t, Z ) =
0
E0
,
(1)
S(E , E )dE 0
0
material, E0 —up-limit energy of bremsstrahlung, E — energy of gamma ray, Z —charge of nuclei. We assume that bremsstrahlung is used as a source of gamma rays, with a spectrum, for example, as in Fig. 1b and with the maximum energy depending on the energy of the electron beam. Our transmittance also depends on the mean material attenuation coefficient. Figure 1a shows the dependence of the attenuation coefficient on energy for different materials. We can distinguish three areas: the initial one in which the photoelectric effect dominates and only materials with a large nuclear charge stand out; the average in which Compton scattering dominates and materials are not distinguishable, and the area where the main influence is produced by the production of electron-positron pairs, and the materials are quite well distinguishable [1–3]. The last area can be used for the dual
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