Speaker
Description
The Customs Service performs X-ray security screening to prevent illicit articles from entering the country. The primary contraband products that are illegally distributed include unspecified forms of narcotics, explosives, and seeds. The challenge in detecting these contraband items using a conventional transmission X-ray inspection system alone stems from their tendency to be concealed as thin layers in luggage, in addition to their low atomic number and density. However, backscatter X-ray imaging, based on Compton scattering, has been shown to provide superior image contrast compared with transmission imaging for these materials [1]. Because of these advantages, backscatter imaging has been widely adopted for detecting contraband in baggage, vehicles, and port containers. In our previous study, the Geant4 (Geometry and Tracking4) simulation toolkit was employed to optimize the design of a backscatter X-ray scanner and to obtain the backscatter images for performance estimation [2]. In the present study, the reliability of the Geant4 simulation model for the backscatter X-ray security scanner was experimentally validated. This validation was conducted by employing two gamma sources (i.e., Am-241 and Co-57) and a radiation generator operating at 100 kV and 3 mA. For the gamma sources, the energy spectrum of a large-area monolithic PVT detector was measured at 30, 40, and 50 cm from the detector. To obtain the backscatter X-ray images, the object was scanned by the collimated pencil-beam (i.e., flying spot) while moving at 5 cm/s on a conveyor belt. In the simulation, the X-ray source term was obtained by monoenergetic-electron-beam bombardment onto the target. Also, the scanning pencil-beam and moving object were simulated by using G4Messenger. To validate the simulation model, a comparison was made between the simulated and measured image profiles, as well as the energy spectra of the PVT detector. The percent differences between the simulated and measured energy spectra and the image profiles were all found to be within 5%. Consequently, it was determined that the simulation model for the backscatter X-ray scanner can be relied upon.
[1] S Huang et al., Opt. Express, 27 (2019), 337-349
[2] G An et al., JINST, 18 (2023), C01004
The authors acknowledge funding from the National Research Foundation of Korea (NRF) funded by the Korea Customs Service and Ministry of Science and ICT (NRF-2021M3I1A1097913).
| Workshop topics | Applications |
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