(Thursday, 7/16/2020) 11:30 AM - 12:30 PM [Eastern Time (GMT-4)]
Room: Track 3
Purpose: The ability to identify radioisotopes is the key element of radiation protection, nuclear medicine and disaster emergency situations. We exploited interfacial radiation transport effects in multilayered High-Energy Current (HEC) detector structure to distinguish gamma ray emitting radio-isotopes in a wide range of keV-MeV energies. To achieve this, optimization of materials and detector geometry was necessary.
Methods: We performed ~1000 radiation transport simulations studying numerous multilayer geometries with N-basic elements composed of 3-electrodes: N x (Al-aerogel-Ta-aerogel-Al). The electrodes number and thicknesses were optimized depending on the incident x-ray spectra and its ability to penetrate different layers and/or interact with them producing fast electrons. In the balanced design, the electrodes have increasing thicknesses as a function of electrode depth from 0.5µm-Ta and 10µm-Al at the entrance up to 10mm-Ta and 2.5mm-Al at the exit. Each aerogel layer was 50µm-thick. Fast electron currents forming RIID-signals were acquired from all Ta electrodes, providing characteristic multi-channel signal profiles traceable to unique radionuclide spectra. Subsequently, we developed two radioisotope identification algorithms suitable for unknown unshielded and shielded sources.
Results: Characteristic detector response profiles for monoenergetic beams (10keV-6MeV) and radioisotopes (I-125, Pd-103, Ir-192, U-235, Pu-239, Cs-137, Co-60) were determined and used to develop two inverse radioisotope identification algorithms. Using these, we identified the unshielded and shielded sources. We also quantified the minimum, mean and maximum effective energies and estimated the amount of background Compton photons in the isotope spectra.
Conclusion: We devised a balanced architecture of a multilayer thin-film RIID measuring fast electron current profiles to identify radioisotopes in a wide range of energies (20keV-1.35MeV). The device is intrinsically rugged, self-powered and can withstand very high dose rates allowing deployment in difficult conditions or following radiation incidents. The algorithms we developed for radioisotope identification are robust and constitute an important component of RIID in practical applications.
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