Comparison of prompt and delayed photofission neutron detection ttechniques using different types of radiation detectors

For several years, detection of various threats on country borders plays a significant role in the frame of Homeland Security applications. One of this threat is the illicit trafficking of nuclear materials (especially including Special Nuclear Material — SNM — ²³⁵U, ²³³U or ²³⁹Pu), which can be potentially used for production of nuclear weapon as well as radiological dispersal device (RDD) — known also as a “dirty bomb”. In order to detect the potentially hidden nuclear material, systems using linear accelerators and a group of detectors are developed by several scientific groups around the world. Besides solutions focusing on detection of delayed γ-rays or neutrons, also the systems dedicated for prompt neutron detection were proposed. One of the possible prompt neutron detection technique is known as Threshold Activation Detection (TAD). This technique relies on activation of ¹⁹F nuclei in the scintillator medium by fast neutrons and registration of high-energy β particles and γ-rays from the decay of reaction products (for example, ¹⁹F(n,α)¹⁶N or ¹⁹F(n,p)¹⁹O). Recent studies in the frame of the European Horizon 2020 C-BORD project showed that, despite the low ¹⁹F(n,α)¹⁶N or ¹⁹F(n,p)¹⁹ O reaction cross-section, the method could be a good solution for detection of shielded nuclear material. A benchmark of the TAD technique based on fluorine detectors with reference method focused on delayed neutron detection with ³He detectors will be presented in this paper. These experimental results were obtained using 9 MeV Varian Linatron M9 linear accelerator (LINAC).