The Threshold of Detection of Fission Materials by ZnWO4 and Bi4Ge3O12 Scintillation Detectors

Abstract

In the present work we found the maximum discovery distance for ²³⁹Pu-Be source using the detectors based on ZWO (ZnWO₄) and BGO (Bi₄Ge₃O₁₂) oxide scintillators. Detection distance was defined by using the radiation monitoring system ”PORTAL”. This research gives us data for estimation of the contribution of low-energy cascade gamma quanta CGQ. The CGQ emitted by excited scintillator nuclei defined the effective discovery distance of the fast neutrons source. The maximum detection distance was obtained with PMT in a single-photon counting mode. The maximum discovery distance for a BGO scintillator of size Ø40×40 mm – 38 cm, ZWO scintillator of size Ø52×40 mm – 54 cm, with reliability about 0.001. The results of the experiment on the ZWO scintillator can be explained by the registration of additional gamma quanta from the inelastic scattering reaction and the CGQ arising from resonant neutron capture region. This two mechanisms further lead to increase the sensitivity of the detector and increase the detection distance of the monitoring system. The key features of the monitoring system are: ZWO oxide scintillator, wide band measuring path, utilize PMT in single photon mode. The obtained detection distance was about 1.4 times higher in comparison with the spectrometric recording mode and 1.9 times higher in values of efficiency. Our results demonstrate the advantages of the ZWO scintillator compared to the BGO and demonstrate the possibility of using the resonant capture mechanism by ZWO detector nuclei to increase the fast neutrons sensitivity. The resonance capture mechanism increase sensitivity and maximum detection distance of the monitoring system. The low-energy gamma-quanta, which discharge of compound nuclei, are substantially suppressed in comparison with the classic spectrometric recording mode.