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.

The Contributions to Registration Efficiency of The Fast Neutron Reactions on The Nuclei of The Heavy Oxide Scintillators

“…This paper presents the experimental results of measurements of contributions of multiple gamma quanta generated both in inelastic scattering and in resonance and radiation capture of neutrons by oxide scintillators. In addition, it was experimentally confirmed in our work [3] that the growth of useful statistics of events due to cascade gamma quanta, which are caused by incident neutrons, ultimately leads to an increase in the sensitivity of the neutron detector.…”

“…At the first stages of research [8], the contribution of high-energy gamma quanta (E ~ 0.5-3 MeV) from the inelastic scattering reaction (n, nʹγ) arising during the discharge of excited solid-state scintillator nuclei was carried out by smallsized oxide scintillators, V ~ 1 cm 3 . At the same time, the efficiency of the registration of fast neutrons, measured by a spectrometric path with an integration time of τ = 30 us and a registration threshold of ~ 20 keV, was ε ~ 0.4 -0.5 counts/neutron.…”

“…In the future, in order to increase the counting efficiency of fast neutron registration, in our works [2,3,26] it was proposed to register multiple (cascade) gamma quanta generated between the highly excited transitions of final nuclei in the reactions of the interaction of neutrons with nuclei. For this purpose, it was proposed to register, in addition to the products of the inelastic scattering reaction, also the products of the resonance scattering and capture reactions.…”

Counting Efficiency and Neutron/Gamma Ratio for KDP: Tl+ and UPS-923A Scintillators in a Single Photone Detection Mode

“…The lifetimes of isomeric states excited in reactions with fast neutrons are in the range [3] from a few nanoseconds to hundreds of microseconds. Therefore, the measuring path includes a fast preamplifier [4] with a gain of 70 dB and an intrinsic rise time of ~ 1.5 ns. The preamplifier is used to register signals in the photon-counting mode.…”

“…In view of the increased radiation resistance (~ 10 10 neutron/cm 2 ) of the obtained new crystals, an urgent task is to study the interaction of neutron radiation with the substance of KDP: TL + . As shown in our previous works [1][2][3][4][5][6][7][8][9][10], neutron radiation can be detected using scintillation crystals of potassium dihydrogen phosphate KH 2 PO 4 (KDP), which are doped with thallium ions Tl + [5]. This paper presents the experimental results of a study of the efficiency of fast neutron detection in water-soluble crystals in the photon-counting mode and pulse timefiltering mode.…”