Gennadiy M. Onyshchenko

High efficiency fast neutron detectors based on inorganic scintillators

The possibility was studied of using highly efficient heavy inorganic oxide solid-state scintillation detectors for the detection of mixed gamma-neutron radiation. In the detection of gamma-neutron radiation, the gamma detection efficiency for such detectors reaches 70-80%, with neutron detection efficiency not less than 40%. Detection efficiencies were measured for the heavy oxide scintillator crystals CWO (CdWO₄), ZWO (ZnWO₄), BGO (Bi₄Ge₃O₁₂), GSO (Gd₂SiO₅), YSO:Ce (Y₂SiO₅:Ce) and LuAG:Ce (Lu₃Al₅O₁₂:Ce). For comparison purposes, the scintillators NaI:Tl, LiI:Eu, ZnSe(Te), CsI(Tl) were also considered. The dependencies of detection efficiency on Zeff, thickness and area of the detector were obtained. To eliminate the effects of accompanying gamma-radiation in the detection of neutrons, suppression of gamma-background was studied using lead protection of 2-40 mm thickness as well as a protection screen consisting of a cylindrical ring of BGO with an internal diameter of 40 mm and an external diameter 60 mm surrounding a cylindrical CWO scintillator detector of dimension 40×40 mm. Suppression of the gamma background by factors of 2-10 was achieved with passive protection. With the BGO screen in an active mode, gamma background suppression reached 10³. Also, an original “windows” method [1] of data analysis was proposed for mathematical processing of gamma background, with appropriate software, allowing us to reach neutron/gamma ratios from 10⁵ to 10⁷.

Detection of gamma-neutron radiation by novel solid-state scintillation detectors

In this work, we present results of our experimental and theoretical studies on the detection efficiency of fast neutrons from 239Pu-Be and 252Cf sources by the heavy oxide scintillators BGO, GSO, CWO and ZWO, as well as ZnSe(Te, O). We have investigated the efficiency of registration of the combined γ and neutron radiation from Pu-Be and Cf-252 neutron sources and have explored the possibility of suppressing the γ-radiation by several methods - passive protection by lead shielding, active defense by detector design and the use of special software for gamma discrimination. The last method is the most promising, but it requires more detailed development. In addition, we provide examples of practical applications of these results, as well as the results of our search for new ways to develop large-sized detectors of lower cost by creating a new multilayer structure from composite (flexible) scintillator panels alternated with transparent plastic scintillator layers that serve as light guides.

The higher efficiency fast neutrons detectors based on the oxide scintillators

Results are presented of studies on detection efficiency of fast neutrons by oxide scintillators CWO, BGO, GSO, ZnWO, LiI(Eu). It is shown that the most probable mechanism of high efficiency detection of fast neutrons is reaction of inelastic scattering on heavy nuclei of the scintillator material (n, n’γ). High efficiency of fast neutron detection has allowed creation of high efficiency small-sized detectors of gamma-neutron radiation on the basis of “scintillator-PMT” system for stationary and pedestrian inspection systems, as well as high efficiency small-sized neutron detector for portable systems

Fast neutron detectors based on solid-state single crystalline and multilayer composite scintillators

We report on the development and analysis of two types of fast neutron and neutron-gamma detection media: (1) large volume inorganic oxide crystalline scintillators; and (2) large-area multilayer composite structures consisting of dispersed granules of small-crystalline scintillators contained in a transparent plastic matrix. The first type is based on solid-state single crystal CWO, BGO and ZWO scintillators of large size (diameter 30-50 mm, length up to 100 mm). For these large crystals, we have experimentally confirmed previous results demonstrating very high efficiency for fast neutron detection (up to 50%), which were obtained earlier on small-sized samples of smaller (about 10-12 cm3) volume. Such larger-size scintillators are needed in order to increase detector sensitivity for the detection of very small quantities of neutron-emitting radioactive materials. In our subsequent search for new efficient and cost effective solid-state neutron detectors, we have developed and studied the second type of detection media: large area multi-layer composite detectors (named ZEBRA). We measured the sensitivity of a 40×100×100 mm multilayer ZEBRA detector (with a total thickness 40 mm, and a scintillator cross sectional layer of area 100 cm2) comprised of dispersed GSO(Ce) and found it to be comparable to the normal sensitivity of a 3He-detector with an area of 4000 cm2. The efficiency of ZEBRA detectors is not lower than 50%, i.e., approximately at the same level of detection achieved by single crystal scintillators. The cost of such composite detectors is projected to be substantially lower than that of neutron/gamma detectors based on conventional single crystals.

A new multi-layer scintillation detector for detection of neutron-gamma radiation

We present the results of our experimental and theoretical studies of fast neutron detection efficiencies of a newly-developed multi-layer scintillation detector comprised of a series of alternating layers of a composite inorganic scintillator material and an optically transparent plastic scintillator material (brand ZEBRA). We investigated the response of this type of detector to neutrons from 239Pu-Be and 252Cf sources. We evaluated the sensitivity of such ZEBRA detectors as a function of different thicknesses of the alternating layers of composite scintillator and light guides to optimize the performance of these structures. We compared the detection efficiency of these detectors with detectors based on the single crystals ZnSe, ZWO and GSO. We also analyzed the detection sensitivity of these crystal scintillation detectors as a function of thickness and cross-sectional area of the detection material. Finally, we created software that permits the achievement of a high level (up to 104) suppression of gamma-radiation from both accompanying and other external gamma-radiation.

New neutron detectors based on inorganic scintillators using inelastic scattering

Detection efficiency of fast and thermal neutrons was studied for detectors based on scintillators LiI(Eu), CWO, BGO, GSO, ZnWO4, CsI(Tl), ZnSe(Te), used in systems for detection of fissionable substances. Results are presented of our studies aimed at practical application of an efficient method for detection of fast and thermal neutrons, which uses the process of inelastic scattering on atom nuclei present in inorganic scintillators. The most evident practical application field for this method is inspection systems for prevention of illegal transportation of radioactive substances.

Use of GSO scintillators in x-range radiometers

In radiometers for X-range, the use of scintillators based on gadolinium orthosilicate (GSO) has many advantages over alkali halide scintillators, e.g., NaI(Tl). The shape of spectra obtained with GSO and cadmiug tangstate (CWO) scintillators has certain features that substantially increase the sensitivity of radiometers which use the windows method algorithm and are designed for simultaneous detection of low-energy gamma-radiation of 241Am (59.6 keV) and 137Cs (~33 keV). These features of oxide scintillators have allowed a substantial increase in sensitivity of the radiometer RK-AG-02M, which is designed for detection of 241Am on the background of 137Cs. The results obtained in this work show that the use of GSO and (in several cases) CWO scintillators in the instruments involving X-ray range of radiation (e.g., meters of thickness, radiometers) is very promising field of their application. We consider also the effects of different factors related to thermal treatment upon dopant-activated complex oxide crystal to improve its optic-luminescent, scintillation and other functional characteristics. In the selective radiometer RK-AG-02M are using a scintillation block based on GSO scintillator. To increase the measurement accuracy in the bulk density range of 0.6-2.5 g/cm3 correcting function has been obtained for the radiometer sensitivity.