V. Ryzhikov

Thermal neutron detectors based on complex oxide crystals

Abstract The ways of improvement of spectrometric quality of CWO and GSO crystals have been investigated with the aim of their application in thermal neutron detectors based on radiation capture reactions. The efficiency of the neutron detection by these crystals was measured, and the obtained data were compared with the results for 6LiI(Tl) crystals. It is shown that the use of complex oxide crystals and neutron-absorption filters for spectrometry of thermal and resonance neutrons could be a promising method in combination with computer data processing. Numerical calculations are reported for spectra of gamma-quanta due to radiation capture of the neutrons. To compensate for the gamma-background lines, we used a crystal pair of heavy complex oxides with different sensitivity to neutrons.

The role of oxygen in formation of radiative recombination centers in ZnSe1−xTex crystals

The present study was aimed at revealing the influence of oxygen on formation of alloy ZnSe–ZnTe as well as on development of luminescence centers under thermal treatment of scintillators based on isovalently doped ZnSe crystals. The presence of oxygen in ZnSe(Te) crystals as ZnO phase has been shown to hinder formation of (V′ZnTexSe)′ type luminescence centers responsible for luminescence band peaked at 635–640 nm, which is the principal emission band of this scintillator. In ZnSe(Te) crystals doped by mechanically stimulated ion implantation with active forms of oxygen (O′, Ox, O′2, etc.), luminescence quenching effects are not observed. However, the luminescence band in these crystals is blueshifted towards 600–610 nm. Strong luminescence band peaked at λmax=590–610 nm is observed in Te-free ZnSe crystals doped with oxygen in active forms. The experimental results are interpreted by formation of centers (Zni⋅Oxi)⋅ or (Zni⋅OxSe)⋅. Having larger charge carrier capture cross-section than (Zn⋅iV′ZnTexSe)x, the oxygen-containing centers determine kinetics of luminescence in ZnSe1−xTex crystals (x<0.001) treated by active forms of oxygen during mechanical activation of the initial raw material for crystal growth.

Improvement of optical and luminescent characteristics and radiation hardness of PbWO4 crystals by doping with Y, Sb, and Mo impurities

Abstract The influence of combined doping with Sb, Y and Mo, Y impurities on the optical transmittance, radiation hardness, intensity and spectra of X-ray luminescence of PbWO 4 scintillation crystals has been investigated. Doping the PbWO 4 crystals with Sb (100 ppm) and Mo (500 ppm) shifts the X-ray luminescence spectra from 430–450 to 520 nm region and increases its intensity and decay time. The highest intensity is observed in crystals simultaneously doped with all three dopants (Mo, Sb, Y). The results can be explained by formation of microinclusions of tungstenite phase in doped PWO crystals.

Influence of doping on radiation stability of scintillators based on lead tungstate and cadmium tungstate single crystals

This paper reports the results of measurements of optical transmittance, thermoluminescence, and radiation hardness of lead and cadmium tungstate (PWO and CWO, respectively) doped crystals. It was found that three-valent impurities increase the optical transmittance of PWO crystals but decrease the transparency of CWO crystals. The radiation hardness for both types of crystals sufficiently increases after doping. Different kinds of defects that provide the observed effects are discussed.

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 thermal and resonance neutrons using oxide scintillators

Results are presented for pulse amplitude spectra of crystals based on complex oxides irradiated in mixed fields of neutron and gamma-radiation. These crystals-CdWO/sub 4/ (CWO), Gd/sub 2/Si/sub 2/O/sub 5/(Ce) (GSO(Ce)) and NaBi(WO/sub 4/)/sub 2/-include elements with large radiation capture section of thermal and resonance neutrons. It has been shown that it is possible in principle to separately detect products of nuclear reactions of radiation capture of neutrons on Cd, W, Gd and Na nuclei. This is realized by the appropriate choice of energy windows during detection of nuclear reaction products and the accompanying gamma-radiation using scintillators with different decay times and different interaction cross-sections, as well as with the help of screens selectively absorbing neutrons or gamma-quanta.

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 neutron detectors based on oxide scintillators for control of fissionable radioactive substances

A large-area X-ray CMOS image sensor (LXCIS) is widely used in mammography, non-destructive inspection, and animal CT. For LXCIS, in spite of weakness such as low spatial and energy resolution, a Indirect method using scintillator like CsI(Tl) or Gd2O2S is still well-used because of low cost and easy manufacture. A photo-diode for X-ray imaging has large area about 50 ~ 200 um as compared with vision image sensors. That is because X-ray has feature of straight and very small light emission of a scintillator. Moreover, notwithstanding several structure like columnar, the scintillator still emit a diffusible light. This diffusible light from scintillator can make spatial crosstalk in X-ray photodiode array because of a large incidence angle. Moreover, comparing with vision image sensors, X-ray sensor doesn’t have micro lens for gathering the photons to photo-diode. In this study, we simulated the affection of spatial crosstalk in X-ray sensor by comparing optical sensor. Additionally, the chip, which was fabricated in 0.18 um 1P5M process by Hynix in Korea, was tested to know the effect of spatial crosstalk by changing design parameters. From these works, we found out that spatial crosstalk is affected by pixel pitch, incident angle of photons, and micro lens on each pixels.

Application prospects of cadmium-containing crystals based on tungstates and double tungstates

Tungstate and double tungstate crystals of high scintillation efficiency and detectors based on them are applied widely in the medical imaging and radiation monitoring because of their high sensitivity to the ionizing radiation, small radiation length, high radiation hardness, low afterglow level. In this work a possibility to broaden the application field of CWO crystals have been investigated by improvement of their spectrometric quality and decreasing of their afterglow level. CWO crystals with improved characteristics have been obtained (resolution for 137 Cs o8%, afterglow o0.02% after 20 ms). A possibility is considered to use these crystals for spectrometry of thermal and resonance neutrons, which is possible due to the presence of nuclei with large cross-section for these neutrons in the crystal lattice. Compounds of a new type based on Cd, La-containing double tungstates doped with rare earth elements have been synthesized, and their luminescent characteristics have been studied. Calculation and measurement results are presented for these crystals under thermal and resonance neutron activation. The results obtained show that such crystals are very promising for dosimetry and spectrometry of neutrons at thermal energies. r 2002 Elsevier Science B.V. All rights reserved.

Combined detectors based on ZnSe(Te), CsI(Tl) and Si-PIN-PD for separate detection of alpha, beta and gamma radiation

Combined detectors (CD) comprising ZnSe(Te), CsI(Tl), and Si-PIN-PD can be used for detection of charged particles and gamma quanta. The detection is based on selective sensitivity and the different decay times of these scintillators for these kinds of radiations. In this paper, we outline possibilities and limitations of CD in which signals are read by an 18/spl times/18 mm/sup 2/ Hamamatsu S3204 Si-PIN-PD placed on the back side of CsI(Tl) crystal. A specially designed charge-sensitive preamplifier connected to a PD has equivalent noise level of 700 electrons during shaping time of 5 /spl mu/s. The CD-Si-PIN-PD system is compatible with modern computers.