RU2781041C1 - Scintillation composition for neutron detection - Google Patents

Abstract

FIELD: ionizing radiation registration.

SUBSTANCE: invention relates to the field of registration of ionizing radiation. The scintillation composition for detecting neutrons contains a scintillator, a neutron absorber and a binder. The addition of ⁶Li atoms to the composition of the binder makes it possible to increase the efficiency of neutron absorption, reduce energy losses, and reduce the mean free path of helium and tritium nuclei between ⁶Li nuclei and scintillator grains in the composition. In this case, the ratio of the number of gadolinium atoms Gd and ⁶Li can vary widely, allowing neutrons to be detected mainly by the reaction of radiative capture (n, γ), or by the reaction of absorption of neutrons by ⁶Li nuclei, accompanied by the emission of helium and tritium nuclei.

EFFECT: improvement of spatial resolution and productivity of measurements during neutron registration.

1 cl, 5 tbl, 2 ex, 2 dwg

Description

The invention relates to devices for detecting ionizing radiation, namely neutrons by the method of scintillation neutron imaging, radiography and tomography, using compositions consisting of inorganic scintillation materials and neutron absorbing materials.

State of the art

A known neutron imaging method using gadolinium-containing scintillators, in which the neutron absorber is initially part of the scintillation material, for example, scintillation ceramics Gd ₂ O ₂ S (GOS, Gadox), activated with Tb ³⁺ ions, or Tb ³⁺ and Ce ^{3 +} , or Tb ³⁺ and Eu ³⁺ , co-activated with F ^- ions, or particles of LiF, ⁶ LiF, etc. (E.I. Gorokhova, V.A. Demidenko, S.V. Mikhrin, P.A. Rodnyi, and C.W. E. van Eijk. Luminescence and Scintillation Properties of Gd ₂ O ₂ S:Tb, Ce Ceramics. IEEE transactions on nuclear science , vol. 52, no. 6, December 2005), (Tobias Neuwirth, Bernhard Walfort, Simon Sebold and Michael Schulz. Light Yield Response of Neutron Scintillation Screens to Sudden Flux Changes. J. Imaging 2020, 6(12), 134; https://doi.org/10.3390/jimaging6120134).

The thickness of GOS screens varies in the range of 10-50 microns. The experimentally observed spatial resolution for a Gd ₂ O ₂ S:Tb screen thickness of 10 µm is 36 µm (Xingfen Jiang, Qinglei Xiu, Jianrong Zhou et al. Study on the neutron imaging detector with high spatial resolution at China spallation neutron source. Nuclear Engineering and Technology 53 (2021) 1942-1946). At the same time, the authors note that the low scintillation yield (light yield) of the Gd ₂ O ₂ S:Tb screen of 217 ± 2 photons per neutron, at least 100 times worse than that of ⁶ LiF/ZnS, requires a huge increase in the neutron flux to reduce the exposure to almost acceptable level.

The absorption cross section for thermal neutrons by gadolinium is 49,000 Barn for a natural isotope mixture and 254,000 Barn for the ¹⁵⁷ Gd isotope present in the natural mixture in an amount of 15.6%. For a unique screen made of enriched gadolinium ¹⁵⁷ Gd ₂ O ₂ S:Tb, with a screen thickness of 3.5 µm, the spatial resolution was 5.4 µm (Pavel Trtik, Eberhard H. Lehmann. Progress in High-resolution Neutron Imaging at the Paul Scherrer Institut The Neutron Microscope Project Journal of Physics: Conference Series 746 (2016)012004).

A common disadvantage of all gadolinium-containing scintillation screens is the fact that the absorption of a thermal neutron in gadolinium is accompanied by the emission of low-energy X-rays and internal conversion electrons with an energy of tens of keV. The emitted γ-quanta have an energy spectrum up to ~8 MeV, but at energies above 100 keV they have an insignificant absorption efficiency in a thin screen, which leads to a decrease in its counting efficiency (probability of detecting a neutron). According to (A. Fedorov, V. Gurinovich, V. Guzov et al. Sensitivity of GAGG based scintillation neutron detector with SiPM readout. Nuclear Engineering and Technology. V.52, N10 (2020) 2306-2312), lowering the upper threshold of electron detection and γ-quanta in the gadolinium-containing neutron detector GAGG (Gd ₃ Al ₂ Ga ₃ O ₁₂ ) from 8 MeV to 105 keV reduces the counting efficiency of the neutron detector from 92% to about 44%.

According to (Anderson, I.S.; McGreevy, R.L.; Hassina, Z.B. Neutron Imaging and Applications: A Reference for the Imaging Community; Technical report; Springer: Berlin/Heidelberg, Germany, 2009; ISBN 978-0-387-78692-6), The registration of neutrons in the GOS screens is carried out mainly due to the absorption of conversion electrons.

For thin GOS screens with a thickness of 10 µm or less, one can only count on effective registration of the conversion electron ¹⁵⁸ Gd* with an energy of 29 keV, which has a yield per neutron of 0.0982 according to (P. Kandlakunta, LR Cao, P. Mulligan. Measurement of internal conversion electrons from Gd neutron capture. Nucl. Instrum. Meth. in Phys. Res. A 705(2013)36-41), thus the counting efficiency of such a neutron detector cannot exceed 10%. For thicker, up to 50 μm, GOS screens capable of detecting ¹⁵⁸ Gd* conversion electrons with energies up to about 78 keV, the counting efficiency will increase with a simultaneous deterioration in energy resolution, but will not exceed 35–40% according to the same authors.

Low scintillation yield per absorbed neutron and low counting efficiency are significant disadvantages of GOS screens, which ultimately lead to a significant increase in exposure and decrease in measurement performance based on the use of GOS.

In addition, according to (E.I. Gorokhova, V.A. Demidenko, S.V. Mikhrin, R.A. Rodnyi, and C.W. E. van Eijk. Luminescence and Scintillation Properties of Gd ₂ O ₂ S:Tb,Ce Ceramics, IEEE transactions on nuclear science, vol. at relatively high neutron fluxes. In this case, the limitation of measurement performance occurs due to a decrease in the loading capacity of the detector, due to the duration of the kinetics of the scintillation pulse, since the registration rate R is proportional to

,

,

where

n - average rate of arrival of events,

t ₁ - the duration of the scintillation pulse,

t ₂ - the duration of its leading edge

(E. Cabin, Nuclear Electronics for Users, http://nuclphys.sinp.msu.ru/electronics/deadtime.htm).

In scintillators based on inorganic oxygen compounds activated by rare-earth ions, the duration of the scintillation pulse is three times the value of the scintillation decay kinetics constant, and the leading edge does not exceed its single value.

A known method of neutron imaging using screens containing a scintillator based on zinc Zn: ZnS-Ag, ZnS-Cu, Al, etc., a neutron absorber based on lithium fluoride ⁶ LiF and a binder (Anderson, IS; McGreevy, RL; Hassina, ZB Neutron Imaging and Applications: A Reference for the Imaging Community, Technical report, Springer: Berlin/Heidelberg, Germany, 2009, ISBN 978-0-387-78692-6), (EHLehmann, G.Frei, G.Kühne , P Boillat The micro-setup for neutron imaging: A major step forward to improve the spatial resolution Nucl Instrum Meth in Phys Res A 576, 389 (2007) 389-396).

The advantage of ZnS-Ag/ ^6LiF scintillation material (VB Mikhailik et al., Investigation of luminescence and scintillation properties of ZnS-Ag/6LiF scintillator in the 7-295 K temperature range, J. Luminescence 134 (2013) 63-66) is faster kinetics, scintillations, the main component of the decay kinetics is 4.5 μs, which is five hundred times shorter than that of the terbium ion-activated GOS scintillation material.

The advantage of scintillation screens based on lithium ZnS-Ag/ ⁶ LiF is that the absorption of a thermal neutron in ⁶ Li is accompanied by the emission of high-energy particles, the helium nucleus (α-particle) and the tritium nucleus (triton), having an energy of 2.055 MeV and 2.727 MeV, respectively. Such particle energies provide high brightness of scintillation flashes in ZnS, up to 160,000 photons per neutron, and at the same time mean relatively short particle ranges in the scintillation layer - a few microns for α-particles and tens of microns for tritons.

According to (Anderson, IS; McGreevy, RL; Hassina, ZB Neutron Imaging and Applications: A Reference for the Imaging Community; Technical report; Springer: Berlin/Heidelberg, Germany, 2009; ISBN 978-0-387-78692-6), The thicknesses of the ZnS-Ag/ ⁶ LiF screens used in neutron imaging vary within 250-100 µm, less often reach 50 µm, which is explained by a much smaller thermal neutron absorption cross section of ⁶ Li, 940 Barn than that of Gd, and a significant loss of efficiency thinning screen.

In (EH Lehmann, G. Frei, G. Kuhne, P. Boillat. The micro-setup for neutron imaging: A major step forward to improve the spatial resolution. Nucl. Instrum. Meth. in Phys. Res. A 576, 389 (2007)) at the neutron spallation source SINQ, Switzerland, with a ZnS-Ag/ ⁶ LiF screen thickness of 50 µm with a cooled CCD chamber, a spatial resolution close to the theoretical limit of about 50 µm, or 20 line pairs, was obtained /mm at 10% modulation transfer function (MTF) contrast. The expected result of reducing the thickness of the screen was a decrease in counting efficiency and measurement productivity.

Typically, the weight proportions of the components included in the ZnS-Ag/ ⁶ LiF screen are distributed as follows: ZnS-Ag/ ⁶ LiF:binder = 1:2-4:0.15-0.6 (Tobias Neuwirth, Bernhard Walfort, Simon Sebold and Michael Schulz, Light Yield Response of Neutron Scintillation Screens to Sudden Flux Changes, J. Imaging 2020, 6(12), 134; https://doi.org/10.3390/jimaging6120134), (Y. Yehuda-Zada, K. Pritchard , JB Ziegler et al. Optimization of ⁶ LiF:ZnS(Ag) scintillator light yield using GEANT4. Nucl. Instrum. Meth. in Phys. Res. A 892 (2018) 59-69), (Gnezdilov, GL Dedenko, RF Ibragimov et al., Optimization of the neutron detector design based on the ⁶ LiF/ZnS(Ag) scintillation screens for the GAMMA-400 space observatory, Conference of Fundamental Research and Particle Physics, 18-20 February 2015, Moscow, Russian Federation, Physics Procedia 74 (2015) 199 - 205). Variations of ZnS activators have a greater effect on the kinetics of scintillations and their spectrum, and to a lesser extent on the yield of scintillations, which is usually determined by various manufacturers and users in the range of 100,000-160,000 photons per neutron. The effect of component proportions on the characteristics of the ZnS-Ag/ ⁶ LiF screen, revealed by the authors (Y. Yehuda-Zada, K. Pritchard, JB Ziegler et al. Optimization of ⁶ LiF: ZnS(Ag) scintillator light yield using GEANT4. Nucl. Instrum. Meth. in Phys. Res. A 892 (2018) 59-69) during GEANT4 (S. Agostinelli et al. Geant4 - a simulation toolkit. Nucl. Instrum. Meth. in Phys. Res. A. 506 (2003)250 -303) simulations are shown in Table 1:

An increase in the concentration of ZnS grains impairs the transmission of scintillation light to the photodetector, since ZnS grains are practically opaque to the light of their own scintillations. ZnS at the scintillation wavelength has an exceptionally high refractive index of n=2.36, which far exceeds that of any substance that could be used as a binder. For this reason, the scintillation light propagating in the screen will inevitably enter the ZnS grains and be absorbed there. Ideally, the refractive index of the binder should be higher than that of ZnS to eliminate the influence of its opacity.

An increase in the concentration of ⁶ LiF grains reduces the scintillation yield, since first of all, it introduces additional losses of the kinetic energy of α-particles and tritons in ⁶ LiF grains on the way to the scintillator grains (self-absorption) and, moreover, worsens the transmission of scintillation light to the photodetector, because ⁶ LiF grains, although transparent to the light of ZnS scintillations, will be the centers of light scattering of these scintillations in the case when the refractive index of the binder is higher than that for ⁶ LiF, n=1.39 according to (Refractive index database. https://refractiveindex.info /?shelf=main&book=LiF&page=Li). Any scattering leads to an increase in the optical path of light in the screen and, as a result, to inevitable absorption in ZnS grains.

Scattering can be reduced by increasing the grain size of ⁶ LiF to 2-3 microns, or several wavelengths of ZnS scintillations. But this inevitably increases the energy loss of α-particles and tritons due to self-absorption. 1 and 2 show the results of a GEANT4 simulation of the energy loss in ⁶ LiF and a typical epoxy binder. It can be seen that the total energy loss of α-particles and tritons with a path length of 5 μm ⁶ LiF reaches 45% of the initial one, and for α-particles it is 91%. When passing 5 µm in the binder, the energy loss is 1.6 times lower.

In figure 1 and figure 2 the length of the run is the path of the particles in the substance, or the total length of their trajectory. The path lengths of α-particles and tritons in ⁶ LiF obtained by modeling from the point of entry into the substance to the stopping point are shown in Table 2.

Another possible way is to reduce the grain size of ⁶ LiF to submicron, on the order of small fractions of the ZnS scintillation wavelength in order to go beyond the limits of the ratio of the size of the scattering object to the wavelength characteristic of Mie scattering, towards Rayleigh scattering. However, uniform and homogeneous placement of any submicron particles in the screen without aggregation is difficult from a technological point of view, as evidenced by a comparison of simulation results and experimental data (Y. Yehuda-Zada, K. Pritchard, JB Ziegler et al. Optimization of ⁶ LiF:ZnS( Ag) scintillator light yield using GEANT4 Nucl Instrum Meth in Phys Res A 892 (2018)59-69).

A known method for creating scintillation screens based on ZnS/H ₃ BO ₃ compositions (Guo L., Liu Z., Luo Z. Preparation method of thermal neutron scintillation screen, CN 104538078 A. Apr. 22. 2015), where the phosphor is based on sulfide zinc is mixed with boric acid, heated until a homogeneous melt is obtained, which is then poured into a special recess of an aluminum plate that serves as a substrate.

A known method for creating a boron-containing composition (Jansma B.J., J. L. Water based dispersions of boron or boron compounds for use in coating boron lined neutron detectors, US 2011116589 A1. May 19. 2011), in which aqueous suspensions of elemental boron-10 were used, which were applied to a substrate as a sublayer for the conversion of neutrons into detectable gamma quanta with an energy of 0.48 MeV or alpha particles with an energy of 2.79 MeV.

A common disadvantage of the described boron-containing compositions is that the reaction of the boron-10 isotope with a neutron in 93% of cases proceeds through the formation of low-energy gamma rays with an energy of 0.48 MeV, which have an extremely low absorption efficiency in a thin scintillation screen.

These disadvantages can be eliminated by using a lithium absorber, when all of it, or at least part of it, is distributed in the binder at the atomic level, i.e. forms a single optically transparent chemical compound with the binder, in which there are no scattering centers, leading to an increase in the optical path length of scintillation photons in the composition. In this case, all the above simulation results and the corresponding conclusions regarding the role of the absorber and binder in the composition of the neutron scintillation screen are valid not only for a screen based on ZnS, which is practically opaque to its own radiation, but also based on other scintillators, the refractive index of which is higher than the refractive index of the binder. .

Disclosure of the essence of the invention

The technical problem to be solved by the claimed invention is to achieve a better spatial resolution in the implementation of the possibility of using a smaller amount of neutron absorber ( ⁶ LiF).

The technical result of the claimed invention is to improve the spatial resolution and performance of measurements during neutron detection in tasks of scintillation neutron imaging.

The technical result of the claimed invention is achieved by the fact that a scintillation composition for detecting neutrons containing a scintillator, a neutron absorber and a binder is proposed, while gadolinium-containing compounds of the type Gd3-xYxAl5-yGayO12 are used as a scintillator, which can have both a high content of gadolinium atoms, as in the compound Gd3Al2Ga3O12, and reduced by their full or partial replacement with Y atoms or lanthanides, as in Gd3-xYxAl2Ga3O12, or Y3Al5O12 and / or in which there is a changed ratio of Al and Ga atoms, as in Gd3-xYxAl5-yGayO12, or compounds from the series: Gd2O2S, GdCl3, GdBr3, Gd2SiO5, Gd2Si2O7, Gd3Al2Ga3O12 in the form of grains of a single-crystal or polycrystalline material containing cerium atoms as an activator, which are introduced into the composition of the material, replacing one or more elements in an amount of 0.001 to 2 at.%, or containing as an activator terbium and / or europium atoms, which are introduced into the m material, replacing one or more elements in an amount from 0.1 to 20 at. %, lithium fluoride 6L1F is used as a neutron absorber, lithium silicate with the formula 6Li2O*nSiO2, or lithium polyacrylate with the formula (C3H3O26Li)n is used as a binder, and the ratio of the volumes of 6LiF and 6Li2O*nSiO2, or (C3H3O26Li)n in the composition is ranging from 99:1 to 1:99.

The combination of the above essential features leads to the fact that:

The addition of ⁶ Li atoms to the composition of the binder makes it possible to increase the efficiency of neutron absorption, reduce energy losses, and reduce the mean free path of helium and tritium nuclei between ⁶ Li nuclei and scintillator grains in the composition. In this case, the ratio of the number of gadolinium atoms Gd and ⁶ Li can vary over a wide range, allowing neutrons to be detected mainly by the reaction of radiative capture (n, γ), or by the reaction of absorption of neutrons by ⁶ Li nuclei, accompanied by the emission of helium and tritium nuclei, and thus achieve the required combination of sensitivity and spatial resolution;

It is possible to use a smaller amount of the neutron absorber ( ⁶ LiF), or in some cases completely abandon it, thereby facilitating the receipt of more light from the scintillation layer, as well as achieving better spatial resolution.

Brief description of the drawings

In FIG. Figure 1 shows the energy losses of α-particles and tritons as a function of their path length in ⁶ LiF.

In FIG. 2 shows the energy loss of α-particles and tritons depending on the length of their path in a binder based on epoxy resins.

Implementation and examples of the invention

To achieve this technical result, a scintillation composition is proposed for detecting neutrons by the reactions of radiative capture (n, γ) by the nuclei of a natural mixture of gadolinium, accompanied by the emission of γ-quanta, X-rays and internal conversion electrons, as well as by the reaction of absorption of neutrons by ⁶ Li nuclei, accompanied by the emission helium and tritium nuclei, consisting of scintillator particles containing gadolinium Gd atoms, including ⁶ Li atoms of neutron absorber particles and an optically transparent binder, also containing ⁶ Li atoms. In this case, all components of the composition contain atoms with nuclei that absorb neutrons with a capture cross section of at least 1 Barn in the range of kinetic energies up to 10 MeV. As a scintillator, gadolinium-containing compounds with a natural mixture of isotopes of Gd atoms, or enriched in the required isotope, are used. At the same time, gadolinium-containing compounds can have both a high content of gadolinium atoms, as in the Gd ₃ Al ₂ Ga ₃ O ₁₂ compound, and a reduced content through their complete or partial replacement by Y atoms or lanthanides, as in Gd _3-x Y _x Al ₂ Ga ₃ O ₁₂ , or Y ₃ Al ₅ O ₁₂ and/or in which an altered ratio of Al and Ga atoms is present, as in Gd _3-x Y _x Al _5-y Ga _y O ₁₂ . Partial or complete substitution of gadolinium for yttrium or other lanthanides makes it possible to achieve the required combination of neutron absorption efficiency and scintillation light yield. Thus, the Gd ₃ Al ₂ Ga ₃ O ₁₂ : Ce compound has a light yield of 41000 photons per 1 MeV of absorbed energy, the Gd _1.2 Y _1.785 Al ₂ Ga _2.97 O ₁₂ : Ce compound has up to 60000 photons/MeV, and Y ₃ Al ₅ O ₁₂ : Ce 11000 photon/MeV, but in the case of Y ₃ Al ₅ O ₁₂ :Ce, the conversion of neutrons into detectable particles (helium and tritium nuclei) occurs solely due to the presence ^{of 6} LiF in the composition. Also, as a scintillator, you can use gadolinium-containing compounds from the series: Gd ₂ O ₂ S, GdCl ₃ , GdBr ₃ , Gd ₂ SiO ₅ , Gd ₂ Si ₂ O ₇ , Gd ₃ Al ₂ Ga ₃ O ₁₂ , Gd _3-x Y _x Al _5-y Ga _y O ₁₂ in the form of grains of a single-crystal or polycrystalline material containing cerium atoms as an activator, which are introduced into the composition, replacing one or more elements in an amount of from 0.001 to 2 at. %. Or compounds from the series: Gd ₂ O ₂ S, GdCl ₃ , GdBr ₃ , Gd ₂ SiO ₅ , Gd ₂ Si ₂ O ₇ , Gd ₃ Al ₂ Ga ₃ O ₁₂ , Gd _3-x Y _x Al _5-y Ga _y O ₁₂ in the form of grains of single-crystal or polycrystalline material, containing terbium and/or europium atoms as an activator, which are introduced into the composition, replacing one or more elements in an amount of from 0.1 to 20 at. %. The concentration of the activator should lie within the specified limits, since at a lower concentration of the activator the light output of the scintillator will be too low for practical applications, and at high concentrations, the scintillation is quenched by the activator, as a result of which the light output is significantly reduced.

The refractive index of gadolinium-containing compounds is significantly lower than that of the traditionally used ZnS-based scintillator and does not exceed n=1.9. Compounds containing atoms of the isotope ⁶ Li are used as a binder.

On the basis of natural lithium isotopic composition, and then enriched up to 90% in the ⁶ Li isotope, optically transparent binders were selected, Table 3.

The expected volume ratio ^{of 6} LiF and ⁶ Li ₂ O*nSiO ₂ , as well as ⁶ LiF and (C ₃ H ₃ O ₂ Li) _n in the composition can be in the range from 99:1 to 1:99, which is due to practical considerations for obtaining a uniform scintillation layer of a certain thickness, as well as to obtain the desired ratio of lithium and scintillator atoms in the composition.

Practical implementation includes the following operations:

A) preparation of the scintillator;

B) preparation of the absorber;

B) preparing a binder;

D) preparation of the composition by homogeneous mixing of the components and application of the resulting composition on a reflective substrate.

Example 1

Fabrication of a sample of a scintillation screen based on a composition with a scintillator - ground ceramics of the composition Gd _1.2 Y _1.785 Ce _0.015 Al ₂ Ga _2.97 O ₁₂ , absorber grains ⁶ LiF and binder ⁶ LiPA.

Operation A) The precursor of gadolinium, yttrium, aluminum, cerium-activated gallium garnet, obtained by co-precipitation of cations in the form of carbonates, was calcined at a temperature of at least 850°C, crushed and compacted by uniaxial pressing at a pressure of 60 MPa. The compacts were sintered in air at a temperature of at least 1500°C. Thus obtained ceramics were crushed, scattered through a 350 mesh sieve and a fraction with d _0.5 =15-20 μm was separated.

Operation B) The neutron absorber was prepared from commercially available lithium compounds enriched in the ⁶ Li isotope by converting them into a highly soluble mineral acid salt, which was reacted with an ammonium fluoride solution taken with an excess of 10% of the stoichiometry. The precipitated ⁶ LiF was washed from the mother liquor, dried, dispersed through a 350 mesh sieve, and a fraction with d _0.5 =2-3 μm was separated.

Operation C) Lithium-6 polyacrylate was obtained from commercially available lithium compounds enriched in the isotope ⁶ Li and polyacrylic acid as follows: polyacrylic acid heated in a water bath to a temperature of 50-60 ° C (commercial 35-40% solution) was mixed with water in a mass ratio of 1/0.8-0.9 and then with vigorous stirring, a weighed portion of the lithium-6 compound, taken in a stoichiometric ratio in terms of the monomer, was slowly added. Air and other gas impurities were removed from the resulting solution of lithium-6 polyacrylate by degassing in a vacuum desiccator at a residual pressure of not more than 10 mm Hg.

Operation D) To obtain a composition with a volume ratio of binder/absorber/scintillator equal to 40/30/30, a suspension was prepared, which was homogenized and degassed in a laboratory mixer equipped with a vacuum system. The mass ratios of the components were 0.335/0.203/0.462, respectively. Dispersants and rheological additives were added to the slurry to achieve optimum slurry viscosity and a dense, even layer.

The resulting suspension was applied to the substrate using one of the known methods for applying suspensions to the surface. The substrate was placed between the guides and the required volume of suspension was applied to the edge, which was then distributed over the entire area with a polished spiral rod. The composite layer was left to dry in air under conditions that prevented the ingress of dust onto the surface of the sample.

Example 2

Fabrication of a sample of a scintillation screen based on a composition with a scintillator - ground ceramics of the composition Gd _1.2 Y _1.65 Tb _0.15 Al ₂ Ga ₃ O ₁₂ , absorber grains ⁶ LiF and binder ⁶ LiPS.

Operation A) The precursor of gadolinium, yttrium, aluminum, gallium garnet, activated by terbium, obtained by co-precipitation of cations in the form of carbonates, was calcined at a temperature of at least 850°C, crushed and compacted by uniaxial pressing at a pressure of 60 MPa. The compacts were sintered in air at a temperature of at least 1500°C. Thus obtained ceramics were crushed, scattered through a 350 mesh sieve and a fraction with d _0.5 =15-20 μm was separated.

Operation B) The neutron absorber was prepared from commercially available lithium compounds enriched in the 6Li isotope by ^converting them into a highly soluble mineral acid salt, which was reacted with an ammonium fluoride solution taken with an excess of 10% of the stoichiometry. The precipitated ⁶ LiF was washed from the mother liquor, dried, dispersed through a 350 mesh sieve, and a fraction with d _0.5 =2-3 μm was separated.

Operation B) Lithium-containing silicate binder composition ⁶ Li ₂ O⋅nSiO ₂ , where n=1-6 was obtained by hydrolysis of tetraethoxysilane with a given amount of 6-lithium hydroxide solution.

Operation D) To obtain a composite with a volume ratio of binder/absorber/scintillator equal to 4/73/23, a suspension was prepared, which was homogenized and degassed in a laboratory mixer equipped with a vacuum system. The mass ratios of the components are 0.434/0.331/0.235, respectively.

The resulting suspension was applied to the substrate using one of the known methods for applying suspensions to the surface. The substrate was placed between the guides and the required volume of suspension was applied to the edge, which was then distributed over the entire area with a polished spiral rod. The composite layer was left to dry in air under conditions that prevented the ingress of dust onto the surface of the sample. The characteristics of the samples obtained are shown in Table 4.

The measurements of the fabricated samples were carried out using monochromatic neutrons with a wavelength of 2.4 Å (14 meV). GOS(Tb) (Gd ₂ O ₂ S:Tb) and ZnS(Ag)/ ⁶ LiF screens 46 µm and 100 µm thick, respectively, were used as reference samples.

The spatial resolution was measured by placing a slit cadmium mask in front of the composite and an image was obtained, which was processed. Along the length of the segment corresponding to 100 pixels of the recording system, which crossed the mask boundary, the light intensity was determined for each pixel. The intensity was determined in units of the gray scale. The first derivative was calculated from the values of shades of gray and a graph of the dependence of the first derivative on the coordinate was plotted. The half-width at half-height (FWHM) of the obtained peak in pixels was calculated and the resulting value was multiplied by the value of the size of one pixel of the optical system, which was 65 microns.

The results of measurements of the spatial resolution of the samples and the parameters of their scintillation kinetics are presented in Table 5.

The spatial resolution obtained for samples 1 and 2 exceeds that for ZnS(Ag)/ ⁶ LiF and approaches GOS(Tb). A positive effect was achieved due to the contribution of the reaction (n, γ) to the spatial resolution of samples No. 1 and No. 2, and their yield of scintillations per absorbed neutron significantly, more than 10 times, exceeded that for GOS(Tb) due to the contribution of the reaction to nuclei ⁶ Li.

The duration of the scintillation pulse in the developed sample No. 1 is 25,000 times shorter than that of the GOS(Tb) reference sample, and 55 times shorter than the ZnS(Ag)/ ⁶ LiF reference sample. The recording speed, and therefore the measurement performance, is increased accordingly.

Claims (1)

A scintillator composition for detecting neutrons containing a scintillator, a neutron absorber and a binder, characterized in that gadolinium-containing compounds of the form Gd _3-x Y _x Al _5-y Ga _y O ₁₂ are used as a scintillator, which can have both a high content of gadolinium atoms , both in the Gd ₃ Al ₂ Ga ₃ O ₁₂ compound, and reduced by their complete or partial replacement with Y atoms or lanthanides, as in Gd _3-x Y _x Al ₂ Ga ₃ O ₁₂ or Y ₃ Al ₅ O _12, and /or in which there is a changed ratio of Al and Ga atoms, as in Gd _3-x Y _x Al _5-y Ga _y O ₁₂ , or compounds from the series: Gd ₂ O ₂ S, GdCl ₃ , GdBr ₃ , Gd ₂ SiO ₅ , Gd ₂ Si ₂ O ₇ , Gd ₃ Al ₂ Ga ₃ O ₁₂ in the form of grains of a single-crystal or polycrystalline material containing cerium atoms as an activator, which are introduced into the composition of the material, replacing one or more elements in an amount from 0.001 to 2 at. %, or containing terbium and / or europium atoms as an activator, which are introduced into the rest of the material, replacing one or more elements in an amount from 0.1 to 20 at.%, lithium fluoride ⁶ LiF is used as a neutron absorber, lithium silicate with the formula ⁶ Li ₂ O*nSiO ₂ is used as a binder, or lithium polyacrylate with the formula ( C ₃ H ₃ O ₂ ⁶ Li) _n , and the ratio of the volumes ^{of 6} LiF and ⁶ Li ₂ O*nSiO ₂ , or (C ₃ H ₃ O ₂ ⁶ Li) _n in the composition is in the range from 99:1 to 1:99 .

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