RU2627573C1 - Scintillation material for detecting ionising radiation (versions) - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: scintillation material for detecting ionising radiation is a crystalline solid solution with the general empirical formula Li(Y_1-x Lu_x)F₄ with x=0.01-0.8 formed in the binary system LiYF₄ - LiLuF₄. Also, the scintillation material for detecting ionising radiation is a crystalline solid solution with the general empirical formula Ba(Y_1-x Yb_x)₂F₈ with x=0.01-0.9 formed in the binary system BaY₂F₈ - BaYb₂F₈.

EFFECT: production of scintillation materials, including large ones, with the possibility of directional sensitivity control of these materials to ionizing radiation with maximum sensitivity to γradiation-quantities.

11 cl, 1 dwg

Description

The invention relates to materials used in scintillation technology, primarily in high-speed, effective scintillation detectors, designed to detect various types of ionizing radiation: neutron, x-ray and γ-radiation, and can be used in medicine, industry, space technology, scientific research.

The requirements for scintillators (SCs) contain at least a dozen items, the main of which are: speed, that is, short flash times (τ); high conversion efficiency (light output, L); high radiation resistance; low afterglow and good mechanical properties; The spectral composition of the radiation is also important for combination with the photodetector used. High speed and high conversion efficiency of scintillators are essential for creating highly sensitive detectors with a high event counting rate.

A number of patents are known in which various scintillation materials are proposed.

RF patent No. 2056638, publ. 03/20/1996, SCINTILLATION MATERIAL FOR REGISTRATION OF IONIZING HIGH ENERGY RADIATIONS (OPTIONS)

The inventive proposed high-density (ρ = 6.12 g / cm ³ ) and radiation-resistant (10 ⁹ rad) materials that can be used as scintillators in the registration systems of ionizing radiation, in particular in electromagnetic calorimeters. Single crystal ρ materials are a solid solution based on CdF ₂ with the addition of fluoride RF ₃ , where R is cerium, lanthanum, or a mixture thereof, corresponding to the empirical formulas Cd _1-x Ce _x F _{2 + x} , Cd _0,99 La _0,01 F _2.01 , Cd _0.98 La _0.01 Ce _{0.01 0.01} F _2.01 . Another material is a solid solution based on single-crystal cerium fluoride with the addition of cadmium fluoride corresponding to the empirical formula Ce _0.995 Cd _0.005 F _2.995 . Single crystals were grown by the Bridgman-Stockbarger method in graphite crucibles in a fluorinating atmosphere. The invention is aimed at increasing the radiation resistance of the synthesized crystal due to the different ratio of 2 components in it.

Patent No. 2436123 dated 12/10/2011 proposes a scintillation material, which is a crystalline base of barium fluoride and contains a dopant in the form of scandium fluoride, characterized in that it is presented in the form of a BaF ₂ -ScF ₃ single crystal with a dopant concentration of ScF ₃ - 0 05-2.0 mol. % When using the claimed material in the scintillator device as a working medium, the following values of the main characteristics of the scintillator device operation are achieved: the effect of suppressing the long-term component of the glow at least 1.7 times with an increase of at least 3.6 times the intensity of the ultrafast component; ultrashort (subnanosecond) flash time is 0.4-0.8 ns. The invention is aimed at reducing the time of emission of the main crystal of barium fluoride due to the addition of scandium fluoride.

Of particular interest are single-crystal scintillators based on inorganic fluorine-containing compounds. Compared to oxygen-containing materials, fluorides are characterized by an advantageous possibility for the detection of high-energy particles, since in this case, a greater number of electron-hole pairs are generated in fluoride crystals, which gives a greater light output. Higher ionization energies than oxides give a greater choice of crystalline matrices, for example, for a luminescent ion widely used in scintillators, such as Ce ³⁺ , which has a tendency to reduction (Ce ³⁺ -> Ce ²⁺ ). Thus, LaF ₃ and YF ₃ crystals doped with Ce ³⁺ ions have effective luminescence, while in La ₂ O ₃ and Y ₂ O _{3 the} cerium luminescence is quenched due to the electronic transition from the excited 5d state to the conduction band. As for comparison with other halides, fluorides have high chemical resistance. In addition, they are additionally characterized by:

1) lack of toxicity (compared with thallium activated sodium or cesium iodates);

2) sufficient hardness (compared with chlorides, bromides, iodates);

3) the absence of hygroscopicity (compared with the compounds of claim 2);

4) high resistance to chemically aggressive environments, including hydrofluoric acid vapor.

However, the main requirements when choosing a SC for detecting ionizing γ-radiation, in addition to the main ones listed above, are the need to have materials with maximum values of the effective atomic number (Z) and matrix density (ρ). The ability of the crystalline matrix to retain x-ray or γ-rays, i.e., scintillator sensitivity to detection of the latter. In a first approximation [A. Yosikawa, T. Suyama, K. Fukuda et al. “Scintillator for neutron detection and neutron detector”, RF Patent No. 2494416] this ability is a function of ~ ρ Z ⁴ (where Z = (Σ w _i z _i ⁴ ) ^1/4 , here w _i and z _i - mean mass fraction and atomic number of the i-th element among the elements making up the matrix). Fluorides of "heavy" metals (Y, La, Ce, Gd, Yb, Lu, Pb, Zr, Hf) having large densities (for example, ρ (YF ₃ ) = 5.06 g / cm ³ , ρ (LuF ₃ ) = 8.3 g / cm ³ ) and effective atomic numbers Z> 50, they are sensitive to x-ray and gamma radiation and they are conventionally considered to be “heavy” scintillators, and single crystals consisting of fluorides of “light” metals (for example, ρ (LiF) = 2.64 g / cm ³ , ρ (CaF ₂ ) = 3.18 g / cm ³ ) with Z <50, are sensitive to neutron radiation and they are considered “light” scintillators.

The closest analogues, in coincidence of the chemical formulas of crystalline compounds, but essentially different from the characteristic features and results of the present invention, are the results published in RF patent No. 2367731, which describes a method for producing activated LiY _1-x Lu _x F ₄ solid solutions crystals ions Ce ³⁺ and Nd ³⁺ for alternative use as laser media to increase the concentration of cerium and neodymium ions due to disordering (loosening) crystal matrix structure, and in pa ente RF №2369670, which also exclusively as a laser substance-UV treated crystals BaY ₂ F _8: Ce ³⁺ ions soaktivirovannye Yb ³⁺ and Lu ^3+, which allow to increase the efficiency of laser operation on 5d-4f transition of cerium ions in this material. The crystals were obtained by the Bridgman-Stockbarger method.

The objective of the invention is to obtain scintillation materials, including bulky, with the possibility of directional control of the sensitivity of these materials to ionizing radiation with maximum sensitivity to radiation of γ-quanta.

To solve this problem, a scintillation material is proposed for detecting ionizing radiation, which is a crystalline solid solution with the general empirical formula Li (Y _1-x Lu _x ) F ₄ at x = 0.01-0.8, which is formed in the binary system LiYF ₄ - LiLuF ₄ .

Wherein:

- for registration of neutron radiation x = 0,01,

- for registration of x-ray and γ-radiation x = 0.5-0.7,

- the material is activated by Ce ³⁺ or Pr ³⁺ ions in an amount of 0.5-1.5 mol.%,

- the material obtained by the method of horizontal directional crystallization,

- the material is a single crystal in the form of a plate with dimensions of at least 50 × 80 × 20 mm.

Also proposed is a scintillation material for detecting ionizing radiation, which is a crystalline solid solution with the general empirical formula Ba (Y _1-x Yb _x ) ₂ F ₈ at x = 0.01-0.9 formed in the binary system BaY ₂ F ₈ - BaYb ₂ F ₈ .

Wherein:

- for registration of x-ray and γ-radiation x = 0.5-0.7.

- the material is activated by Ce ³⁺ or Pr ³⁺ ions in an amount of 0.5-1.5 mol. %

- material obtained by horizontal directional crystallization

- the material is a single crystal in the form of a plate with dimensions of at least 50 × 80 × 20 mm.

The solution of the problem of the invention is realized by the example of materials of binary systems forming a continuous series of solid solutions, the synthesis of which opens up the possibility of directional control of the sensitivity of these materials to ionizing radiation of various types within the same system and allows you to determine the range of the chemical composition of the material with maximum sensitivity to radiation of γ-quanta.

This is done by synthesizing high-density (ρ at least 7.8 g / cm ³ ) binary systems with large Z values (at least 90) of materials based on heavy metal fluorides that can be used with great efficiency as “heavy” scintillators in systems for detecting γ-ionizing radiation, in particular in electromagnetic calorimeters.

To implement the above problem, two binary systems with existing rows of continuous crystalline solid solutions are considered. The first is the binary system LiYF ₄ - LiLuF ₄ ; the second is the BaY ₂ F ₈ - BaYb ₂ F _{8 system} . In these binary systems, respectively, rows of crystalline solid solutions are formed with empirical formulas Li (Y _1-x Lu _x ) F ₄ and Ba (Y _1-x Yb _x ) ₂ F ₈ in the range of molar fractions of x from 0.01 to 0.9. High values of the integrated light output are ensured by activating single crystals with Ce ³⁺ or Pr ^{3 +} ions.

Single crystals are grown by horizontal directional crystallization (SOC) in graphite “boat” containers in a fluorinating argon atmosphere. The existing setup allows one to grow single crystals up to 400 × 500 × 40 mm in size and to create high-aperture large-volume scintiblocks for electromagnetic calorimeters (EMC). Such large-sized elements (in contrast to small-sized several cubic centimeters, usually obtained by the Bridgman-Stockbarger method) are of particular interest for modern research in the field of high-energy physics in that they are sensitive to weak electromagnetic fields and can completely absorb photons of γ radiation with energy up to 1 MeV.

The present invention uses the phenomenon of disordering of the crystal structure of inorganic fluoride compounds of solid solutions of binary systems LiYF ₄ -LiLuF ₄ and BaY ₂ F ₈ -BaYb ₂ F ₈ to control the physical parameters of scintillation crystalline materials, such as effective atomic number (Z) and density (ρ ) determining the efficiency of using these materials in γ-radiation detectors. Unlike simple crystals with a strictly stoichiometric composition (LiYF ₄ , LiLuF ₄ , BaY ₂ F ₈ , BaYb ₂ F ₈ ), which have fixed characteristic values of the above parameters, in the compositions of crystalline solid solutions with empirical formulas Li (Y _1-x Lu _x ) F ₄ and Ba (Y _1-x Yb _x ) ₂ F ₈ it is possible to monotonically change the effective atomic numbers Z in a wide range of molar fractions of “x”, towards larger or smaller values, depending on for which detector of ionizing neutron radiation or γ required to obtain a scintillator.

The drawing shows the calculated data Z depending on the molar fractions of x for "heavy" Li (Y _1-x Lu _x ) F ₄ - curve 1 and even more "heavy" scintillators Ba (Y _1-x Yb _x ) ₂ F ₈ - curve 2, which can be synthesized in a series of solid solutions of the systems indicated above. The maximum Z values of these compounds in the range of molar fractions of 0.5 <x <0.7 reach 92 and 124, respectively, which is much higher than that of the well-known PbWO ₄ scintillator (Z = 73) currently used in the Large Hadron Collider ( LHC) in CERN [MS Ippolitov et al., "Studies of lead tungstate crystals for the ALICE electromagnetic calorimeter PHOS" in Nuclear Instruments and Methods in Physics Research A 486 (2002), p. 121-125]. Thus, for example, the “light” scintillator LiYF ₄ (Z = 40), known as a neutron radiation detector, by adding a small amount of 5% LuF ₃ to it during synthesis, will turn it into “heavy”, increasing its Z from 40 to 75 (drawing), which is comparable with PbWO ₄ (Z = 73).

Thus, in the range of solid solutions under consideration, in a wide range of molar fractions of “x,” one can set the parameter Z to synthesize the desired composition of the scintillation material, depending on the problem of detecting the required type of radiation, and vice versa, to synthesize a crystalline scintillator of a specific crystal chemical composition with a given parameter Z .

In addition, solid solutions Li (Y _1-x Lu _x ) F ₄ (x = 0.5-0.7) have a greater isomorphic capacity with respect to the ions of the cerium subgroup than simple crystals LiYF ₄ and LiLuF ₄ . This allows you to create bright scintillators with high values of radiation intensity I _izl. due to the possibility of introducing large concentrations of Ce ³⁺ (or Pr ³⁺ ) ions into the crystal lattice of solid solutions. The characteristics of ρ, Z and I _rad viewed crystals of solid solutions of various compositions mixed with an admixture of Ce ³⁺ or Pr ³⁺ (integral light yield can reach up to 27,000 photons / MeV) is considerably superior to known scintillators PbWO ₄ (200 photons / MeV) [MS Ippolitov , et al., "Studies of lead tungstate crystals for the ALICE electromagnetic calorimeter PHOS" in Nuclear Instruments and Methods in Physics Research A 486 (2002), p. 121-125], and in terms of speed τ _rad = 10-15 ns is practically not inferior to the latter.

Examples of obtaining scintillation materials in the form of single crystals of solid solution compounds with the general formulas Li (Y _1-x Lu _x ) F ₄ and Ba (Y _1-x Yb _x ) ₂ F ₈ activated by Ce ³⁺ ions. (With the introduction of another activator ion - Pr ^3+, the synthesis process will be similar, since these ions are introduced in the form of small impurities of not more than 0.5-1.5 mol.% And do not affect the growth process).

Single-crystal materials are solid solutions (mixed crystals) with a disordered structure, crystallizing in binary systems of simple compounds with an ordered structure based on LiYF ₄ - LiLuF ₄ (tetragonal with scheelite structure, _space group C _64h ) and BaY ₂ F ₈ - BaYb ₂ F ₈ (monoclinic, space group C _22h ). The mixed crystals corresponded to the empirical formulas Li (Y _1-x Lu _x ) F ₄ and Ba (Y _1-x Yb _x ) ₂ F ₈ , with molar fractions of "x" up to 0.7.

Monoclinic crystals of solid solutions of Ba (Y, Yb) ₂ F ₈ : Ln ³⁺ (where Ln ³⁺ = Се ³⁺ or Pr ³⁺ ) were grown by GNC in graphite boats in a growth unit with a resistance heater in a graphite thermal unit. (For example, according to patent No. 2320789). The mixture composition of the reagents of the brand OSCH (mol.%): 36.2 BaF ₂ ; 53.7 YF ₃ ; 9.6 YbF ₃ and 0.5 CeF ₃ (or PrF3) were placed in a graphite crucible and dried in a chamber of a growth unit in vacuum (0.005 torr) at a temperature of 250 ° C for 24 hours. The atmosphere for the crystal growing process was prepared by burning tetrafluoroethylene in argon gas with a purity of 99.99% at a pressure of 985 torr. Then, the initial mixture was heated to its melting point and maintained at a temperature of about 1020 ° C for 6 hours. The crystal was grown onto a seed of arbitrary orientation at a speed of 1.5 mm / h. The obtained crystalline samples had the form of volumetric plates with a cone in the bow with an average size of 50 × 80 × 20 mm. The crystals were transparent and of good optical quality.

A similar technique was used to grow tetragonal crystals of solid solutions of Li (Y, Lu) F ₄ : Ln ³⁺ compounds. The composition of the mixture from the OSCh reagents corresponded (mol%): 12 LiF; 24.5 YF ₃ ; 62 LuF ₃ and 1.5 CeF ₃ (the same for PrF ₃ ). In contrast to the first case, the crystal growth was carried out on oriented seeds along and perpendicular to the 4th order axis.

Claims (11)

1. scintillator material for registration of ionizing radiation, which is a crystalline solid solution with the empirical general formula Li (Y _1-x Lu _x) F ₄ with x = 0.01-0.8, resulting in a binary system LiYF ₄ -LiLuF _4. 2. The material according to p. 1, characterized in that for the registration of neutron radiation x = 0.01. 3. The material according to p. 1, characterized in that for the registration of x-ray and γ-radiation x = 0.5-0.7. 4. The material according to paragraphs. 1-3, characterized in that it is activated by Ce ³⁺ or Pr ³⁺ ions in an amount of 0.5-1.5 mol.%. 5. The material according to claim 1, characterized in that it is obtained by the method of horizontal directional crystallization. 6. The material according to claim 1, characterized in that it is made in the form of a single crystal in the form of plates with dimensions of at least 50 × 80 × 20 mm. 7. Scintillation material for recording ionizing radiation, which is a crystalline solid solution with the general empirical formula Ba (Y _1-x Yb _x ) ₂ F ₈ at x = 0.01-0.9, formed in the binary system BaY ₂ F ₈ - BaYb ₂ F ₈ . 8. The material according to p. 7, characterized in that for the registration of x-ray and γ-radiation x = 0.5-0.7. 9. The material according to paragraphs. 7-8, characterized in that it is activated by Ce ³⁺ or Pr ³⁺ ions in an amount of 0.5-1.5 mol.%. 10. The material according to p. 7, characterized in that it is obtained by the method of horizontal directional crystallization. 11. The material according to p. 7, characterized in that it is made in the form of a single crystal in the form of plates with dimensions of at least 50 × 80 × 20 mm.

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