Scintillation material

 

(57) Abstract:

The invention relates to techniques for registration and spectrometry of ionizing radiation, in particular for scintillation materials. The purpose of the invention is the creation of scintillation material based on double tungstate of sodium - bismuth, with the increased light output of the scintillation. Crystal N aBi(WO4)2includes the additional admixture of alkali metal from the group of Li, K, Pb, Cs in the amount of 0.005 to 0.3 wt.%. The introduction of alkali metals in the scintillation material leads to an increase of the light output of the scintillation, which helps to widen the scope of its application. table 1.

The invention relates to techniques for registration and spectrometry of ionizing radiation, in particular for scintillation materials.

The known scintillation crystals wolframates, in particular cadmium tungstate CdWO4(CWO) [1] advantages of the CWO, a scintillator, are high density (7 g, 9 g/cm3), high effective atomic number (Z 62), small radiation length (1,10 cm), significant light output of the scintillation (up to 40% with respect to NaT(Tl), a large enough wavelength maximum of the emission spectrum (= 480-540 nm), m CWO is significant excitation time of the scintillation pulse, forming at room temperature of about 12000 NS (pulse there are two components with constant time 5000 and 20000 NS). In addition, the CWO crystals have low radiation resistance. So, when irradiated by photons of average energy (E To 0.662 MeV) reduced their light yield depending on the absorbed dose at 0.3 percent GSR. These factors limit the application of the scintillator CWO in the detection of ionizing radiation of high energy and tracts registration requiring high time resolution.

Closest to the invention is a crystal of double tungstate of sodium-bismuth NaBi(WO4)2used in radiators of Cherenkov detectors [2]

The advantages of this material, as a medium, converts the energy of ionizing radiation in quanta of light is determined by its high density (EUR 7.57 g/cm3), a large effective atomic number (Z71), small radiation length (1,01 cm), high optical transparency in the visible and ultraviolet (except for the area 300-410 nm) ranges, speed (of the order of 3 NS) and significant radiation resistance decrease in optical transmittance occurs at doses of irradiation over 80 kGy and does not exceed 0.15% scintillator same crystal NaBi(WO4)2unsuitable for detection of quanta, which is determined by a slight scintillation light output not exceeding at E= To 0.662 MeV 0.2% on scintillator NaT(Tl).

The purpose of the invention is the creation of scintillation material based on double tungstate of sodium-bismuth, with the increased light output of the scintillation.

The objective is achieved by the fact that the crystal NaBi(WO4)2includes the additional admixture of alkali metal from the group of Li, K, Pb, Cs in the amount of 0.005 to 0.3 wt.

The choice of these alkali metal as a dopant due to the following. It is known that the scintillation wolframate belong to the class of so-called someactivity scintillators. Their radioluminescence is due to the radiative disburdened anionic complex WO42-and almost indiferente to the presence of cations. When this glow wolframates is not all anions WO42and only the part of them that is irregular lattice sites, i.e. in distorted sites anionic sublattice. Double tungstate of sodium-bismuth crystallizes in the scheelite structure, the cations Na1+and Bi3+have IBEC's direct this to. PM almost equal physical ionic radii rNa1+= 1,32 and rBi3+ 1,31 . These factors contribute to a small degree of local distortion WO42-complexes (WO4tetrahedron weakly compressed along the axis and has two ribs on 2,97 and four ribs on 2,87 , that is, the difference does not exceed 3.4%). To create a local distortion WO42complexes sufficient to enhance light output of the scintillation NaBi(WO4)2allows the replacement of part of the cations Na1+or Bi3+admixture with non-replaceable cation ionic radius. It is necessary that the mixture had the same type of chemical bond and the ability isovalent to replace the corresponding cations preserving K. 8 o'clock. These requirements can be met by the substitution in NaBi(WO4)2sodium ions to monovalent ions of alkali metals Li, K, Pb, Cs, for which K. H. 8 allowed.

The single crystals of the scintillator NaBi(WO4):Me, where IU is taken from the group of metals of Li, K, Pb, Cs, obtained as follows. The initial charge consists of a mixture of components Na2CO3:B2O3:WO3with the addition compounds of alkali metal from the specified group. The single crystals grown by the Czochralski method vu rotation of the seed 20-30 min-1. At the end of the cultivation process cooling crystals are at a rate of 50 K/h

The obtained single crystals controlled by the impurity content of the alkali metal, the magnitude of the light output of the scintillation, the decay time of the pulse and the radiation resistance. When using, respectively, the method of atomic absorption analysis, a standard method of measurement of their light yield peak total absorption-ray source

137Cs, one-electron method in the excitation-particles from the source

238Pu and measurement of the optical transmittance of the samples before and after irradiation with a fixed dose from source 60Co.

P R I m e R s. The initial charge was prepared from a mixture of the main components of Na2CO3:Bi2O3:WO3. For hanging the main charge was introduced additives of alkali metals in the form of carbonates IU2CO3where IU Li, K, Pb, Cs. Of the compounds by the Czochralski method were grown crystals of NaBi(WO4)2:Me. The crystals obtained in the range of concentrations of impurities of alkali metals up to 0.3 wt. transparent, have a yellow mild to moderate intensity, color, contain a small number of visually observable defects (tankadin 60-80 mm. When the dopant content of 0.35 or more wt. the presence of inclusions and fracture of the crystals increase dramatically, which is associated with loss of phase, is chemically and structurally significantly different from the matrix. Such samples are not transparent in the whole volume.

To measure the scintillation characteristics of the crystals produced items with a diameter of 18 and a thickness of 5 mm, the ends of which were polished, class Rzof 0.025, and the side surface is frosted. Additional samples were taken of the material to control the alloying content of the alkali metal. On the manufactured items are also controlled by the optical transmittance spectra of the radiation resistance of the material. The spectra were taken on a spectrophotometer at a wavelength of 480 nm before and after irradiation of the element from the source-quanta with the energy of 1.33 MeV (60Co) doses of 12.0 Mrad. The results of measurements of the concentrations of impurities, the light output of the scintillation, the decay time of impulse and change of optical transmittance in the table.

The table shows that the positive effect achieved with the introduction of the specified quantity of alkali metals in the crystals of NaBi(WO4)2is that the obtained scin is 0.1 wt. in the case of additives Li 2,1, K 1,65, 1,0 Pb, Cs of 0.8% with respect to NaT(Tl), i.e. respectively 10.5; 8,2; 5,0; 4.0 times higher than that of undoped crystal. However, the imposition of alkali metals in the concentration range of 0.005-0.3 wt. has not led to a deterioration in the performance and radiation resistance of the crystal with respect to material described in the prototype. The effect of increasing their light yield is not achieved when the content of impurities of less than 0.005 and large 0,3 wt. (examples of 1.5, 12 and 16 with the introduction of impurities with minimal (Li) and maximum (Cs) ionic radii). In the first case this is due to the small magnitude of the substitution in the crystal matrix of sodium ions on the ion impurities. In the second due to the opacity of the crystal, which prevents the release of light scintillations. Thus, the range of impurity concentrations of the alkali metal from the group of Li, K, Pb, Cs, ensuring the achievement of the objectives, ranges from 0.005 to 0.3 wt.

The obtained scintillator material due to the improvement in important characteristics of the light output of the scintillation has a relatively large material described in the prototype, the application range. The scintillation crystal may find use for registration spectrometry particles and kVA is her colliding beams. In this case, increased their light yield will provide an increase in sensitivity of the recording system, and a small excitation time and a significant radiation resistance will provide a high temporal resolution and the ability to work in radiation fields of great intensity.

The SCINTILLATOR MATERIAL on the basis of double tungstate of sodium-bismuth NaBi (WO4)2, wherein the material further comprises a mixture of alkali metal from the group LiK, Rb, and Cs in the amount of 0.005 to 0.3 wt.

 

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