Scintillation material

 

(57) Abstract:

The invention relates to the field of scintillation materials used for registration and spectroscopie ionizing radiation. The material on the basis of Trichogramma bismuth contains a mixture of ytterbium in the amount of 0.07 to 1.50 wt.% wt. Achieved the excitation time of the scintillation pulse = 16 NS, which is at 18.7 times less than without the addition of ytterbium in the material. Crystals were obtained by Czochralski method. table 1.

The invention relates to techniques for registration and spectrometry of ionizing radiation, specifically to the field of scintillation materials.

The single crystals of Trichogramma bismuth Bi4Ge3O12(BGO) is known as scintillation material used in various devices for detecting ionizing radiation.

Known BGO crystals grown by the methods of the Czochralski method, zone melting, growth from the melt of oxides of Bi2O3-GeO2, which is responsible stoichiometric Bi4Ge3O12[1]. This material is a true scintillator, i.e., do not contain adjuvants. Its scintillation properties due to the electronic transition3component with time constant = 300 to 310 NS, thus the contribution of the afterglow matrix minor (after 3 MS of no more than 0.005% of the peak intensity of the pulse), which prevents the application of the scintillation material in the recording devices ionizing radiation, requires a time resolution of less than 300 NS.

Closest to the proposed laser is monocrystalline material on the basis of Bi4Ge3ABOUT12containing as an activator of the laser properties of the admixture of ytterbium (Yb), introduced in the initial charge in the form of oxide Yb2O3at concentrations 2,0; 4,0; 4,5 wt.% [2].

Accordingly, the presence of Yb in the crystals was 1.76; 3,51, and 3.95 wt. % . The suitability of the use of this material in the specified quality is determined by the fact that the BGO crystals containing impurity in the range of 1.76-3,95 wt. % , a higher yield of luminescence under photoexcitation, which increases with the concentration of the activator.

Upon excitation of these crystals ionizing radiation is observed delay scintillation pulse to 350 NS, and the emergence of intensive long afterglow exceeding afterglow undoped BGO.

Thus the doped BGO iterb the ptx2">

The aim of the invention is the creation of a scintillation material with low excitation time of the scintillation pulse.

This goal is achieved by the fact that the scintillator material on the basis of Trichogramma bismuth, contains a mixture of ytterbium Yb: 0.07 to 1.5 wt.%.

The choice of ytterbium Yb as an impurity that can achieve the goal, due to the presence of ions in Yb3+intensive f ->> f, f ->> d and other absorption transitions localized in the region of the long wavelength edge of intrinsic absorption matrix Bi4Ge3O12and its luminescence, the possibility of charge exchange ions Yb3+to the state of Yb2+and small ionic radius Yb3+(0,858 ), facilitating its entry into BGO as structural impurities. The combination of the first two factors makes possible intensive energy exchange between the matrix and type impurity center with the formation of the effective channel extinguishing self-luminescence BGO, as well as the appearance of additional short-lived component of the scintillation pulse. The mechanism of quenching is caused by the capture carmelitano electron (e) in the conduction band and is carried out according to the scheme:
) occurs through virtual form (Yb3+)-due to the intracenter population nonradiative transitions of ions (Yb3+)-with the further capture of holes (h) of the valence band.

With increasing concentration of Yb in BGO growing share of the decay state of the ions (Yb3+in the conduction band that tightens the far stage of the scintillation pulse. This process, the contribution of which becomes dominant when the contents Yb over to 1.76 wt.%, masks the effect of nonradiative channel suppression and lengthens the scintillation pulse to 350 NS and more. This, along with the advent of long afterglow matrix limits the upper value of the interval of concentrations of impurities Yb.

The single crystal scintillator material was obtained as follows. From a mixture of oxides of Bi2O3and GeO2prepare the initial charge composition corresponding to the stoichiometry of Bi4Ge3O12or use as a source charge pre-synthesized crystalline triorthogonal bismuth. To the original charge add a certain amount of oxide of ytterbium (Yb2O3). In this case, applying high-purity substances intended for monokristalla is of Onna impurities. Growing single crystals from charge carried out by the Czochralski method from platinum crucibles in an oxidizing atmosphere at 1000-1100aboutAnd the speed of the crystal pulling 0.1 to 0.4 cm/h After the end of the process cooling are at a rate of 50 K/h, resulting in the formation of loose crystals.

Measuring the decay time of the scintillation material spend one-electron method in the excitation-particles from the source 238Ri on the installation, including two photomultiplier, the shapers of start and stop pulses, the time-amplitude Converter and a multichannel amplitude analyzer AI-1024. By known standard methods when excited by photons from the source137Cs control the light output of the scintillation and its energy resolution of the crystals. Additionally, non-destructive x-ray radiometric method determines the content of Yb in the scintillation material.

P R I m m e R. the Initial charge was prepared from a mixture of oxides of Bi2O3and GeO2taken in a mass ratio of 3:1. Five sub-samples of the original charge was injected additive oxide of ytterbium Yb2O3the number 0,011; 0,080; 0,6; 1,7; 2,0 wt.%. From the data the values along the axis of extrusion, not contain cracks and mechanical stresses. The length of the crystals up to 120 mm Of crystals for measurements made cylindrical elements height and 15 mm in diameter, one of the end faces are polished class of PZ0,025, the rest of the surface was frosted. The results of measurements of the concentrations of Yb in crystals, the decay time of the scintillation pulse, light output and energy resolution are shown in table. Also shown scintillation parameters of the crystal Bi4Ge3O12grown in the same way, not containing added ytterbium.

The table shows that the positive effect achieved with the introduction of the specified quantity Yb impurities in crystals of BGO, is that the obtained scintillator material has a low excitation time of the scintillation pulse constituting the optimal content of the additive Yb 0.5. %, = 16 NS, i.e. at 18.7 times less than that of undoped Bi4Ge3O12and in 21.9 times less than that of the laser material. In this case, the share of energy displayed in the short component is 70% of the total energy of the scintillation pulse. At a concentration of 0.01 wt.% the share of short components is small (not b is that irrelevant to improve the performance of the detectors. The excess concentration of Yb more than 1.5 wt. % leads to a decrease of their light yield, deterioration of energy resolution and increase the decay time of that limit specified value and upper range value of the contents of impurities.

Thus the range of concentrations Yb impurities in crystals of BGO is 0.7-1.5 wt.%. Moreover, in this interval there is no significant change other basic scintillation properties of the material.

The obtained scintillator material due to the improvement in the important characteristics is the decay time of the scintillation pulse has a relatively large BGO content Yb 1,76-3,95 wt.%, and the original Bi4Ge3O12range of use as a scintillator. The material will find use in high energy physics to create a device registration and spectrometry of ionizing radiation requiring high time resolution, in particular, in the registration systems of particles and quanta in flows of high density, for x-ray plasma diagnostics, scintillation blocks electromagnetic calorimeters, etc..

The SCINTILLATOR MATERIAL on the basis of Trichogramma bismuth containing PR is the air traffic management scintillation pulse, the material contains ytterbium in the amount of 0.07 to 1.50 wt.%.

 

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1 ex

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1 ex

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1 ex

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