The single crystals of lead tungstate

 

(57) Abstract:

The single crystals of lead tungstate obtained by use of tungsten trioxide and lead dioxide or lead tungstate, in which lanthanum is contained in an amount of from 3 x 10-7mol to 10 x 10-3mol to one mol of lead tungstate. It is possible to obtain single crystals of lead tungstate. The technical result is to obtain crystals, which are used as a scintillator for radiation detector capable of increasing the amount of light by increasing the transmittance of light and reduction of self-absorption. 2 Il.

The present invention relates to single crystals of lead tungstate used as a scintillator in the detector for the emitted rays, such as x-rays or gamma-rays.

The scintillators for use in high power consumption must have certain characteristics, among which are particularly important are:

(1) high density,

(2) short afterglow,

(3) exceptional radiation hardness.

As materials satisfying the above requirements, still ispolzuemyi higher performance. In view of the above have been investigated by various substances with the aim of finding those substances that have the characteristics of more high efficiency, and it was found that among such substances for the detection of radiation is applied to the lead tungstate PbWO4. Then research was conducted in order to obtain single crystals of PbWO4measurements of their characteristics and their implementation in practical operation.

Typically, the single crystals of PbWO4get by way of extrusion with rotation (Czochralski method). That is, the lead oxide (PbO) and tungsten trioxide (WO3or PbWO4used as source material and melted in a platinum crucible and receive crystals PbWO4by the Czochralski method.

A method of obtaining single crystals PbWO4described in the publication Arora, S. K. et.al. Flux growth and elektrical properties of PbWO4cristals "J. Crist. Growth" 1982, 57, N 2, pp. 452-455. There is described a single crystal PbWO4obtained from the flow of Na2WO4having high dielectric, electrical and microtopographical characteristics. However, this source according to the prior art does not contain any information about how to use crystals PbWO4as scin, the known scintillation characteristics of lead tungstate described, for example, in the publication "Scintillation Characteristics of PbWO4Single Cristals at Room Temperature (M. Kobayashi et.al. Nuclear Instruments and Methods in Physics Research A 333 (1993) pp. 429-433. Such single crystals of lead tungstate as the single crystal produced by the Czochralski method, has the following disadvantages.

PbWO4received so far, mainly satisfies the three above-mentioned characteristics. However, since the source material does not have sufficient purity, single crystal is injected impurities, giving yellow crystals. In single crystals of PbWO4peak radiation corresponds to approximately 400-420 nm. However, since the yellow color absorbs light at a wavelength of about this peak, the radiated light is partially absorbed by the crystals by self-absorption, and light loss is inevitable when the output light from the crystals.

For PbWO4light output is about 3% of the light output in Bi4Ge3O12(value for PbWO4includes self-absorption).

PbWO4surpasses the existing Bi4Ge3O12from the point of view of the three aforementioned characteristics, but gives less radiation. So izklyuchitelen have been made various attempts to reduce the coloration of the crystals. One of them is to increase the purity of the source material, but a satisfactory result is not obtained even when receiving PbWO4by increasing the purity of the source material up to 99,999%. On the other hand, to achieve opacity also tried to use alloying impurity, but this too failed. With the addition of molybdenum, it turns out that the magnitude of the radiation is increased in areas of weak radiation, but this amount of radiation is identical to that which is obtained from the crystals without additives in the field of strong radiation, and moreover, the addition of molybdenum affects the time of the afterglow.

As mentioned above, the reduction coloring crystals without compromising other characteristics has not yet been reached.

The accelerators used in the field of high energy, require more energy. Then, to get a higher time resolution is required scintillator for radiation detectors. Therefore, the crystals used to create the scintillator must also have less time afterglow (preferably less than a few nanoseconds) and high stiffness radiation (preferably more than 108rad.). On the other hand, from the point of view chuvstvitelniy PbWO4obtained at the present time, does not satisfy this requirement.

The invention is intended to solve the above problems, and its objective is to develop the single crystals of lead tungstate, is used as the scintillator used for radiation detectors.

In accordance with the present invention, the above problem can be solved using single crystals of lead tungstate obtained by use of tungsten trioxide and lead oxide or lead tungstate containing lanthanum in an amount of from 3 to 10-7mol to 10 10-3mol to one mol of lead tungstate.

The above and other features and advantages of the present invention are explained in the following description of preferred specific embodiments of the invention with reference to the accompanying drawings, where

in Fig. 1 depicts a graph showing the relationship between wavelength and transmittance,

Fig. 2 is a graph showing the relationship between the concentration of lanthanum and the degree of increase in the transmittance.

As a result of serious studies of single crystals of PbWO4with little campagnole reduction in the range of 420 nm, indicates that the absorption is large, and the curve near the end of the absorption takes place hollow, as shown in Fig. 1. On the other hand, the curve of the transmittance of single crystals of PbWO4that added lanthanum, has no such lowering of about 420 nm, indicating that the absorption is small, and the curve drops sharply near the end of the absorption and indicates that the characteristic is satisfactory. Based on these discoveries have conducted various experiments and the obtained single crystals of lead tungstate according to the invention.

In single crystals of PbWO4the amount of available light can be increased by increasing the light transmittance and reduce the attenuation through the introduction of lanthanum in an amount of from 3 to 10-7mol to 10 10-7mole to one mole of the PbWO4.

If the concentration of lanthanum is 3 to 10-7mole or less, appears the absorption due to staining, whereas if the concentration is 10 to 10-3mole or more, you receive black color due to the fact that the lanthanum causes the total self-absorption and deteriorates the transmittance.

PbO and WO3or PbWO4used as source material and melt when heat is the tall PbWO4is from 3 to 10-7mol to 10 10-3mole to one mole of the PbWO4.

For this purpose, the content of lanthanum present in the PbO and WO3or PbWO4used as the source material is set to 3 to 10-7mole or less. In addition, the total number of impurities, including lanthanum contained in the PbO and WO3or PbWO4set equal to 1 to 10-4mole or less, preferably 10-5mole or less.

When thus obtained the crystals of PbWO4give a pre-determined size, is subjected to mirror polishing and see the light transmittance curve of the transmittance does not decrease to about 420 nm and drops sharply in the vicinity of the end of the absorption curve, which indicates high performance.

Example 1

After the PbO powder and powder WO3, purity from 99.99% of everyone weighed each in equimolar amounts and mixing them, the mixture was loaded into a platinum crucible with a diameter of 70 mm and a height of 70 mm and a melted mixture of the source of powder material by induction heating, and then by the Czochralski method received from molten liquid crystals PbWO4as with the number 3 10-7mol. The content of lanthanum in the PbO powder and WO3was 5 10-8or less.

Thus obtained crystals PbWO4cut with dimensions HH cm, and was subjected to mirror polishing, and then measured the transmittance in the range of 300-600 nm in the direction of thickness 1 cm

The measurement results shown in Fig. 1 and Fig. 2. In Fig. 1 shows the relationship between wavelength and transmittance, and Fig. 2 shows the relationship between the concentration of lanthanum and the degree of increase in the transmittance.

The curve of the transmittance did not decrease to about 420 nm and showed a sharp decline near the end of the absorption curve. The transmittance was equal to 70.5% at a wavelength of 420 nm, which shows an increase of 19.5%.

Example 2

After the PbO powder and powder WO3, purity from 99.99% of everyone weighed each in equimolar amounts and mixing them, the mixture was loaded into a platinum crucible with a diameter of 70 mm and a height of 70 mm and a melted mixture of the source of powder material by induction heating, and then by the Czochralski method received from molten liquid crystals PbWO4in the form of a rod with a diameter of 33 mm and a length of 70 mm Lanthanum d is tan powder of PbO and WO3was 5 10-8or less.

Thus obtained crystals PbWO4cut with dimensions HH cm, and was subjected to mirror polishing, and then measured the transmittance in the range of 300-600 nm in the direction of thickness 1 cm

The measurement results shown in Fig. 1 and Fig. 2. The curve of the transmittance did not decrease to about 420 nm and showed a sharp decline near the end of the absorption curve. The transmittance was 71% at a wavelength of 420 nm, which shows an increase of 20.3%.

Example 3

After the PbO powder and powder WO3, purity from 99.99% of everyone weighed each in equimolar amounts and mixing them, the mixture was loaded into a platinum crucible with a diameter of 70 mm and a height of 70 mm and a melted mixture of the source of powder material by induction heating, and then by the Czochralski method received from molten liquid crystals PbWO4in the form of a rod with a diameter of 35 mm and a length of 70 mm Lanthanum added in such quantity that he was present in the crystals in the amount of 7,5 10-4mol. The content of lanthanum in the PbO powder and WO3was 5 10-8or less.

Thus obtained crystals PbWO4resolution is not 300-600 nm in the direction of thickness 1 cm

The measurement results shown in Fig. 1 and Fig. 2. The curve of the transmittance did not decrease to about 420 nm and showed a sharp decline near the end of the absorption curve. The transmittance was 70% at a wavelength of 420 nm, which shows an increase of 18.6%.

Example 4

After the PbO powder and powder WO3, purity from 99.99% of everyone weighed each in equimolar amounts and mixing them, the mixture was loaded into a platinum crucible with a diameter of 70 mm and a height of 70 mm and a melted mixture of the source of powder material by induction heating, and then by the Czochralski method received from molten liquid crystals PbWO4in the form of a rod with a diameter of 35 mm and a length of 60 mm Lanthanum added in such quantity that he was present in the crystals of 3 to 10-3mol. The content of lanthanum powder PbO WO3was 5 10-8or less.

Thus obtained crystals PbWO4cut with dimensions HH cm, and was subjected to mirror polishing, and then measured the transmittance in the range of 300-600 nm in the direction of thickness 1 cm

The measurement results shown in Fig. 1 and Fig. 2. The curve of the transmittance did not decrease okolny 420 nm, that shows an increase of 16.9 %.

Since single crystals of PbWO4containing lanthanum in an amount of from 3 to 10-7mol to 10 10-3mole, have high transmittance and low absorption, emitted light can be output in the absence of absorption while passing through the crystals.

In the above experiment, the measurement was performed in the direction of thickness 1 cm, however, since in the actual application uses material length 23 cm, the difference in transmittance of 1 cm provides a particularly important influence in a state of practical application.

If the curve of the transmittance is lower in the range of about 420 nm, as in the known single crystals PbWO4the light at the wavelength of the radiation 400-430 mm is absorbed during the passage along the length of 23 cm and can hardly be brought out into the open in the form of a beam. Since the transmittance at a wavelength of 420 nm to 1 cm in existing single crystals PbWO4is 59%, the light after passing along the length of, for example, 23 cm can only be used by 1% or less of the magnitude of radiation.

However, since single crystals of PbWO4corresponding to this izobreteniya bandwidth of 1 cm is 70%, the value of the light transmittance is increased 50 times.

Therefore, the single crystals of PbWO4can be effectively used for practical use.

As described above, in accordance with the present invention it is possible to obtain single crystals of lead tungstate, which is applicable as a scintillator for radiation detector capable of increasing the amount of light emission by increasing the transmittance of light and reduction of self-absorption.

The single crystals of lead tungstate, characterized in that they are obtained by use of tungsten trioxide and lead dioxide or lead tungstate and contain lanthanum in an amount of from 3 x 10-7mol to 10 x 10-3mol to one mol of lead tungstate.

 

Same patents:

The invention relates to methods of obtaining crystals, namely the method of producing single crystals of lead tungstate (hereinafter PWO), and can be used in the manufacture of scintillation elements used in the detectors of ionizing radiation, high energy, working in conditions of high doses in tracts registration requiring high time resolution

Laser substance // 2066352
The invention relates to the field of quantum electronics and can be used in the development of lasers in the infrared range

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

The invention relates to materials and can be used to create managed functional devices

The invention relates to the field of scintillation materials used for registration and spectroscopie ionizing radiation

FIELD: chemistry.

SUBSTANCE: invention relates to growing high-temperature inorganic monocrystals and can be used in quantum electronics and elementary-particle physics, in particular for neutrinoless double beta decay detectors. The said monocrystals are grown by pulling zinc molybdate crystals ZnMoO4 from molten initial charge in a melting pot for inoculation. The initial charge used is a mixture of oxides ZnO and MoO3, taken in stoichiometric ratio with excess MoO3 in amount of 1.0-7.0 wt %, and growth takes place at crystallisation volume rate of over 0.4 cm3/h. Using Czochralski growth method, pulling rate is 0.3-3.0 mm/h with axial temperature gradient at the crystallisation front of 80-100°/cm. Using Kyropoulos growth method, pulling rate does not exceed 0.5 mm/h while maintaining crystal diametre of 80-95 % of the diametre of the melting pot.

EFFECT: proposed method allows for obtaining large monocrystals (size of 1 cm3 or more), with optical properties suitable for use as scintillation detectors and optical elements.

3 cl, 2 ex, 2 dwg

FIELD: physics.

SUBSTANCE: optical medium for converting monochromatic laser radiation with wavelength 975±5 nm to the 1483-1654 nm band is a complex calcium tetragermanate of erbium and yttrium of formula ErxY2-xCaGe4O12, where 0.1<x<0.3. The method of making the said optical medium involves preparation of two initial mixtures of components containing the following in wt %, respectively: calcium carbonate - 11.11; erbium oxide - 42.45; germanium oxide - 46.43 and calcium carbonate - 13.45; yttrium oxide - 30.34; germanium oxide - 56.21. Separate mixing of components of each mixture is carried out in the presence of an alcohol, as well as heating to 700-900°C and maintaining that temperature for 8-10 hours. Repeated heating is carried out to 1050-1100°C, while maintaining that temperature for 100-150 hours and reburdening every 20 hours. Both initial mixtures are then mixed in ratio of 1:4.6-15.3 in the presence of an alcohol and heating to 1050-1100°C and maintaining that temperature for 40-50 hours and reburdening every 10 hours.

EFFECT: possibility of converting monochromatic radiation into a band with simultaneous amplification during operation of the laser in continuous pumping mode.

2 cl, 3 dwg, 2 ex

FIELD: metallurgy.

SUBSTANCE: invention refers to growth from molten metal of non-alloyed crystals of sodium tungstate-bismuth NaBi(WO4)2 being perspective material for Cherenkov detectors. Growth of crystals is performed using Chokhralsky method in air atmosphere at drawing speed of 4-5 mm/hour and crystal growth speed of 15-19 min-1.

EFFECT: method allows obtaining crystals transparent in visible range beginning from wave length of 352 nm.

3 dwg, 4 ex

FIELD: chemistry.

SUBSTANCE: invention relates to the technology of growing lithium-magnesium molybdate Li2Mg2(MoO4)3 crystals. The method involves melting lithium-magnesium molybdate in a molten solvent, crystallising while cooling the melt and cooling the grown crystals, wherein the solvent used is lithium molybdate Li2MoO4 with molar ratio of lithium-magnesium molybdate to lithium molybdate Li2MoO4 of 2:3, respectively; crystallisation is carried out on an inoculating crystal revolving at a rate of 35 rpm, oriented on the [010] direction, rate of drawing rate of the inoculating crystal of 1-3 mm/day while simultaneously cooling the melt at a rate of 0.2-5 degrees/day and then separating the grown crystals from the melt and cooling at a rate of 30 degrees/hour.

EFFECT: method enables to obtain optically homogeneous lithium-magnesium molybdate crystals which do not contain inclusions, blocks and cracks.

FIELD: chemistry.

SUBSTANCE: invention relates to field of chemical technology and deals with obtaining volumetric crystals with composition Li8Bi2(MoO4)7. Crystals are grown from solution-melt of lithium-bismuth molybdate in solvent by crystallisation with gradual cooling of melt and grown crystals, and as solvent used is eutectic mixture, containing 47 mol.% of molybdenum oxide and 53 mol.% of lithium molybdate with content of lithium-bismuth molybdate and eutectic mixture equal 10-40 mol.% and 90-60 mol.% respectively, growing is performed under conditions of low temperature gradients, constituting less than 1 grad/cm, on primer, oriented by [001] and rotating at rate 20-30 rev/min with pulling rate 0.5-2.0 mm/day with constant cooling of solution-melt at rate 0.2-5.0 degree/day with further separation of grown crystals from solution-melt and cooling them to room temperature.

EFFECT: invention makes it possible to obtain large (with size 20÷30 mm) Li8Bi2(MoO4)7 crystals of high optic quality.

1 ex

FIELD: chemistry.

SUBSTANCE: invention relates to field of chemical technology, namely to growing crystals of potassium-barium molybdate K2Ba(MoO4)2 from solution-melt of K2Ba(MoO4)2 for analysis of physical properties and practical use. As solvent used is potassium molybdate K2MoO4, with molar ratio of potassium-barium molybdate and potassium molybdate K2MoO4, equal 1:2, respectively, crystallisation is carried out on seed, increased from 1 to 2 mm/day and rotating at rate 30-40 rev/min, oriented by direction [001], cooling of melt is carried out at rate from 0.2 to 3 degrees/day, with cooling of crystals being carried out at rate 20 degrees/day.

EFFECT: claimed method makes it possible to obtain optically homogenous K2Ba(MoO4)2, crystals of large size (25×15 mm) without inclusions, blocks and cracks.

1 ex

FIELD: chemistry.

SUBSTANCE: invention refers to chemical technology and concerns manufacturing crystals of rubidium-bismuth molybdate RbBi(MoO4)2. The crystals RbBi(MoO4)2 are grown from a high-temperature solution in melted charge containing rubidium dimolybdate and triple lithium-rubidium-bismuth molybdate LiRbBi2(MoO4)4, in ratio of the latter toribidium dimolybdate equal to 10-40: 90-60 mole %, respectively; fuse crystallisation is focused in the direction [001], with a fuse rotation at 30-65 rpm and pulling rate 0.3-1.0 mm/day with cooling the melted solution at 0.2-1.0 degrees/day; the growing process in performed in the environment of low gradient ΔT less than 1 degrees/cm in the melted solution.

EFFECT: invention enables producing the coarse crystals RbBi(MoO4)2 of high optical quality.

1 ex

FIELD: chemistry.

SUBSTANCE: invention relates to the field of the chemical technology of growing sodium-bismuth molybdate NaBi(MoO4)2 crystals for the research of physical properties and practical application. The monocrystals NaBi(MoO4)2 are grown by crystallisation from a high-temperature solution in a charge melt, which contains sodium-bismuth molybdate and a solvent sodium dimolybdate in a ratio, equal to 10-30:90-70 mol% respectively, crystallisation is carried out on inoculum, oriented perpendicularly to dipyramide edges [101], with the inoculum revolving at a rate of 10-30 rev/min and a rate of extension of 1-5 mm/day, with constant cooling of the solution-melt at a rate of 0.5-15 degrees/day, with growing being carried out under conditions of low gradients ΔT/Δl lower than 1 degree/cm in the solution-melt.

EFFECT: method makes it possible to obtain colourless, stoichiometric in the structure, large (size 75×30 mm), optically homogenous NaBi(MoO4)2 crystals.

1 ex

FIELD: nanotechnology.

SUBSTANCE: invention relates to production of nanocrystalline powders of chemical compounds and can be used for production of radiation shields, photocatalytic and scintillation materials. Superfine nanocrystalline lead tungstate (PbWO4) is prepared by a chemical reaction between a solution of lead acetate and sodium tungstate with 5-20 % solution of lead acetate Pb(CH3COO)2·3H2O, prepared by dissolving lead acetate in a mixture of water and ethanol or acetone at a ratio of 1.5-1:1, dispersed as fine droplets, added to 2.5-10 % aqueous solution of sodium tungstate Na2WO4·2H2O on its surface with its continuous stirring. Disclosed method has a higher rate of yield and smaller dimensions of required equipment, due to lower consumption of solvents in preparation of solutions (5-10 times). Method also eliminates need for additional substances - dispersants, having limited application in industry.

EFFECT: technical result of invention is to obtain nanocrystalline PbWO4, having average particle size of about 50 nm.

1 cl, 2 dwg

FIELD: chemistry.

SUBSTANCE: method ofproducing fine-grained barium titanate comprises treating a mixture of titanium dioxide and barium oxide powders with water vapour in a reactor in a static mode under supercritical conditions: at a temperature of 380 to 420°C and a pressure of 22.5 to 30.5 MPa for 16-48 hours, after which the reactor is cooled to room temperature, the resulting barium titanate is first dried at a temperature of 70±20°C for 10-12 hours, washed with a solution of acetic acid with a concentration of 5-10 wt %, then with distilled water and again dried at a temperature of 70±20°C to constant weight.

EFFECT: invention makes it possible to produce single-phase barium titanate with a crystal size of 40-300 nm with a high content of the basic substance.

3 cl, 8 dwg, 2 tbl, 8 ex

Up!