Gamma-diffraction for Quartz Crystals
Development of Gamma-ray Diffactometry Method and the Equipment for Non-destructive Dislocation Density Control in Massive Quartz Crystals
Tech Area / Field
- INS-MEA/Measuring Instruments/Instrumentation
3 Approved without Funding
GNPO Polyus, Russia, Moscow
- Nuclear Physics Institute, Russia, Leningrad reg., Gatchina\nAll-Russian Research Institute of Automatics, Russia, Moscow
- SAWYER Research Products, Inc., USA, OH, Eastlake\nEuroTec GmbH, Germany, Berlin\nMitsubishi Materials Corporation, Japan, Tokyo
Project summaryIn high-quality communication apparatus, VCRs, electronic clocks, tape recorders, computers, record-players, toys, UHF-stoves and in other domestic appliances, piezoelectric devices are used, the parameters of which are governed by the quality of quartz used in them.
The number of dislocations in synthetic quartz can exceed 1000 cm-2. The necessity of dislocation density limitation increases with the use of planar manufacturing technology of piezoelectric elements with the application of chemical and ion-plasma etching techniques. The existing methods are destructive and don't enable to objectively evaluate dislocation concentration in crystals.
Therefore the development of a nondestructive method of control for dislocation density in quartz crystals seems to be reasonable. The most promising seems to be crystal investigation by employing gamma-ray diffractometer. Gamma-radiation passes through quartz crystals practically without absorption and it is insensitive to the surface state, therefore no surface treatment is required, and which makes it possible to obtain information of structural perfection of the crystal bulk.
The method employing diffraction of highly monochromatic gamma-radiation at crystals, is near in its ideology to that of double-crystal X-ray diffractometry, possesses a number of substantional advantages: high penetrability of gamma-quanta, high absolute angular resolution, possibility of absolute measurements of diffracted beam integral intensity and several orders higher sensitivity to weak structural distortions of highly perfect crystals in comparison with X-ray methods.
Although strictly mathematically the problem of dynamic X-ray diffraction at dislocational crystals is not yet solved, a number of models are developed, enabling to calculate dislocation concentration in crystals, well agreed with the experimental results.
Preliminary estimations have been made, and investigations have been carried out, showing perspectivity of gamma-ray diffractometry method for nondestructive dislocation concentration control in massive quartz crystals.
For high monochromatic gamma-ray generation isotopes of metals are used. These isotopes must be activated at regular intervals by thermal neutrons of nuclear reactor. That limits the possibility of employment of a gamma-ray diffractometer for investigations and control of crystals' perfection. Therefore it is necessary to study different materials for gamma-ray source, the spectral properties of radiation, methods of gamma-ray source activation and possibility of using of neutron generators and neutron tubes for source materials activation.
It is proposed in project:
1. investigations, finding and selection of optimum model for establishing correlation of diffractional gamma-ray radiation parameters with the dislocation concentration in real quartz crystals;
2. development of a method and programs of nondestructive dislocation concentration control in bulk crystal samples by means of gamma-ray diffractometer;
3. study of different materials for high monochromatic gamma-ray source and its spectral properties;
4. investigation of gamma-ray source activation methods and possibility of using of power neutron generators;
5. development and manufacturing of gamma-ray diffractometer intended for dislocation concentration control in quartz crystals.
The project development will be effected by specialists of three Institutions: STC "Poljus-1", VNIIA and PNPI connected with the development and production of weapons. The implementation of the project will give the following possibilities:
1. to develop and manufacture the gamma-ray diffractometer and method of non-destructive control of dislocation concentration in massive quartz crystals;
2. to improve the operating characteristics of gamma-ray diffractometer and to extend a field of it application when employing of a neutron generators for source material activation;
3. to choice dislocationless crystals for seed manufacturing and to sort "as grown" crystals per dislocation number in accordance with the customer's requirements and the normative documentation;
4. to elevate the yield during manufacture of products made of crystalline quartz;
5. to control quality of other types of bulk crystals: lithium niobate, lithium tantalate, langasite, lithium tetraborate, silicon, germanium etc;
6. to develop a neutron generator for application in activation analysis, neutron radiography, medicine, searching of explosive materials etc.
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