KINETICS OF THE ACCUMULATION OF STORED ENERGY AS A FUNCTION OF IRRADIATION DOSE IN SINGLE CRYSTALS OF THE KCl—KBr SYSTEM

E. M. Golovchanskii

(Presented by the scientific seminar of the Laboratory of Dielectrics and Semiconductors)

At present, one of the most important problems in solid-state physics is the establishment of the basic regularities governing the action of radiation on materials. Under the action of irradiation, various kinds of defects arise in solids, leading to changes in the properties of the material. The formation of defects in the lattice is associated with an expenditure of energy; therefore an irradiated material possesses additional potential energy (stored energy). Thus, the change in all the properties of a solid as a result of irradiation must be closely connected with the magnitude of the stored energy. Knowledge of the laws of accumulation of stored energy under irradiation, and of its magnitude, is of great interest for investigating the influence of irradiation on a solid. A number of works [1÷4] have been carried out to determine the magnitude of stored energy under irradiation for single crystals of alkali-halide salts. We know of no works on determining the magnitude of stored energy under irradiation for single crystals of solid solutions of alkali-halide salts.

Fig. 1. Curve of accumulation of the magnitude of stored energy as a function of the dose of proton irradiation in single crystals of a solid solution of the KCl—KBr system.

From a single crystal of the KCl—KBr system (64% KCl, KCl—chemically pure grade, KBr—pure grade), grown from the melt in the crystallization laboratory of the Tomsk Polytechnic Institute, samples were rolled out—

of \(6 \times 6\ \text{mm}^2\), with a thickness from 0.47 to 0.52 mm; their weight was in the range \((36 \div 46) \times 10^{-3}\) g. The specimens were prepared in pairs so that one specimen was the mirror image of the other. The masses of the specimens in each pair differed by no more than \((1 \div 2) \times 10^{-5}\) g, and their surface areas by no more than 1%.

The crystals were irradiated in a cyclotron with protons of energy 4.0 MeV. Irradiation in a cyclotron makes it possible: (a) to obtain sufficient uniformity of defects throughout the volume of the crystal; (b) to vary the irradiation intensity over a wide range. Under proton irradiation it is easy to calculate the energy absorbed by the specimen. The crystals were irradiated from two sides in aluminum foil 10 microns thick at room temperature, at an intensity of \(1.5 \times 10^{14}\) protons/\(\text{cm}^2\cdot\text{h}\). The stored energy was determined by the dissolution method [2].

The calorimeter made it possible to measure stored energy from 0.09 cal/g and above. The accuracy of the method was 5%. Figure 1 shows the curve for the accumulation of the stored-energy value in a single crystal of the KCl—KBr system as a function of irradiation dose. The kinetic curve of stored energy has two clearly expressed stages. There is a rapid increase at the beginning of irradiation up to \(1.5 \times 10^{14}\) pr/\(\text{cm}^2\), and a slow, almost linear increase upon further irradiation up to \(5.3 \times 10^{14}\) pr/\(\text{cm}^2\). The maximum value of the stored energy at an integral flux of \(5.3 \times 10^{14}\) pr/\(\text{cm}^2\) is 0.96 J/g.

LITERATURE

1. K. Kobayashi. Phys. Rev. 102, 348, 1956.
2. A. V. Kuzmina, V. A. Holler. The Effect of Radiation on the Properties of Materials (Conference Proceedings), Novosibirsk, 1963.
3. Phelps, Phys. Rev. 128, No. 4, 1962.
4. Hennen, N. Z. and Phys. 15, No. 1, 1963.