ATTENUATION COEFFICIENTS OF β-RADIATION IN SOLID SOLUTIONS OF SINGLE CRYSTALS AND PRESSED SALT SAMPLES, KCl—KBr

S. L. Kashchuk, V. A. Popov

It is known that electron fluxes, passing through a solid, undergo scattering by atoms and electrons. In addition, electron fluxes are reflected and scattered at boundaries. It is of interest to consider the question of electron scattering by the inhomogeneities inherent in solid solutions of alkali-halide compounds taken in the form of single crystals and pressed samples. In this work we attempted to determine the possibility of studying disturbances of the structure of a solid solution by measuring the attenuation coefficients of electrons of different energies in single crystals and pressed samples. The present communication gives the results of measurements of the attenuation coefficients of β-rays from a Tl—204 source.

When electrons pass through a substance, fast electrons lose energy in the substance mainly through ionization processes and bremsstrahlung processes, in which scattering of particles in the field of the nucleus leads to the emission of radiation quanta (radiative losses) [1, 2].

Radiative losses are important at electron velocities close to the velocity of light, i.e., at electron energies of several \(M_{\text{eV}}\) [2]. Consequently, under the conditions of our experiment, at electron energies on the order of \(1\,M_{\text{eV}}\), ionization is the most important type of interaction of electrons with matter. The rate of electron energy loss in passing through matter can be represented by the equation

\[ dE = c\rho z \frac{N}{A}\,dx, \tag{1} \]

where \(\rho\) is the density of the substance, \(z\) is the nuclear charge, \(N\) is Avogadro’s number, and \(A\) is the atomic weight. The quantity \(\frac{z}{A}\), approximately constant for all elements, varies from 0.5 to 0.4. Consequently, the energy losses due to ionization are \(dE \sim \rho \cdot dx\) (2), i.e., the energy losses are proportional to the density of the material under study and to the thickness of the sample, i.e., to the areal density of the substance, g/cm\(^2\).

Preparation of samples

Single crystals of KCl–KBr solid solutions were grown by the Kyropoulos method. Samples measuring \(10 \times 10\) mm and \(0.3\)–\(1.0\) mm thick were cleaved. The composition of the samples was analyzed from the position of the \(F\)-band.

Pressed samples were prepared from powders of salts of various compositions of the solid solution. The powders were sieved through kapron sieve No. 100. To obtain samples of different thicknesses, powder portions from 160 mg to 350 mg were prepared. The portions were dried in the pressing mold at a temperature of \(130^\circ\mathrm{C}\) for 20–35 min (depending on the size of the portion). The samples were pressed in a metal pressing mold at a temperature of \(140^\circ\mathrm{C}\) for 60 min under a pressure of \(30\ \mathrm{kg}/\mathrm{cm}^2\).

The samples were obtained in the form of transparent pellets, \(0.45\) to \(0.9\) mm thick, pressed into metal rings.

The density of the pressed samples was measured by weighing and by the method of filling the open pores of the sample with benzene. The density obtained for the pressed specimens was 99% of the density of the single crystals. The chemical composition of the samples was determined by titration.

Measurement method

The method for measuring the attenuation coefficient of \(\beta\)-radiation was described previously [3]. A \(T^{204}\) preparation with \(E_e = 0.766\) MeV served as the source of \(\beta\)-rays. The accuracy of measuring the attenuation coefficients was of the order of 2%.

Measurement results

The results of measuring the attenuation coefficients of \(\beta\)-radiation in single crystals of KCl–KBr solid solutions and in pressed KCl–KBr salt samples are presented in Table 1 and in Fig. 1.

Fig. 1. Dependence of the mass attenuation coefficient of \(\beta\)-radiation on the chemical composition of KCl–KBr solid solutions.
\(\cdots\) for single crystals,
\(\times\times\times\) for pressed samples.

From Fig. 1 it is seen that, in the present case, the attenuation coefficients of \(\beta\)-radiation do not depend on the structure of the samples and are completely op-

are determined by the electron density of the substance. The higher the electron density, the larger the attenuation coefficient of β-radiation of a given energy.

Table 1

The attenuation coefficients of β-radiation for solid solutions of single crystals and pressed specimens of KCl—KBr salts depend additively on the chemical composition.

REFERENCES

1. R. G. Flüerthy. In: Chemical Action of High-Energy Radiation. IL Publishing House, 1949.
2. Handbook of Nuclear Physics. Moscow, State Publishing House of Technical-Theoretical Literature, 1963.
3. S. L. Kashuk. In: The Effect of Radiation on Materials. Novosibirsk, 1963.