Portal de Periódicos da CAPES

Expansion of Potassium and Sodium Chloride Crystals Due to X-Ray Irradiation of Weak Intensities

1956; American Institute of Physics; Volume: 102; Issue: 4 Linguagem: Inglês

10.1103/physrev.102.968

1536-6065

Lanying Lin,

Terahertz technology and applications

Rectangular cleaved samples of potassium and sodium chloride crystals having dimensions of about 12\ifmmode\times\else\texttimes\fi{}10\ifmmode\times\else\texttimes\fi{}1.5 mm were irradiated for times up to three hours with x-rays (48 kv at 18 ma) from a molybdenum target tube passing through a beryllium window at room temperature in air and in helium atmospheres. The crystals were placed in a thermostatted enclosure regulated to within 0.01\ifmmode^\circ\else\textdegree\fi{}C. The crystals were about 2\textonequarter{} in. from the x-ray tube beryllium window. The change in length of the largest dimension of the crystal was measured during and after the irradiation by a capacitance-type dilatometer with a sensitivity of ${10}^{\ensuremath{-}8}$ cm. A series of measurements were carried out employing different times of irradiation and it was found that the relation between the relative linear expansion of the crystal and the optically determined average concentration of $F$-centers was linear with a constant of proportionality remarkably close to the value of $\frac{{d}^{3}}{12}$, where $d$ is the lattice constant of the crystal. There was a time delay of about 20-30 minutes before the expansion could be detected. This time delay was increased by plastic deformation. The results did not depend on the fraction of the crystal volume which was irradiated. The rate of formation of a certain $F$-center concentration in the irradiated portion of the crystal was directly proportional to the fraction of the volume exposed to the irradiation. In partially irradiated crystals, the rate of formation of $F$-centers in the nonirradiated portion upon subsequent irradiation was greatly increased by the presence of the adjacent irradiated part. The merits of possible models to explain these results are discussed.