Hazimu Kawamura

The Quadrupolar Effect in Alkali Halide Mixed Crystals

Using NaBr–NaCl mixed crystals, we have observed the quadrupolar effect on the nuclear resonance absorption line of Na. The minority halogen plays the role of “impurity” or “solute” as in the case of alloys treated by Bloembergen and Rowland. The satellites of Na in NaCl are affected when the solute Br comes at the third halogen site counted from Na site, where the field gradient then becomes q ∼10 21 cm -3 . From our analysis the antishielding factor λ for Na is given as ∼10. The asymmetric broadening of the central line due to the second order perturbation occurs when and only when the solute comes next to the Na nucleus. The specimen being a single crystal, the satellites of the second order arise at the definite positions depending upon the direction and strength of the external magnetic field. By measuring this shift of the resonance field, we see that the field gradients produced then at the Na site are nearly 1.4×10 23 cm -3 and 2.0×10 23 cm -3 , when Br - and Cl - are the solute ion, respectively....

Electron Spin Resonance of M centers in Potassium Chloride

An experiment on the electron spin resonance of colored KCl containing F and M centers was performed at 9500 Mc/sec. Subtracting the contribution from the F centers from the observed resonance curve, we could estimate the shape of the resonance line due to M centers alone, which was found to be Gaussian with the half-breadth of 48 oersteds and g value of 2,000. This result was discussed on the LCAO model.

The Statistical Time Lag of the Dielectric Breakdown of Mica, Glass and KCl

The statistical time lag of the dielectric breakdown were measured for mica, glass and KCl, applying the recurrent pulse voltage of 2×10 -8 ∼1×10 -7 sec width. For mica, the statistical time lag was as large as 10 -4 sec at 10% over-voltage. On the other hand, it was at most less than 10 -7 sec for glass and KCl at 10% over-voltage. Thus the “single avalanche mechanism” is favored for mica, since the occurrence of the extremely large avalanche which is responsible for the breakdown may rely on extreme fluctuation, and should be rare event at the threshold field. While, in the ease of KCl as well as glass, we may conclude that the “collective mechanism” is favored, from the fact that the statistical time lag is very short. From a rough estimation, we can conclude that the avalanche electrons become collective when their density becomes larger than 10 18 l/cm 3 .

NUCLEAR MAGNETIC RESONANCE OF Na

Measurements on two carefully prepared single crystals of NaCl indicate the previously observed Na/sup 23/ resonance line broadening is due in lattice imperfections. (D.E.B.)

sup 23

The dislocations act as a row of trapping centers. The rate of trapping W t is proportional to the dislocation density N d and carrier velocity v. Hence we have Here the constant of proportion w is considered to be the effective width of a dislocation for trapping, since it has the dimension of length.

IN SODIUM CHLORIDE CRYSTALS

In connection with his theory of the electric breakdown of amorphous substances, Frohlich suggested that in the glass state there should be various shallow electron traps below the conduction band, characteristic of the network structure of glass. On analizing our previous work on the electrical breakdown of glass, we arrived at the same inference concerning the existence of such shallow electron traps. Recently, Yokota has found that the glow curve of fused quartz colored by X-ray irradiation is more complicated than that of the crystal, and emphasized that this fact is intimately related to the unique properties of the glass structure.