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Measurements have been made of the anisotropy of the optical absorption induced by neutron and electron irradiation. Some of the measurements were made with a six-plate fluorite polarizer, whose efficiency was found to be 65% at 2500 å, and which could be used at shorter wavelengths than a Clan-Thomson prism.In the spectrum induced by neutron irradiation, bands are resolved at -185°c at 1.9, 2.2, 2.8, 3.5, 4.1, 4.8 and 6.1 ev, the latter being measured both with a quartz spectrophotometer and a fluorite vacuum spectrograph. The 6.1 ev band was found to be isotropic but the 2.8, 3.5, 4.1 and 4.8 ev bands were anisotropic, having parallel to perpendicular ratios greater than 1. The anisotropy measurements reveal the presence of a band of opposite anisotropy at 5.3 ev. In order to account for the complete shape of the spectrum of the anisotropic ratio it is necessary to assume tho presence of other bands having the same anisotropy as the 5.3 ov band. Tho 5.3 ev band did not appear in the electron irradiated specimens, although both the 4.8 (μ∥ < μ⊥ and 6.1 ev (isotropic) bands were found. Possible models for these two centres are discussed.The rate of decrease of absorption with heat treatment haa been measured for temperatures up to 500°c and is compared with the rate of recovery of the neutron induced expansion studied by Martin (1959).

The variation of the absorption strength and spectrum in the region of 3 μ has been determined for different specimens of crystalline quartz and for x-ray, electron and pile irradiated crystals. It is shown that the 3 μ group of bands is associated with imperfections rather than harmonics or combinations of lattice vibration frequencies, and that the imperfections are not Frenkel or Schottky defects. Two of the bands, 2·88 and 2·95 μ, are anisotropic, having anisotropic absorption ratios (E∥c/E⊥C)≤0·130 and ≤0·145 respectively. A band is induced by pile irradiation at 2·79 μ but tends to saturate at a low dose (< 1019n® cm×2). The band is not produced by ionizing radiation. It is suggested that the 2·79 μ band may be due to 0-H bond formation by association of hydrogen impurity with the products of atomic damage. This band is also anisotropic with a ratio of 0·71. Possible defect axis directions which could give the observed anisotropic ratios are discussed.

SOME experiments with gas discharges in pure iodine, pure mercury and mercury-rare gas mixtures have led to the discovery of four new optical maser transitions in the near infra-red.