The most prominent paramagnetic impurity center in single crystal alpha-quartz X-irradiated at room temperature is [AlO4]0, which contains an aluminum ion substituted for a silicon ion, with an electron removed from a neighboring oxygen by the ionizing radiation. A reinvestigation of this species at ca. 35 K using electron paramagnetic resonance has disclosed weak multiplets due to hyperfine interaction of the unpaired electron with an 17O nucleus, present in natural abundance (0.037%). The spin-Hamiltonian [Formula: see text] parameter matrix [Formula: see text] describing this interaction confirms the above model of [AlO4]0 and yields the coefficients [Formula: see text] and [Formula: see text] for the oxygen s- and p-orbitals, respectively, in the unpaired electron wavefunction ψ. Similarly, weak multiplets caused by 29Si (4.70% natural abundance) have been analyzed. The eigenvectors of [Formula: see text], in conjunction with eigenvectors of other parameter matrices (i.e., [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]), indicate that the trapping oxygen is one which would have a bond of the "long" type to the silicon replaced by aluminum (there are two different Si–O bond lengths in quartz). These eigenvectors also show that the axis of the oxygen p-orbital component of ψ is almost perpendicular to the Al–O–Si plane. The complete oxygen component of ψ has been used to obtain estimates of the dipolar contributions to [Formula: see text] and [Formula: see text], which however do not agree too well with the respective observed anisotropic components.

The correct positions of the deuterium (D) atoms of many of the bound waters in the protein concanavalin A are revealed by neutron Laue diffraction. The approach includes cases where these water D atoms show enough mobility to render them invisible even to ultra-high resolution synchrotronradiation X-ray crystallography. The positions of the bound water H atoms calculated on the basis of chemical and energetic considerations are often incorrect. The D-atom positions for the water molecules in the Mn-, Ca-and sugarbinding sites of concanavalin A are described in detail.

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The centers [AlO4/M+]+, formed in α-quartz by X-irradiation at 77 K, contain an aluminum ion substituted for a silicon ion, with an electron removed from a neighboring oxygen by the ionizing radiation. In addition, there is an interstitial ion M+ which acted as a charge compensator before the irradiation. Centers [AlO4/H+]+ and [AlO4/Li+]+ have been re-examined by EPR (at ca. 35 K), including measurement of small hyperfine splittings due to the compensator ions. The spin-Hamiltonian parameter matrices (i.e., [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]) show that the hole-trapping oxygen in these species is linked via a "short" bond to aluminum (there are two different Si–O bond lengths in quartz). The probable positions of the compensating ions (Li+, H+) in a channel parallel to the crystallographic c-axis are reported.

The temperature dependence of the luminescence from activators in BaFBr : EuZt photostimulated between 10 and 300 Kin the optical absorptions of F centres produced by room temperature x-irradiation, revealed two thermally-activated processes. The photostimulated luminescence (PSL) increases sharply inintensity when excited between 60 and 100 K. After the low-temperature PSL is exhausted by continuous F centre excitation, it can be almost entirely regained by warming the crystal to 300 K. This thermal cycle can be repeated several times. It is shown by EPR that no Eu3+ is formed upon x-irradiation at 300 K. These results are explained with a model for the PSL mechanism which involves a loose aggregate of E d t , F, and hole centres.

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