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The nuclear quadrupole resonance frequencies of 75As in the α and β forms of As4S3 have been measured at 77, 195, and 293 K. The frequencies at 77 K were: α phase 64.87 65.94 79.56 MHz β phase 65.42 67.16 79.65 MHz An analysis is presented in terms of Townes-Dailey theory and of the temperature dependence in terms of Bayer-Brown theory. The differences in frequencies of the α and β forms were attributed to the effect of electrostatic field gradients, estimated by lattice sums. Allowance must be made for the thermal expansion of the lattice to obtain a consistent interpretation.

The oxidation states of 32P species recoiling from the 35Cl(n,ar)32P reaction in KCl lattices have been studied as a function of the gamma doses received by the crystal prior to and during neutron irradiation, and as a function of thermal annealing at various temperatures. In addition to the oxidative thermal annealing processes usually found for recoils from nuclear reactions in solids, reducing reactions can occur, and seem to have a complex temperature dependence. Gamma irradiation prior to neutron bombardment provides a reducing environment in the crystal, although this effect tends to be destroyed at higher doses. Evidence is presented to suggest that F-centres may be the agents responsible for the reducing reactions.Most studies of the chemical behaviour of atoms recoiling from nuclear reactions in inorganic solids have been concerned with activation of the central atom in oxyanions. Various post-irradiation treatments influence the proportion of the radiospecies which is found in the form of the parent anion when the target is dissolved in aqueous solutions. In such post-irradiation annealing behaviour, activated exchange reactions,la 2 or recombinations of the fragments from anion disruption with oxygen atoms 3 could have occurred, although in principle reaction of charged radio-atoms with positive holes or electron donating centres could also have taken place.We have selected KCl crystals as targets because this system is chemically simpler than the oxy-anions and exchange reactions cannot occur since the 32P is non-isotopic with the lattice constituents. In addition, the several valency states of 32P should allow oxidation-reduction reactions in the solid to be studied, while the considerable body of knowledge of radiation-induced lattice defects in the alkali halides should permit some defect-recoil interactions to be examined.Carlson and Koski had shown that oxidation of 32P recoils can take place in KC1 crystals when they are subjected to thermal or radiation annealing after neutron bombardment,4 while Sue and Caillat demonstrated an increase in lower-valency 32P when pile-irradiated NaCl monocrystals were heated to 350°C for a few minutes.5 EXPERIMENTAL MATERIALS.-A.R. KCI was recrystallized once from aqueous solution, and then dried by pumping to ca. 50p Hg and sealing off with P2Q5 for 24 h.mRADIATIoN.-Gamma irradiations were done at room temperature in the Harwell Spent Fuel Radiation Assembly, with a dose accuracy of A5 %. Neutron irradiations were done