No abstract

An evaluation of the consistency between the absolute voltage determination of the threshold energy of the Li 7 (/>,»)Be 7 reaction as measured by Herb, Snowdon, and Sala and earlier independent absolute alphaparticle energy measurements has been made. The experimental comparison was affected by employing the natural alpha-particles from polonium and radium C, the energy of which has been measured absolutely by several authors using magnetic deflection methods. In this experiment the alpha-particles from these substances have been electrostatically deflected in the 90° cylindrical electrostatic analyzer at the University of Wisconsin. Alpha-particle line measurements were analyzed by numerical integration of resolution and source functions and in themselves contributed negligibly to the uncertainties of the comparison. The resulting alpha-particle energies, evaluated by comparison with the energy of the Li 7 (^,«)Be 7 threshold, agree with earlier measurements, and indicate that within the limits of accuracy of the experiments, all determinations give identical results.

LETTERS TO THE EDITOR 603 be expected from the uncertainties in both the theory and the experiment.Work has been done on a number of other materials including MnO, Cr 2 0 3 , and ZnFe 2 0 4 and is being continued with a view to studying the dependence of the energy distribution on the temperature, the angle of scattering, and the degree of magnetic order. An account of this work will be submitted to the Canadian Journal of Physics. Energy distributions of neutrons scattered by vanadium metal under several different conditions have been measured by the author with results in agreement with the theory. This work is being continued with a view to obtaining the frequency distribution of the normal modes in vanadium metal.

The lattice expansion in neutron-irradiated LiF was investigated in order to establish either Frenkel or Schottky defects as the cause of the expansion. For uniformly irradiated crystals, it was shown that x-ray lattice parameter and density changes are equivalent to within 6 percent. It follows that Schottky defects cannot account for more than 6 percent of the expansion and that Frenkel defects are predominant. The annealing of a nonuniformly irradiated crystal indicates a recovery process of order higher than one.

Measurements are reported of the magnetic susceptibility of neutron irradiated quartz. as a function of irradiation time. The results are interpreted in terms of the density of centers produced by the irradiation and are compared with optical and x-ray studies of neutron damaged quartz..