E.P.R. Study of Nuclear Radiation Effects in CaWO₄

Abstract

Since the discovery of its usefulness as a laser host crystal [1], calcium tungstate containing ions that are paramagnetic in the ground state has been the subject of EPR investigation in many laboratories. The examples are the transition elements, particularly the rare earths [2,3] such as Ce and Nd, the iron-group elements such as Cr, Mn and Fe, and Y [4–7]. In comparison however, the metastable EPR centers in CaWO₄ have been less well investigated, despite the fact that a variety of paramagnetic centers can be produced by exposure to nuclear radiation. At the time our investigations were begun, the only publication was that by Zeldes and Livingston [8], who had reported high- and low-field paramagnetic W⁵⁺ centers produced by gamma irradiation. Consequently it seemed to us that a systematic study of the EPR centers produced by neutrons and gamma rays might provide some understanding of impurity sites, impurity interactions, and defect structures in CaWO₄.

Supported in part by a grant from the National Aeronautics and Space Administration.