POSITRON ANNIHILATION IN GAMMA- AND ALPHA-CERIUM

The γ→α phase transition of cerium has been investigated by measurement of the positron lifetime and angular correlation of positron-annihilation radiation in the two phases. The lifetime in the α phase was observed to be 8% shorter than the lifetime in the γ phase when the α phase was produced by the application of pressure; and it was observed to be 5% longer when the α phase was produced by lowering the temperature. The angular correlation from α-cerium produced by pressure was observed to be slightly broader than that from γ-cerium, in contrast to the narrowing previously observed when α-cerium was produced by lowering the temperature. Since the observed changes are much smaller than predicted by models which explain the γ→α transition by assuming a transfer, or partial transfer, of the 4f electron to the conduction band, it is concluded that such electronic promotion does not occur. © 1969 The American Physical Society.