Study of positron lifetimes in α, β and γ cerium at high pressures

The positron lifetimes in the α, β and γ phases of Ce have been measured by applying hydrostatic pressure (up to 1.4 GPa) and by reducing the temperature (to 80 K). Two-component fitting programs showed that the main component ( ≈ 90%) had virtually the same mean lifetime ( ≈ 233 ps) in all three phases. The uncertainty in each lifetime was ±2 ps. With this high precision, our results are in agreement with those of band calculations which give the same number of 4f electrons ( ≈ 1.2) in all phases.