Positron Annihilation Rates in Lanthanum Hydrides

Positron annihilation rates ${\lambda }_1$ and ${\lambda }_2$ are reported for a series of lanthanum hydride samples of compositions from La${\mathrm{H}}_{2.0}$ to La${\mathrm{H}}_{2.9}$. From La${\mathrm{H}}_{2.0}$ to La${\mathrm{H}}_{2.7}$, ${\lambda }_1$ was approximately constant at 3.36 ${\mathrm{nsec}}^{-1\mathrm{}}$. At higher compositions, ${\lambda }_1$ increased with increasing hydrogen content. A slower rate component ${\lambda }_2$ was observed for annihilation in lanthanum hydrides, but the associated intensity was very low. New data are also reported for lithium hydride as follows: ${\lambda }_1=3.12\mathrm{}$ ${\mathrm{nsec}}^{-1\mathrm{}}$, ${\lambda }_2=0.68\mathrm{}$ ${\mathrm{nsec}}^{-1\mathrm{}}$, and $I_2=6.30\%$.