Positron Annihilation Rates in Lanthanum Hydrides

Abstract

Positron annihilation rates ${\ensuremath{\lambda}}_{1}$ and ${\ensuremath{\lambda}}_{2}$ 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${\mathrm{H}}_{2.7}$, ${\ensuremath{\lambda}}_{1}$ was approximately constant at 3.36 ${\mathrm{nsec}}^{\ensuremath{-}1}$. At higher compositions, ${\ensuremath{\lambda}}_{1}$ increased with increasing hydrogen content. A slower rate component ${\ensuremath{\lambda}}_{2}$ was observed for annihilation in lanthanum hydrides, but the associated intensity was very low. New data are also reported for lithium hydride as follows: ${\ensuremath{\lambda}}_{1}=3.12$ ${\mathrm{nsec}}^{\ensuremath{-}1}$, ${\ensuremath{\lambda}}_{2}=0.68$ ${\mathrm{nsec}}^{\ensuremath{-}1}$, and ${I}_{2}=6.30%$.