Slowing down of 3-eV Sm ions in Eu compounds.

Abstract

Slowing down of ions at ultralow velocities has been studied in the case of 0.02-eV/amu $^{152}\mathrm{Sm}$ recoils in ${\mathrm{EuF}}_{2}$, ${\mathrm{EuF}}_{3}$, ${\mathrm{EuCl}}_{3}$, and ${\mathrm{Eu}}_{2}$${\mathrm{O}}_{3}$. The recoiling atoms were produced in \ensuremath{\beta} decay of $^{152}\mathrm{Eu}$. The Doppler-broadened 842- and 963-keV \ensuremath{\gamma}-rays emitted by the recoiling $^{152}\mathrm{Sm}$ nuclei were detected by a crystal spectrometer. The experimental \ensuremath{\gamma}-ray line shapes were simulated by molecular-dynamics technique using empirically derived interatomic pair potentials. The lifetime of 28\ifmmode\pm\else\textpm\fi{}6 fs was deduced for the first excited state at 963 keV in $^{152}\mathrm{Sm}$.