Mössbauer Scattering: The Quadrupole Interaction in Osmium Metal

Abstract

The M\ossbauer scattering of the 137-keV gamma radiation from the first 2+ state of ${\mathrm{Os}}^{186}$ is reported. The effect, i.e., the M\ossbauer intensity-to-background ratio at zero relative velocity between source and scatterer, is, at 15\ifmmode^\circ\else\textdegree\fi{}K, approximately 3:1. The full width at half-maximum of the velocity spectrum is 1.36\ifmmode\pm\else\textpm\fi{}0.07 times that theoretically expected. The Debye temperature of the osmium scatterer was determined and appears to increase with increasing temperature, from 4.2 to 80\ifmmode^\circ\else\textdegree\fi{}K. The average value of ${\ensuremath{\Theta}}_{D}$, assuming it to be the same for source and scatterer, is 375\ifmmode\pm\else\textpm\fi{}20\ifmmode^\circ\else\textdegree\fi{}K. The angular distribution of the scattered radiation was measured using a three-detector geometry. Assuming that the attenuation of the correlation is due to an axially symmetric electric field gradient (EFG) acting on the quadrupole moment of the 2+ state, we obtain for the quadrupole interaction, ${\ensuremath{\omega}}_{E}=(35.6\ifmmode\pm\else\textpm\fi{}3.3)\ifmmode\times\else\texttimes\fi{}{10}^{6}/sec$. From the $B(E2)$ value of the transition, the value the EFG of hexagonal close-packed (hcp) osmium is deduced to be $q=(3.50\ifmmode\pm\else\textpm\fi{}0.50)\ifmmode\times\else\texttimes\fi{}{10}^{17}$ V/${\mathrm{cm}}^{2}$. By comparing this value with the lattice contribution to the EFG as well as to the known EFG of hcp rhenium metal, we conclude that the conduction-electron contribution is significant and probably changes substantially from rhenium to osmium.