Mössbauer Scattering: The Quadrupole Interaction in Osmium Metal

The Mössbauer scattering of the 137-keV gamma radiation from the first 2+ state of ${\mathrm{Os}}^{186}$ is reported. The effect, i.e., the Mössbauer intensity-to-background ratio at zero relative velocity between source and scatterer, is, at 15°K, approximately 3:1. The full width at half-maximum of the velocity spectrum is 1.36±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°K. The average value of ${\Theta }_D$, assuming it to be the same for source and scatterer, is 375±20°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, ${\omega }_E=(35.6\mathrm{}\pm 3.3)\times {10}^6/sec$. From the $B\left(E2\mathrm{}\right)\mathrm{}$ value of the transition, the value the EFG of hexagonal close-packed (hcp) osmium is deduced to be $q=(3.50\mathrm{}\pm 0.50)\times {10}^{17}$ 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.