MOSSBAUER LINE-SHAPE PARAMETERS FOR W-183 AND IR-191 IN METALLIC TUNGSTEN AND IRIDIUM

We have carried out precise Mossbauer line-shape analyses in tungsten and iridium metal using an exact representation of the line shape in transmission. By using exceptionally intense sources (approximately 70 Ci for Ta-183) and carefully chosen constraints between sets of Mossbauer-effect spectra, we have been able to make a quantitative test of the theory of final-state effects. The temperature dependence of the recoilless fraction, f(a)(T), for W-183 in tungsten metal has been determined to about 1% accuracy, which is an order of magnitude better than previous Mossbauer or x-ray investigations, between 80 and 1067 K. The Debye model fits our results from 80 through 968 K, with a Debye Mossbauer temperature of 336.5 K, when a correction for thermal expansion is included. The recoilless fraction data were used to derive a value of 8.76(10) for the internal conversion coefficient for the 46.5-keV transition in W-183, with an approach based on the quasiharmonic approximation to the lattice vibrations, which determines the temperature dependence of the recoilless fraction. The interference parameters, times 100, that we find in this investigation of W-183 in tungsten metal (46.5 keV) and Ir-191 in iridium metal (129 keV), are -0.317(6) and -0.77(10), respectively. These values are both greater in magnitude than the theoretically calculated values by about 10%, although the Ir-191 case has errors large enough that the comparison with theory is inconclusive. These results differ with theory, and would indicate that the theoretical calculations of interference need refinement if they are to be used in studies of time-reversal invariance.