Moessbauer studies in tungsten, iridium, and terbium using line shape analysis
Abstract
Precise Mossbauer line shape analyses have been carried out in tungsten and iridium metal and in compounds of terbium, using an exact representation of the line shape in transmission. By using exceptionally intense sources ($\sim$70 Ci for $\sp{183}$Ta), and carefully chosen constraints between sets of Mossbauer effect (ME) spectra, we have been able to make a quantitative test of the theory of final state effects. We have also determined the temperature dependence of the recoilless fraction, f(T), for $\sp{183}$W in tungsten metal to about 1% accuracy, which is an order of magnitude better than previous Mossbauer or x-ray investigations, between 80 K and 1067 K. The Debye model fits our results from 80 K through 968 K, with a Debye Mossbauer temperature of 336.5 K, when a correction for thermal expansion is included. We also measured f(T) between 115 K and 297 K for TbAl$\sb2$, and at 81 K and 294 K in Tb$\sb4$O$\sb7$. If the theoretical value of the internal conversion coefficient of 11 is accepted, we cannot fit our results to a Debye model, even in a rough approximation. We have used the recoilless fraction data to derive a value of 8.76(10) for the internal conversion coefficient for the 46.5 keV transition in $\sp{183}$W, with a novel approach based on the quasiharmonic approximation to the lattice vibrations, which determines the temperature dependence of the recoilless fraction. The mean lifetimes for the ME iridium and tungsten cases studied were found to be 133(4) and 265(1) ps, respectively, while the mean lifetime of the first excited state of $\sp{159}$Tb was determined to be 77(1) ps. The interference parameters, times one hundred, that we find in this investigation of $\sp{183}$W in tungsten metal (46.5 keV), $\sp{191}$Ir in iridium metal (129 keV), and $\sp{159}$Tb in TbAl$\sb2$ (58 keV) are -0.317(6), -0.77(10), and -0.58(7), respectively. These values are all greater in magnitude than the theoretically calculated values by about 10 to 30%, although the $\sp{191}$Ir case is within our present errors. The other two cases appear to differ with theory, and indicate that the theoretical calculations need refinement if they are to be used in studies of time reversal invariance.
Degree
Ph.D.
Advisors
Mullen, Purdue University.
Subject Area
Condensation|Nuclear physics|Radiation
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