Precise line-shape analyses of Mössbauer spectra using the 58-keV transition in ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ have been made using an exact representation of the line shape in transmission. Spectra were made using a ${\mathrm{Dy}}_2$${\mathrm{O}}_3$ source at liquid-nitrogen temperature and absorbers of ${\mathrm{Tb}}_4$${\mathrm{O}}_7$ and ${\mathrm{TbAl}}_2$ at several temperatures from 81 to 297 K. We have measured the recoilless fraction as a function of temperature between 115 and 297 K for ${\mathrm{TbAl}}_2$ and at 81 and 294 K in ${\mathrm{Tb}}_4$${\mathrm{O}}_7$. 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. The mean lifetime of the first excited state of ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ was determined to be 77(1) ps. We have found the value of the interference parameter for this transition to be -0.0058(7), which appears larger in magnitude than predicted by theory.

• Received 19 September 1990

DOI:https://doi.org/10.1103/PhysRevB.43.7416