Nuclear Hyperfine Interaction inPr141

Abstract

Nuclear hyperfine interactions in the 145-keV state of $^{141}\mathrm{Pr}$ have been investigated by measurements on M\"ossbauer-scattered $\ensuremath{\gamma}$ rays. The magnetic moment of this level was determined to be ${2.78}_{\ensuremath{-}0.06}^{+0.12}{\ensuremath{\mu}}_{N}$, a value which is considerably larger than that predicted by Kisslinger and Sorensen. Renormalizing ${g}_{l}$ in their calculation to account for meson-exchange effects reduces the disagreement significantly. The magnetic field at the site of the Pr nucleus has been investigated for a number of compounds. The values 2.07 \ifmmode\pm\else\textpm\fi{} 0.08 and 0.86 \ifmmode\pm\else\textpm\fi{} 0.06 MOe were obtained for the fields at 4.2\ifmmode^\circ\else\textdegree\fi{}K in Pr${\mathrm{B}}_{6}$ and Pr${\mathrm{O}}_{2}$, respectively. Although these are only about \textonehalf{} the values expected for the internal fields in the corresponding free Pr ions, the temperature dependence closely followed a Brillouin function. Line broadening that persisted to temperatures well above the magnetic-ordering temperatures was observed for these compounds indicating the presence of a smaller residual hyperfine interaction. Isomer shifts have been observed for a number of Pr compounds. Based on isomer shifts between ionic trivalent and tetravalent compounds, the difference in the mean square charge radii of the excited and ground states is estimated: $〈r_{e}^{}{}_{}{}^{2}〉\ensuremath{-}〈r_{g}^{}{}_{}{}^{2}〉=(6.3\ifmmode\pm\else\textpm\fi{}2.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ ${\mathrm{fm}}^{2}$.