Nuclear Hyperfine Interaction inPr141

Nuclear hyperfine interactions in the 145-keV state of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ have been investigated by measurements on Mössbauer-scattered $\gamma$ rays. The magnetic moment of this level was determined to be ${2.78}_{-0.06\mathrm{}}^{+0.12\mathrm{}}{\mu }_N$, 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 ± 0.08 and 0.86 ± 0.06 MOe were obtained for the fields at 4.2°K in Pr${\mathrm{B}}_6$ and Pr${\mathrm{O}}_2$, respectively. Although these are only about ½ 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: $〈r_e^{}{}_{}{}^2〉-〈r_g^{}{}_{}{}^2〉=(6.3\mathrm{}\pm 2.5)\times {10}^{-3\mathrm{}}$ ${\mathrm{fm}}^2$.