Mössbauer Scattering inPr59141

We have completed a series of Mössbauer scattering experiments on ${}_{59}{}^{141}{}_{}{}^{}\mathrm{Pr}$ using an axially symmetric backscattering arrangement. From the relative isomer shifts between ${\mathrm{Pr}}^{+4\mathrm{}}$ and ${\mathrm{Pr}}^{+3\mathrm{}}$ compounds we estimate that the change in the mean-square charge radius between the 145-keV excited state and ground state of the ${}_{59}{}^{141}{}_{}{}^{}\mathrm{Pr}$ nucleus is 1.28 × ${10}^{-28\mathrm{}}$ ${\mathrm{cm}}^2$. Pr${\mathrm{O}}_2$ exhibits ordered magnetic behavior below 15 K. We estimated the hyperfine fields for the electronic ground states of a ${\mathrm{Pr}}^{+4\mathrm{}}$ ion in a magnetic cubic crystal and compared the observed values of the effective fields with the calculated fields. We found the best agreement when we assumed that the exchange field was directed toward a nearest-neighbor ${\mathrm{Pr}}^{+4\mathrm{}}$ ion. We obtained $(3.1\mathrm{}\pm 0.2){\mu }_N$ for the magnetic moment of the 145-keV spin-$\frac{7}{2}$ level of ${}_{59}{}^{141}{}_{}{}^{}\mathrm{Pr}$.