Mössbauer Effect Following Coulomb Excitation of the 43.8-keV State ofDy161

The Mössbauer effect following Coulomb excitation of the 43.8-keV state of ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ was studied for several Dy compounds and Dy metal. At 85°K, using 3.3-MeV $\alpha$ particles, effects as large as 3.5% were observed; a scintillation counter gave typical counting rates of 2000 counts/sec; 43.8-keV $\gamma$ rays made up about one third of the total count rate. The half-life of this state predicts $2{\Gamma }_0=8\mathrm{}$ mm/sec; the narrowest single line observed was 16 mm/sec. Dy-metal spectra taken at various temperatures were interpreted assuming a normal hyperfine interaction plus a central peak due to relaxation effects. The extracted value of the nuclear magnetic-dipole moment for this level of $(-0.134\mathrm{}\pm 0.005){\mu }_N$ agrees with the value calculated using the Nilsson model. The extracted value of the ratio of the intrinsic quadrupole moments of the ground and excited states of 1.12 ± 0.27 agrees with the value of 1.0 predicted by the Nilsson model. The extracted difference in the nuclear radius for the ground and excited states is $\frac{\delta R}{R}=(-1.2\mathrm{}\pm 0.6)\times {10}^{-5\mathrm{}}$. A radiation-damage induced isomer shift corresponding to ${\mathrm{Dy}}^{4+}$ was observed in the Dy${\mathrm{F}}_3$ target at liquid-nitrogen temperature.