Nuclear Alignment of Ce137m, Ce137, Ce139, Ce141, and Ce143

Abstract

Nuclei of ${\mathrm{Ce}}^{137m}$, ${\mathrm{Ce}}^{137}$, ${\mathrm{Ce}}^{139}$, ${\mathrm{Ce}}^{141}$, and ${\mathrm{Ce}}^{143}$ were aligned at low temperatures by the magnetic hyperfine-structure method. The angular distributions and the plane polarization of the emitted gamma radiation were measured as functions of temperature. For the spin sequence $\left({\mathrm{Ce}}^{137m}\right)\frac{11}{2}(M4,E5,255\mathrm{} \mathrm{keV})\frac{3}{2}\left({\mathrm{Ce}}^{137}\right)$, the mixing ratio, $\left|\delta \right(\frac{E5\mathrm{}}{M4\mathrm{}}\left)\right|$, is less than 0.7. For the sequence $\left({\mathrm{Ce}}^{137}\right)\frac{3}{2}(i_{\beta }=0,1)\frac{3}{2}(M1,E2,445\mathrm{} \mathrm{keV})\frac{5}{2}$, the magnetic moment of ${\mathrm{Ce}}^{137}$ is $\left|{\mu }_N\right|=0.90\mathrm{}\pm 0.15$ nm and $-2.6<\delta \left(\frac{E2\mathrm{}}{M1\mathrm{}}\right)<-0.17\mathrm{}$. The spin of the 455-keV level of ${\mathrm{La}}^{137}$ is shown to be $\frac{3}{2}$. For the sequence $\left({\mathrm{Ce}}^{139}\right)\frac{3}{2}(i_{\beta }=1)\frac{5}{2}(M1,E2,166\mathrm{} \mathrm{keV})\frac{7}{2}\left({\mathrm{La}}^{139}\right)$, the magnetic moment of ${\mathrm{Ce}}^{139}$ is $\left|{\mu }_N\right|=0.95\mathrm{}\pm 0.20$ nm and $\delta \left(\frac{E2\mathrm{}}{M1\mathrm{}}\right)=+0.034\mathrm{}\pm 0.034$. The 166-keV level of ${\mathrm{La}}^{139}$ has spin $\frac{5}{2}$. For the sequence $\left({\mathrm{Ce}}^{141}\right)\frac{7}{2}(i_{\beta }=0)\frac{7}{2}(M1,E2,142\mathrm{} \mathrm{keV})\frac{5}{2}\left({\mathrm{Pr}}^{141}\right)$, the magnetic moment of ${\mathrm{Ce}}^{141}$ is ${\mu }_N=1.30\mathrm{}\pm 0.20$ nm and $\delta \left(\frac{E2\mathrm{}}{M1\mathrm{}}\right)=+0.066\mathrm{}\pm 0.022$. The spin of the 142-keV level of ${\mathrm{Pr}}^{141}$ is established as $\frac{7}{2}$. The beta transition is predominantly $i_{\beta }=0\mathrm{}$. For the sequence $\frac{7}{2}\left({\mathrm{Ce}}^{143}\right)(i_{\beta }=0,1)\frac{5}{2}\left(\frac{7}{2}\right)(M1,E2,294\mathrm{} \mathrm{keV})\frac{5}{2}\left(\frac{7}{2}\right)$, the magnetic moment of ${\mathrm{Ce}}^{143}$ is $\left|{\mu }_N\right|=1.0\mathrm{}\pm 0.3$ nm, and $\delta \left(\frac{E2\mathrm{}}{M1\mathrm{}}\right)=-0.80\mathrm{}\pm 0.20$. The magnetic moments were found to be in agreement with configuration-mixing calculations. Evidence was found for two kinds of orientation attenuation in cerium magnesium nitrate.