Quadrupole Moment of the 21.6-keV State ofEu151

Mössbauer absorption in noncubic europium compounds (EuS${\mathrm{O}}_4$, Eu${\mathrm{C}}_2$ ${\mathrm{O}}_4$, Eu${\mathrm{Cl}}_2$, Eu${\mathrm{CO}}_3$) shows a combined magnetic and quadrupole interaction at very low temperatures. The nuclear quadrupole moment ratio for ${\mathrm{Eu}}^{151}$, $\frac{Q\left(21.6\mathrm{} \mathrm{keV}\right)}{Q\left(\mathrm{ground}\right)}=1.30\mathrm{}\pm 0.05$, was obtained from measurements at 0.054°K. With $Q\left(\mathrm{ground}\right)=1.16\mathrm{}$ b, we find $Q\left(21.6\mathrm{} \mathrm{keV}\right)=1.51\mathrm{}$ b. Earlier measurements are discussed in view of the present results.