Mixed symmetry in the vibrational nucleusCe142

Low-lying levels of the nucleus ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ce}$ have been studied by Coulomb excitation with ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ projectiles to determine various $B\left(E\lambda \right)$ values and the static quadrupole moment $Q\left(2_1^{+}\right)$. Excellent agreement is found between the observed properties and predictions made using the U(5) limit of the proton-neutron interacting boson model. The results strongly support the contention that the $2_3^{+}$, 2.004-MeV level has mixed proton-neutron symmetry. Combining the present measurement for $B(E2;0_1^{+}\to 2_3^{+})$ of $0.070\pm 0.011 e^2{b}^2$ with known branching and mixing ratios gives a substantial $M1\mathrm{}$ strength of $(0.26\mathrm{}\pm 0.05){\mu }_N^2$ for the $2_3^{+}$ → $2_1^{+}$ transition.