Coulomb Excitation of Second2+States in Even-Even Medium Weight Nuclei

The location of a second $2^{+}$ state has been found for thirteen even-even medium-weight nuclei by means of Coulomb excitation produced by 8-, 9-, and 10-Mev $\alpha$ particles. The relatively weak excitation of these states is detected by a coincident measurement of the cascade gamma rays. From the observed gamma-ray yields, information is obtained on the $B\left(E2\mathrm{}\right)\text{'}\mathrm{s}$ for the crossover transitions. The cross over $B\left(E2\mathrm{}\right)\text{'}\mathrm{s}$ exhibit some uniformity and are all rather weak, being about single-particle value or a little less. For some nuclei the cascades/crossovers ratio for the second $2^{+}$ state is known from other work, and it is then possible to extract the $B\left(E2\mathrm{}\right)\mathrm{}$ for the upper cascade transition. These upper cascade $B\left(E2\mathrm{}\right)\text{'}\mathrm{s}$ exhibit enhancements comparable to those for the lower cascade transitions. Evidence is obtained for the "double $E2\mathrm{}$" Coulomb excitation of the $4^{+}$ state in ${\mathrm{Cd}}^{114}$ and this requires an enhanced $4\to 2B\left(E2\mathrm{}\right)\mathrm{}$. In general, the measurements reported support a collective model interpretation, but it is as yet difficult to draw conclusions concerning the shape of the collective potential energy surface governing this motion.