We examined the ratios of neutron and proton transition matrix elements, $M_n/M_p$, for the $0_{gs}^{+}\to 2_1^{+}$ transitions in 48 even-even stable nuclei with $N>20$ for which electromagnetic matrix elements were compiled by Pritychenko et al. and for which high-quality inelastic proton-scattering data were available. Several deformed rare-earth nuclei have $(M_n/M_p)/(N/Z)$ values significantly below 1.0, which is not consistent with a simple liquid-drop picture. However, this phenomenon can be explained using a schematic picture in which $M_p$ reaches a maximum at proton midshell ($Z=66$) and $M_n$ reaches its maximum at neutron midshell ($N=104$). Several midmass vibrational nuclei have $M_n/M_p$ values significantly below $N/Z$, which is not consistent with the expectation that $M_n/M_p=N/Z$ in such nuclei. A shell-model investigation of these observations might yield insights about this behavior.

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• Collective levels
• Coulomb excitation
• Electromagnetic transitions
• Inelastic scattering reactions
• Collective models