Restrictions on shape-coexistence descriptions of A ~ 150 nuclei from the 156Dy(p, t) 154Dy reaction

The 156 Dy(p, t), 154 Dy reaction was studied, using 20 MeV protons and a magnetic spectrograph to analyze the reaction products. This reaction on the "deformed" target 156 Dy has three strong L = 0 transitions populating levels in the "spherical" nucleus 154 Dy at 0, 661, and 1058 keV with relative strengths of 100:74:16, respectively. This population pattern is similar to those observed in the isotones 152 Gd and, 150 Sm, in which the third 0 + bands have been interpreted as deformed bands coexisting in spherical nuclei. However, the third 0 + band in 154 Dy has a rotational energy spacing as large as that for the ground-state band, which suggests that it does not have a large deformation, and its (p, t) strength is significantly less than those for the corresponding states in the samarium and gadolinium isotones. This restricts the shape-coexistence interpretation of excited 0 + states in 154 Dy. The systematics suggest that, 152 Gd is probably also not as good an example of shape coexistence as 150 Sm.