0+ levels of even nuclei in the rare-earth region

Abstract

The quadrupole vibrations of beta type of deformed nuclei have been found in only a few cases in the heavy element region. We started a search in order to find such levels also in the rare-earth region. A 0+ level of beta vibrational type at 685.0 keV was found in the deformed nucleus Sm152 by measuring conversion coefficients. Its corresponding 0+ level of two-phonon type was observed in Gd152 at 615.3 keV. The strongly deformed nucleus Er166 has a 0+ level at 1460.4 keV now confirmed by angular correlation measurements. The 1087 keV level in Os188 and the 1267 keV level in the spherical nucleus Pt194 were also measured by angular correlation to have zero spins, indicating the same trend of the 0+ levels as theoretically expected. (A second excited 0+ level was found in Os188 at 1766 keV and in Pt194 at 1480 keV.) When the beta and gamma vibrational bands are known, the theoretical and experimental rotational-vibrational coefficients can be compared: Btheory = kBexp. A k-value of 2–4 is found, indicating a weaker coupling than that theoretically expected. The experimental trend of levels in even nuclei with A = 50–250 is discussed, and some new spin assignments are proposed.