The (p, t) reactions on nuclei in the rare earth region

Abstract

The (p, t) reactions on isotopic targets of 178, 180Hf and all the stable isotopes of Yb and on natural targets of Gd, Dy, Er, Hf, Ta, W, Os and Au were studied at a beam energy of 19 MeV with an average resolution of 12 keV. A split-pole magnetic spectrometer was used to measure (p, t) Q-values and absolute differential cross sections. On the basis of angular distribution shapes definite 0 + and tentative 2 + assignments were made. Rotational bands were identified assuming an I( I+1) spacing. The (p, t) reaction populates excited 0 + states strongly in 174Yb, 176Hf, 166Yb and several Gd, Dy and Er isotopes. The 174Yb and 176Hf 0 + states are discussed in terms of the pairing phase transition and in terms of Nilsson orbitals with unequal (p, t) reaction amplitudes. Members of gamma and octupole vibrational bands were observed in the even- N nuclei. The lowest L = 0 transfers to states in 169, 171Yb were found to have less than 55% of the strength to ground states in adjacent even- N nuclei. A strong L = 0 transfer to a state at 1513 keV in 171Yb indicates the presence of a possible K = 0 core vibration coupled to the unpaired 5 2 [512] neutron. The natural targets have furnished information on trends in cross sections for members of ground bands, gamma bandheads, 3 − octupole states, and strongly excited 0 + states.