Collective structure of tungsten nuclei

The neutron pairing character of states in 178180181W and 182184W was investigated by use of the (p,t) reaction at an incident proton energy of 21 MeV. Excitation energies and angular distributions were obtained for all states populated up to approximately 2.5 MeV of excitation. Excited J(π) = 0(+) states, many previously unreported, were populated in 178W at 997 keV (9%), 1356 keV (3%), and 1643 keV (1%); in 180W at 1516 keV (7%), 1095 keV(2%), and 2356 keV (4%); in 182W at 1135 keV (14%), 2520 keV (2%), 2552 keV (1%), and 2725 kev (3%); and in 184W at 995 keV (8%), where the numbers in parenthesis are the yields given as a percentage of the ground-state yields. Strong L = 0 transitions were also seen in the 183W(p,t)181W reaction to states at 454 keV and 1864 keV excitation. The first excited 0+ states in these isotopes can be divided into two groups, one well described in tes of a pairing-vibration scheme arising from an energy gap in the neutron single-particle level scheme occurring at N = 108, and the other interpreted as the ground state of the target nucleus coupled to two holes in a group of single-particle levels somewhat below, and decoupled from, the Fermi surface. A specific prediction of this structure model, that the L = 0 transition to the 1864 keV state in 181W should not be blocked by the unpaired neutron, is found to be fulfilled. The systematics of transitions to the J(π) = 2(+) member of the K = 2 gamma vibrational bands in these nuclei is discussed with particular attention to the determination of the main two-neutron configurations involved in the population of these states