Erhan Gülmez

Recently a new region of deformation has been predicted for Z $\leq$ 64, N $\leq$ 82 nuclei. To further establish the high angular momentum structure in this region and to probe the onset of this deformation we have studied the gamma-ray deexcitation of states in $\sp{140}$Nd and $\sp{141}$Pm.

The states in $\sp{140}$Nd were populated via the $\sp{126,128}$Te($\sp{18,16}{\rm O{,}4n})$ reactions. Excitation functions for both reactions were measured over a beam energy range of 64-76 MeV and 72-76 MeV, respectively, with 2 MeV increments. Gamma-ray angular distribution and gamma-gamma coincidence data were taken with a 76 MeV $\sp$O beam and a 72 MeV $\sp$O beam, respectively. From these data a level spectrum up to E$\sb{\rm x}$ $\sim$ 6.4 MeV and I = 17 has been obtained. Above the 7$\sp-$ and 10$\sp+$ isomers several new bands were found. Shell model calculations using a modified surface delta residual interaction were performed for $\sp{140}$Nd.

The gamma-ray deexcitation of states in $\sp{141}$Pm was studied via the $\sp{126}$Te($\sp$F,4n gamma) reaction. Excitation function measurements were carried out over a beam energy range of 74-84 MeV. Gamma-ray angular distribution and gamma-gamma coincidence data were taken with 80 MeV and 78 MeV $\sp$F beams, respectively. A level spectrum up to E$\sb{\rm x}\sim$ 4.8 MeV has been developed. The low-lying levels of $\sp{141}$Pm can be interpreted as a valence proton coupled to the core within a simple particle-core coupling model or the excitations of three valence particles, for example, a proton and two neutron holes.