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Open Access Publications from the University of California

Level structure of 141Ba and 139Xe and the level systematics of N=85 even-odd isotones


New level schemes of $^{141}$Ba and $^{139}$Xe are proposed from the analyses of spontaneous-fission gamma data from our $^{252}$Cf spontaneous fission Gammasphere runs of 1995 and 2000. By analogy with the N = 85 even-odd isotones $^{149}$Gd, $^{147}$Sm, and $^{145}$Nd, spins and parities were assigned to the observed excited states in $^{141}$Ba and $^{139}$Xe. It appears that spherical shell model neutron excitations plus octupolephonons are an appropriate basis at the lower end of the bands. Going to higher spins it is clear that the soft rotor involving valence protons as well as neutrons becomes increasingly important in the configurations. Level systematics in the N = 85 even-odd isotones from Gd(Z=64) through Te(Z=52), are discussed. The excitation systematics and smooth trends of the analogous levels support the spin and parity assignment for excited levels observed in $^{141}$Ba and $^{139}$Xe. The level systematics and the comparison with neighboring even-even isotopes indicate that quadrupole and octupole collectivity play roles in $^{141}$Ba and $^{139}$Xe. From Gd(Z=64) through Te(Z=52), increasing excitation energies of the 13/2$^{+}$ states and lowering relative intensities of the positive parity bands in the N = 85 even-odd isotones may indicate that the octupole strength is becoming weaker for the isotones when approaching the Z = 50 closed shell.

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