STRUCTURAL CONNECTIONS BETWEEN SM-148 AND SM-149 NUCLEI

The 146, 148Nd(α, χn) and 148, 150Nd(3He, χn) reactions at Eα = 20-43 MeV and E3He = 19-27 MeV, are used to study excited states in the 149Sm86 and 149Sm87 nucleides and consequently the low-spin odd-parity excitation. The mixing ratios and multipolarities of the most prominent transitions are deduced from the combined evidence of angular distribution and electron conversion data. The spin-parity assignments for most of the levels observed are established. In 148Sm the ground state band extending to Iπ = 10+ is predominantly populated. A negative-parity odd-spin band extending from Iπ = 3-through 11- is also observed. The bands in 148Sm are interpreted within the framework of the interacting boson approximation model. In 149Sm positive-parity levels with spin up to 25 2 and negative-parity levels with spins up to 21 2 are observed. The predominant γ-decay proceeds via transitions associated with i 13 2, h 9 2, f 7 2 and h 11 2 intrinsic configurations. The branching ratios B(E1)/B(E2) are calculated and compared in both 148Sm and 149Sm nucleides. The B(E1)/B(E2) dependence on the value of Z for some N = 86 (as well as 88 and 84) isotones showing a minimum of Z = 64 was noted. A 4 ns high-spin isomer mainly decaying into the positive-parity band based on the i 13 2 state in 149Sm is found. Experimental evidence is presented to interprete the 1 2+, 15 2+, ... and 9 2-, 13 2-, ..., ΔI = 2, sequences in 149Sm as arising from the coupling of an h 9 2 neutron to the octupole and quadrupole modes of the 148Sm core nucleus. The absolute reaction cross sections for the 146, 148, 150Nd(3He, χn) reactions have been determined for different bombarding energies. The mixing of the f 7 2 and h 9 2 shells is discussed in the framework of an axial-particle-rotor model calculation. © 1979.