Structural connections between 148Sm and 149Sm nuclei

The ^{146, 148}Nd(α, χn) and ^{148, 150}Nd(³He, χn) reactions at E_α = 20–43 MeV and E_3He = 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 I^π = 10⁺ is predominantly populated. A negative-parity odd-spin band extending from I^π = 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 $\text{25}\text{2}$ and negative-parity levels with spins up to $\text{21}\text{2}$ are observed. The predominant γ-decay proceeds via transitions associated with $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$, $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$, $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ 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 $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ state in ¹⁴⁹Sm is found. Experimental evidence is presented to interprete the $\text{1}\text{2}{}^{\mathrm{+}}$, $\text{15}\text{2}{}^{\mathrm{+}}$, … and $\text{9}\text{2}{}^{\mathrm{?}}$, $\text{13}\text{2}{}^{\mathrm{?}}$, …, ΔI = 2, sequences in ¹⁴⁹Sm as arising from the coupling of an $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ neutron to the octupole and quadrupole modes of the ¹⁴⁸Sm core nucleus. The absolute reaction cross sections for the ^{146, 148, 150}Nd(³He, χn) reactions have been determined for different bombarding energies. The mixing of the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ shells is discussed in the framework of an axial-particle-rotor model calculation.