Configuration mixing in even-even ${}^{148-154}\mathrm{Sm}$ within the interacting boson model

The interacting boson model with configuration mixing due to two-particle–two-hole excitations is applied to describe even-even ${}^{148-154}\mathrm{Sm}$ to investigate the cross-shell excitation effects in these nuclei. It is shown from the fitting results to the experimentally known positive-parity level energies, $B\left(E2\right)$ values, and electric quadrupole moments that the IBM configuration mixing (CM) describes these nuclei better than the IBM consistent-$Q$ formalism without the configuration mixing. Especially, the IBM-CM fitting results to the known $B\left(E2\right)$ values are significantly improved. Furthermore, it is shown from the IBM-CM fitting results that the intruder configuration turns to be always dominant in the $0_2^{+}, 2_2^{+}$, and $4_2^{+}$ states of well-deformed ${}^{150,152,154}\mathrm{Sm}$. Most notably, there is a clear normal-intruder configuration crossover along the yrast line of these nuclei described by the IBM-CM.

Figure 1

Level energies (in MeV) of the experimentally identified positive-parity bands of ${}^{148}\mathrm{Sm}$ and ${}^{150}\mathrm{Sm}$, where the left (black) levels are those obtained from the experiments, the middle (red) levels are those obtained from the IBM-CM, and the right (blue) levels are those obtained from the original $\mathrm{C}Q$ formalism.

Figure 2

The same as Fig. 1, but for ${}^{152}\mathrm{Sm}$ and ${}^{154}\mathrm{Sm}$.

Figure 3

Four typical $B\left(E2\right)$ values and the ratio $R=B(E2;2_3^{+}\to 0_2^{+})/B(E2;2_3^{+}\to 0_1^{+})$ of ${}^{148,150,152,154}\mathrm{Sm}$.

Figure 4

The same as Fig. 1, but for ${}^{152}\mathrm{Sm}$ and ${}^{154}\mathrm{Sm}$.

Figure 5

$B(E2;L\to L-2)$ along the yrast line as a function of $L$ of ${}^{152,154}\mathrm{Sm}$ in the IBM-CM with comparison to the experimental data and the $\mathrm{C}Q$ formalism data.