Configuration mixing in even-even Sm148−154 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 ^148-154Sm 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, $B(E2)$ 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 $B(E2)$ 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 0₂⁺, 2₂⁺, and 4₂⁺ states of well-deformed 150,152,154Sm. Most notably, there is a clear normal-intruder configuration crossover along the yrast line of these nuclei described by the IBM-CM.