The nucleon-pair shell model truncated to the $S-D$ subspace is applied to nucleus ${}^{134}\mathrm{Ba}$ for examining the effects on collectivity due to long-range $n-p$ quadrupole forces. It is found that symmetric and mixed-symmetric states, consequently $M1\mathrm{}$ transitions, are primarily controlled by the $n-p$ quadrupole interaction. In comparison with surface-$\delta$ interaction, when the quadrupole $n-p$ coupling is weak, the model can produce approximately the vibrational limit, and when the quadrupole $n-p$ coupling is strong, the O(6) limit can be realized.

• Received 2 January 2001

DOI:https://doi.org/10.1103/PhysRevC.64.037303