g-factor and quadrupole moment of the 212− isomeric state in 131La: Signature for a weakly-deformed magnetic rotational band head

The g-factor and the static quadrupole moment of a magnetic rotational band head 212− at 2121 keV in 131La have been determined by means of the time-differential perturbed angular distribution technique. The measured value of the g-factor, +1.060(4), is in agreement with the theoretical value for a three quasi-proton, π3{112−[505]⊗52+[422]⊗52+[413]} Nilsson configuration assignment. The observed spectroscopic quadrupole moment ratio, Qs(212−,131La)Qs(192−,137La)=0.457(4), supports the collective oblate shape (γ∼−60°) with quadrupole deformation β2<0.07. The half-life of the 212− state, 37.2(1) ns, is re-measured with better accuracy.