Extremely asymmetric shears band in $^{143}$Sm
Résumé
A dipole sequence has been observed and investigated in the Sm143 nucleus populated through the heavy-ion-induced fusion-evaporation reaction and studied using the Indian National Gamma Array as the detection system. The sequence has been established as a magnetic rotation (MR) band primarily from lifetime measurements of the band members using the Doppler shift attenuation method. A configuration based on nine quasiparticles with highly asymmetric angular momentum blades has been assigned to the shears band in light of the theoretical calculations within the framework of the shears mechanism with the principal axis cranking (SPAC) model. This is hitherto the maximum number of quasiparticles along with the highest asymmetricity associated with a MR band. Furthermore, as it has followed from the SPAC calculations, the contribution of the core rotation to the angular momentum of this shears band is substantial and greater than in any other similar sequence, at least, in the neighboring nuclei. This band can thus be perceived as a unique phenomenon of shears mechanism in operation at the limits of quasiparticle excitations as manifested in MR bandlike phenomena, evolving into collectivity.