Octupole excitations in 141,144Cs and the pronounced decrease of dipole moments with neutron number in odd-Z neutron-rich 141,143,144Cs

The level scheme of odd-Z neutron-rich 141Cs (image, image) was extended and expanded and that of 144Cs (image) was identified for the first time by means of image coincidence measurements of prompt γ rays in the spontaneous fission of 252Cf with Gammasphere. Spin/parity was assigned to the levels based on angular correlations and level systematics in 141,143Cs. Parity doublets characteristic of both simplex quantum number image and image were proposed in 141Cs. The tests by using rotational frequency ratio image imply octupole vibrations in 141Cs and 143Cs. image values and electric dipole moments image were calculated for 141Cs, and re-determined for 143Cs. It was found that image values of 141Cs are simplex-dependent and the average value is one order of magnitude larger than that of 143Cs, and the deduced dipole moment image of 141Cs is considerably larger than that of 143Cs, and comparable to the image isotone 142Ba. For 144Cs the yrast sequence looks like a well-deformed rotational band, but no octupole band structure was identified in this nucleus. The overall variations of image in 141,143,144Cs exhibit a pronounced drop of dipole moment with increasing neutron number in this odd-Z isotopic chain, which may be analogous in nature to the quenching of image observed in even–even 146Ba (image, image) and 224Ra (image, image), and to the drop of image in the odd-Z neutron-rich 147La (image, image) reported by our collaboration.