Appearance of deformation in the yttrium isotopic chain (Vol. 48, No. 3)

Evolution of deformation across Y isotopic chain.

In the isotopes of rubidium (Rb), strontium (Sr), ittrium (Y), zirconium (Zr) and niobium (Nb) (i.e., with Z=37-41), a sudden change of the nuclear structure occurs when the number of neutrons reaches N=60. While the nuclei with N<60 exhibit spherical shape in their ground states, the isotopes with N≥60 are significantly deformed. This phenomenon is considered the most dramatic shape change in the nuclear chart. A question was raised of whether the deformed structures appear just at N=60 or they reside also in the lighter isotopes. Indeed, deformed rotational bands built on the excited isomeric states are placed in 95Rb, 96Sr, 98Y, 98-99Zr, i.e., at N=58 and 59, however, nothing was known about location of such collective excitations at N<<58. In our work, it was possible to significantly develop the level scheme of 96Y57 via gamma-coincidence spectroscopy technique. During the analysis, a new 201(30)-ns isomeric state at 1655 keV excitation energy was located and the existence of a rotational band built on it was suggested. This result points to the presence of deformed structures already at N=57 which, with the increasing number of neutrons, gradually decrease in energy, to become dominant at N≥60.

L. W. Iskra and 35 co-authors, New isomer in 96Y marking the onset of deformation at N = 57, EPL 117, 12001 (2017)