Deformation in odd-mass nuclei near A ∼ 100: one- and three-quasiparticle nilsson states in 9939Y60

Study of Intermediate-spin States of $^{98}$Y

“…The neutron-rich odd-odd 98 Y (N = 39, Z = 59) nucleus is of particular interest owing to its position on the border of a ground-state shape change. The spherical N = 56 subshell closure is still effective in 97 Y (N = 58) [11] while, with only two more neutrons, 99 Y (N = 60) has a strongly deformed ground state [12][13][14]. Shape coexistence in 98 Y has been reported.…”

On the correspondence between rotational bands in the mass regionsA ? 100 andA ? 150

“…One may now speculate that the observed slight increase in the energies of the first excited states in lOl, lO2Sr _ as mentioned above, indicating a reduction of the moments of inertia -may be correlated to a stabilizing effect of the predicted [9,10] N = 64 sub-shell gap at somewhat lower deformation than the ~z ~_0.33 found for the neighbouring isotopes 99, lOOSr" In the spherical case, the high 2~-energy of 1751 keV observed in 96 4oZr56 has been interpreted as a consequence of a strong mutual reinforcement of semi-magicity for neutron and proton sub-shells, which appears to be washed out rapidly when going away from Z = 40. In terms of shell structure, it would therefore be interesting to see if a similar mechanism may also apply to the above deformed (weak) N = 64 gap in connection with the predicted [9,10] deformed (rather strong) proton sub-shell gap for Z = 38, which replaces the spherical Z = 40 shell closure. In analogy to the spherical case, one may then expect that the increase in the energies of the first excited states in appear already for the corresponding N--63 and 64 isotones with Z < 36 and Z>40, respectively.…”

Nuclear structure of97Y in the interacting boson-fermion model

“…Thus, the high-spin states in the Y isotopes in the neighbourhood of 96Zr exhibit rather pure shell-model configurations, while already 99y has the properties of a symmetric rotor [1] and 98y seems to contain shape coexistence with a spherical ground state and a rotational band based on the 495 keV level [2].…”

“…A particularly interesting feature of this nucleus is a family of levels which are probably associated [1][2][3][4] with the g9/2 proton configuration. These levels have been disclosed through the discovery of a high-spin isomer at 3523 keV in 97y which is populated in fission and which is interpreted as a three-quasiparticle configuration with a g9/2 quasiproton involved.…”