Binary-reaction spectroscopy ofMo99,100: Intruder alignment systematics inN=57andN=58isotones

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Abstract

The near-yrast states of $^{99,100}\mathrm{Mo}$ have been studied following their population via a binary reaction between a $^{136}\mathrm{Xe}$ beam and a thin, self-supporting $^{100}\mathrm{Mo}$ target. The yrast sequence in $^{100}\mathrm{Mo}$ has been extended to a tentative spin∕parity $({20}^{+})$, while the decoupled band built on the ${I}^{\ensuremath{\pi}}={\frac{11}{2}}^{\ensuremath{-}}$ isomeric state in $^{99}\mathrm{Mo}$ has been extended through the first alignment up to a tentative spin∕parity of $({\frac{43}{2}}^{\ensuremath{-}})$. The results are compared with self-consistent, cranked-mean-field calculations using a Woods-Saxon potential. The alignment systematics of the intruder ${h}_{11∕2}$ bands in the $N=57$ isotones from Mo $(Z=42)$ to Cd $(Z=48)$ and the yrast sequences in their $N=58$ even-even neighbors are discussed. An overall picture emerges, where the alignment properties evolve from being due to positive-parity neutrons in the $_{48}^{105}\mathrm{Cd}$ to predominantly ${({g}_{9∕2})}^{2}$ proton crossings closer to the $Z=40$ subshell. Qualitatively, this can be explained by an increase in the quadrupole deformation and a simultaneous lowering of the proton Fermi surface in the ${g}_{9∕2}$ shell with decreasing proton number. These data provide excellent examples of rotational-alignment phenomena in weakly deformed nuclei.

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