First isomeric quadrupole moment measured in fragmentation reactions: The case ofFe61m(9/2+)

Abstract

This paper demonstrates the feasibility of quadrupole moment measurements on isomeric levels populated in projectile fragmentation reactions. The neutron-rich $^{61}\mathrm{Fe}$$(9/{2}^{+})$ [${E}^{*}=$ 861 keV, ${T}_{1/2}=$ 239(5) ns] isomer was produced and spin aligned by the intermediate energy fragmentation of a $^{64}\mathrm{Ni}$ beam and implanted in a Cd single crystal. Its spectroscopic quadrupole moment $|{Q}_{s}|=41(6)\phantom{\rule{0.3em}{0ex}}e\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{2}$ agrees with mean-field based calculations using the finite-range Gogny force, suggesting a moderately deformed shape characterized by an intrinsic charge quadrupole moment ${Q}_{0}=\ensuremath{-}85\phantom{\rule{0.3em}{0ex}}e\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{2}$ or ${Q}_{0}=+115\phantom{\rule{0.3em}{0ex}}e\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{2}$. The present measurement paves the way for future determinations of isomeric quadrupole moments in more exotic nuclei.