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Direct experimental evidence for a multiparticle-hole ground state configuration of deformedMg33

Physical review. C2016Vol. 94(3)

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Abstract

The first direct experimental evidence of a multiparticle-hole ground state configuration of the neutron-rich $^{33}\mathrm{Mg}$ isotope has been obtained via intermediate energy (400 A MeV) Coulomb dissociation measurement. The major part $\ensuremath{\sim}(70\ifmmode\pm\else\textpm\fi{}13)%$ of the cross section is observed to populate the excited states of $^{32}\mathrm{Mg}$ after the Coulomb breakup of $^{33}\mathrm{Mg}$. The shapes of the differential Coulomb dissociation cross sections in coincidence with different core excited states favor that the valence neutron occupies both the ${s}_{1/2}$ and ${p}_{3/2}$ orbitals. These experimental findings suggest a significant reduction and merging of $sd\ensuremath{-}pf$ shell gaps at $N\phantom{\rule{4.pt}{0ex}}\ensuremath{\sim}20$ and 28. The ground state configuration of $^{33}\mathrm{Mg}$ is predominantly a combination of $^{32}\mathrm{Mg}(3.0,3.5\phantom{\rule{0.16em}{0ex}}\mathrm{MeV};{2}^{\ensuremath{-}},{1}^{\ensuremath{-}})⨂{\ensuremath{\nu}}_{{s}_{1/2}}$, $^{32}\mathrm{Mg}(2.5\phantom{\rule{0.16em}{0ex}}\mathrm{MeV};{2}^{+})⨂{\ensuremath{\nu}}_{{p}_{3/2}}$, and $^{32}\mathrm{Mg}(0;{0}^{+})⨂{\ensuremath{\nu}}_{{p}_{3/2}}$. The experimentally obtained quantitative spectroscopic information for the valence neutron occupation of the $s$ and $p$ orbitals, coupled with different core states, is in agreement with Monte Carlo shell model (MCSM) calculation using 3 MeV as the shell gap at $N=20$.

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Abstract

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