Rapid structural evolution of neutron-rich silicon isotopes toward N = 28

2026/07/17 by G. L. Zimba, H. Iwasaki, B. A. Brown +27
#nucl-ex #nucl-th

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Abstract

Neutron-rich Si isotopes represent a unique case of shell evolution, exhibiting a robust shell closure at N=20 and pronounced quadrupole collectivity at N = 28. We report lifetime measurements of excited states in ⁴⁰Si and the first simultaneous lifetime and heavy-ion inelastic-scattering measurements in ⁴¹Si. In ⁴⁰Si, the extracted lifetimes for the 2₁⁺ and (2₂⁺) states indicate moderate quadrupole collectivity at N=26, together with signatures of triaxiality. In ⁴¹Si, two near-degenerate states at 570 and 658~keV exhibit comparable B(E2) strengths as extracted from inelastic scattering, while the measured lifetimes indicate dominant M1 decays. The combined lifetime and inelastic-scattering results suggest an evolution toward oblate shape, consistent with large-scale shell-model predictions.

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