nucl-ex digest · Jul 20, 2026

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

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

^{40}

Si and the first simultaneous lifetime and heavy-ion inelastic-scattering measurements in

^{41}

Si. In

^{40}

Si, the extracted lifetimes for the

2_{1}^{+}

and

(2_{2}^{+})

states indicate moderate quadrupole collectivity at

N = 26

, together with signatures of triaxiality. In

^{41}

Si, two near-degenerate states at 570 and 658~keV exhibit comparable

B (E 2)

strengths as extracted from inelastic scattering, while the measured lifetimes indicate dominant

M 1

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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Universal Properties of Near-Threshold Single-Neutron Resonances

Myungkuk Kim · Young-Ho Song · Hans-Werner Hammer🇩🇪 · Youngman Kim🇰🇷 · Dean Lee🇺🇸 · Yuan-Zhuo Ma🇺🇸

We establish universal width predictions for near-threshold single-neutron resonances in $L > 0$ partial waves. Our results go beyond Wigner's well-known scaling behavior of cross sections near threshold. We show that the finite square-well potential exhibits discrete scale invariance at zero energy. From this fact, we derive an analytic baseline for the resonance width that depends only on geometry, angular momentum, and resonance energy, and not on internal short-distance nuclear details or radial excitation. This is a nontrivial property that is unique to the finite square-well potential and does not occur for other potentials. Application to observed p-wave and d-wave resonances demonstrates that the square-well result provides a robust baseline. We show that discrete scale invariance erases radial-node information in the sharp-boundary limit, but realistic Woods-Saxon diffuseness breaks this invariance, suppressing the reduced width by a factor sensitive to the internal radial excitation. These results provide a simple geometric benchmark for identifying when observed neutron resonances are controlled by universal threshold physics and when they exhibit systematic deviations driven by structure-dependent effects.

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