Structure of 10He low-lying states uncovered by correlations

Area of Science:

• Nuclear Physics
• Exotic Nuclei Research
• Nuclear Structure

Background:

• Understanding the structure of exotic nuclei like Helium-10 (10He) is crucial for testing nuclear models.
• The N=8 shell closure is a key feature in nuclear physics, observed in stable and some unstable nuclei.
• Previous studies on Beryllium-12 (12Be) indicated a breakdown of the N=8 shell.

Purpose of the Study:

• To investigate the ground state properties and low-lying excited states of the exotic 10He nucleus.
• To determine the level ordering and structural characteristics of 10He.
• To explore the extent of the N=8 shell breakdown phenomenon in light, neutron-rich nuclei.

Main Methods:

• Production of the 10He nucleus via the 3H(8He,p)10He reaction.
• Analysis of angular correlations of 10He decay products.
• Interpretation of interference patterns to deduce nuclear structure.

Main Results:

• The 0+ ground state of 10He was identified at approximately 2.1±0.2 MeV above the breakup threshold.
• Observed angular correlations indicate a coherent superposition of excited states, including a 1- state (4-6 MeV) and a 2+ state (>6 MeV).
• An anomalous level ordering was found, with excited states appearing at lower energies than expected based on shell closure.

Conclusions:

• The experimental findings for 10He reveal an anomalous level ordering, challenging traditional nuclear shell models.
• The results suggest that the breakdown of the N=8 shell, previously observed in 12Be, extends to the 10He system.
• This study provides critical data for understanding the evolution of nuclear shell structure in exotic, neutron-rich nuclei.