# Structure of 9C through proton resonance scattering with Texas Active Target detector

## TL;DR

This study investigates the level structure of the exotic nucleus 9C using proton resonance scattering with an active target, identifying a new positive parity state and clarifying the sd-shell location in this neutron-deficient isotope.

## Contribution

The paper reports the first identification of a 5/2+ resonance at 4.3 MeV in 9C, providing new insights into its shell structure and spin-parity assignments.

## Key findings

- First positive parity state identified in 9C at 4.3 MeV
- Determined the energy of the 2s shell in 9C
- Confirmed the 5/2+ resonance as a broad L=0 state

## Abstract

Background: Level structure of the most neutron deficient nucleon-bound carbon isotope, 9C, is not well known. Definitive spin-parity assignments are only available for two excited states. No positive parity states have been conclusively identified so far and the location of the sd-shell in A=9 T=3/2 isospin quadruplet is not known. Purpose: We have studied the level structure of exotic nucleus 9C at excitation energies below 6.4 MeV. Methods: Excited states in 9C were populated in 8B+p resonance elastic scattering and excitation functions were measured using active target approach. Results: Two excited states in 9C were conclusively observed, and R-matrix analysis of the excitation functions was performed to make the spin-parity assignments. The first positive parity state in A=9 T=3/2 nuclear system, the 5/2+ resonance at 4.3 MeV, has been identified. Conclusions: The new 5/2+ state at 4.3 MeV in 9C is a single-particle L=0 broad resonance and it determines the energy of the 2s shell. The 2s shell in this exotic nucleus appears well within the region dominated by the p-shell states.