Structure of ^{36}Ca under the Coulomb Magnifying Glass

Area of Science:

• Nuclear Physics
• Atomic and Molecular Physics

Background:

• Neutron-deficient nuclei provide insights into nuclear structure and stability.
• Mirror nuclei, like ^{36}Ca and ^{36}S, offer unique opportunities to study isospin symmetry and its breaking.

Purpose of the Study:

• To perform detailed spectroscopy of the ^{36}Ca nucleus.
• To investigate the energy levels and structure of ^{36}Ca, particularly focusing on potential intruder states.
• To compare the observed properties with its mirror nucleus, ^{36}S, to understand mirror energy differences (MEDs).

Main Methods:

• Utilized ^{37}Ca(p,d)^{36}Ca and ^{38}Ca(p,t)^{36}Ca transfer reactions for spectroscopy.
• Produced radioactive ^{36}Ca nuclei using the LISE spectrometer at GANIL.
• Employed the MUST2 detector array for ejectile detection and a zero-degree system for heavy residue identification.

Main Results:

• Identified an intruder 0_{2}^{+} state at 2.83(13) MeV in ^{36}Ca, located below the first 2_{1}^{+} state.
• Observed a significant mirror energy difference (MED) of -516(130) keV for the 0_{2}^{+} state, causing an inversion compared to ^{36}S.
• Tentatively identified a 0_{3}^{+} state at 4.83(17) MeV, possibly exhibiting a bubble structure with 2s_{1/2} neutron vacancies.

Conclusions:

• The observed inversion of 0^{+} and 2^{+} states in ^{36}Ca is attributed to large MEDs, particularly for the 0_{2}^{+} state.
• Shell model calculations support the intruder nature of the 0_{2}^{+} state, arising from proton excitations across the Z=20 shell closure.
• This study highlights ^{36}Ca as a system with exceptionally large MEDs, offering valuable data for nuclear structure theories.