Nuclei in the N=20 island of inversion, located around the neutron-rich 32Mg isotope, have ground-states dominated by deformed and collective configurations arising from neutron-pair excitations across the shell gap (See Ref.  for a recent review). Particle-hole sd-pf cross-shell intruder configurations have also been observed in the low-lying level scheme of heavier N = 20 even-even nuclei. However, the expected 1/2_2 intruder bandhead has not yet been identified in the odd-even nucleus 35P. Previous attempts to identify this state suffered from a large background in the region of interest arising from contaminants in the target .
We will report on a recent measurement using the 36S(d, 3He)35P reaction in inverse kinematics with the Helical Orbit Spectrometer (HELIOS) at ATLAS/ANL . Thanks to the unique capabilities of HELIOS, enhanced with a recoil detector setup, it is possible to perform the reaction in nearly background free conditions.
An analysis of the reconstructed 3He spectrum in HELIOS did not show a peak that could be associated with the 1/2_2 intruder state. We have not observed any candidate state in the region of interest with an intensity greater than 5% of the ground-state. This in turn can be used to set a limit to the amount of 2p2h excitations in the 36S ground state wavefunction. These results provide an additional constraint to state-of-the-art theoretical descriptions to further understand the evolution of shell structure in the region.
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