Spin and Magnetic Moment ofMg33: Evidence for a Negative-Parity Intruder Ground State

Abstract

We report on the first determination of the nuclear ground-state spin of 33Mg, I=3/2, and its magnetic moment, mu= -0.7456(5) mu(N), by combining laser spectroscopy with nuclear magnetic resonance techniques. These values are inconsistent with an earlier suggested 1 particle-1 hole configuration and provide evidence for a 2 particle-2 hole intruder ground state with negative parity. The results are in agreement with an odd-neutron occupation of the 3/2 [321] Nilsson orbital at a large prolate deformation. The discussion emphasizes the need of further theoretical and experimental investigation of the island of inversion, a region previously thought to be well understood.

In-beamγ-ray spectroscopy ofMg35and

“…These collective properties of even-even nuclei are rather well described by state-of-the-art Monte Carlo Shell-Model (MCSM) calculations (SDPF-M effective interaction) that allow for unrestricted mixing of neutron particle-hole configurations across the N = 20 shell gap. However, experimental information on their odd-N neighbors, 31,33 Mg [15][16][17][18][19][20][21][22] and 30 Na [23], for example, has posed significant challenges for these calculations and led to controversial interpretations, indicating that odd-A and odd-odd nuclei pose very stringent benchmarks for a shell model description of this region.…”

Isobaric analog resonances of theN=21nucleus35Si

“…In the common picture explaining the shell breaking, there remain problems in the shell structure in this region. The experimental results for the spin-parity J π of the ground state in 33 Mg obtained in various studies are inconsistent with each other [8][9][10][11].…”

“…Around 5 MeV, we observed two peaks. [32]) and 33 Mg (Yordanov [9], Tripathi [10]) are shown for comparison in (d) and (e), respectively.…”

Intermediate energy proton knockout to the “island of inversion” isotopeMg31

“…The cocktail beam was 71% pure 32 Al with the remainder being 33 Si. The fully-stripped secondary beam emerged from the magnetic separator with an energy of 91 MeV/nucleon and then underwent reactions on a 1 mm (185 mg/cm 2 ) 9 Be target. The thickness of the target and momentum acceptance were chosen such that their contribution to the total momentum distribution was small compared to the contribution from the reaction.…”

“…Recent measurements of the groundstate spins and parities of magnesium isotopes [8][9][10] have provided important information about the energetically favored configurations in this region. Neutron-knockout experiments performed in the region [11] are also a powerful tool to deduce the single-particle occupancies in the ground state of these nuclei, showing the dominance of the 0hω configurations in 30 Mg.…”