Measurement of the Ground State Spin and Parity of Al22 Disfavors Halo Formation
Journal article, 2026
We report the decisive resolution of the ground state spin and parity of the proton–drip line nucleus Al22, a prime candidate for a proton halo. The resolution stems from the first β-delayed charged particle emission experiment in the gas stopping area at the Facility for Rare Isotope Beams (FRIB), leveraging high-intensity, low-energy beams extracted from the Advanced Cryogenic Gas Stopper (ACGS). The pristine beam quality from FRIB and the ACGS enabled a sensitive particle identification technique using thin silicon detectors, allowing for the suppression of the dominant proton background and the first observation of the weak β-delayed α transition from the isobaric analog state in Mg22 to the Ne18 ground state. This observation uniquely fixes the Al22 ground state as 4+. The valence proton is confined by a dominant d-wave centrifugal barrier which, combined with the Coulomb repulsion, hinders the tunneling required for halo formation despite the exceptionally low proton separation energy of Al22
Author
Erik Asbjörn Mikkelsen Jensen
Aarhus University
Chalmers, Physics, Subatomic, High Energy and Plasma Physics
J. S. Nielsen
Aarhus University
B. S.O. Johansson
Aarhus University
A. Adams
Michigan State University
J. Dopfer
Michigan State University
C. S. Sumithrarachchi
Michigan State University
L. J. Sun
Michigan State University
L. E. Weghorn
Michigan State University
Tyler Wheeler
Michigan State University
C. Wrede
Michigan State University
M. Borge
Spanish National Research Council (CSIC)
O. Tengblad
Spanish National Research Council (CSIC)
M. Madurga
University of Tennessee
Björn Jonson
Chalmers, Physics, Subatomic, High Energy and Plasma Physics
K. Riisager
Aarhus University
H. O. U. Fynbo
Aarhus University
Physical Review Letters
0031-9007 (ISSN) 1079-7114 (eISSN)
Vol. 136 20 202503Atomic nuclei that merely exist
Swedish Research Council (VR) (2022-04248), 2023-01-01 -- 2026-12-31.
Subject Categories (SSIF 2025)
Subatomic Physics
DOI
10.1103/3lpm-sy41