Ground-state configuration of neutron-rich ³⁵Al via Coulomb breakup

Abstract

The ground-state configuration of ³⁵Al has been studied via Coulomb dissociation (CD) using the LAND-FRS setup (GSI, Darmstadt) at a relativistic energy of ~ 403 MeV/nucleon. The measured inclusive differential CD cross section for ³⁵Al, integrated up to 5.0 MeV relative energy between the ³³Al core and the neutron using a Pb target, is 78(13) mb. The exclusive measured CD cross section that populates various excited states of ³³Al is 29(7) mb. The differential CD cross section of ³⁵Al -> ³⁴Al + n has been interpreted in the light of a direct breakup model, and it suggests that the possible ground-state spin and parity of ³⁵Al could be, tentatively, 1/2⁺ or 3/2⁺ or 5/2⁺. The valence neutrons, in the ground state of ³⁵Al, may occupy a combination of either l = 3,0 or l = 1,2 orbitals coupled with the ³⁴Al core in the ground and isomeric state(s), respectively. This hints of a particle-hole configuration of the neutron across the magic shell gaps at N = 20,28 which suggests narrowing the magic shell gap. If the 5/2⁺ is the ground-state spin-parity of ³⁵Al as suggested in the literature, then the major ground-state configuration of ³⁵Al is a combination of ³⁴Al (g. s.; 4⁻) circle times ν_(p_(3/2)) and ³⁴Al (isomer; 1⁺) circle times ν _(d_(3/2)) states. The result from this experiment has been compared with that from a previous knockout measurement and a calculation using the SDPF-M interaction.