Eur. Phys. J. A (2006) 27: 309-314
https://doi.org/10.1140/epja/i2006-08-047-0

Nuclear Physics in Astrophysics II

Study of the N = 28 shell closure in the Ar isotopic chain

A SPIRAL experiment for nuclear astrophysics

¹ IPN, IN2P3-CNRS, F-91406, Orsay Cedex, France
² GANIL, BP 55027, F-14076, Caen Cedex 5, France
³ Institute of Nuclear Research, Pf. 51, H-4001, Debrecen, Hungary
⁴ Department of Physics, Florida State University, 32306, Tallahassee, FL, USA
⁵ Institut für Kernchemie, Universität Mainz, D-55128, Mainz, Germany
⁶ FLNR/JINR, 141980, Dubna, Moscow Region, Russia
⁷ CEA-Saclay, DAPNIA-SPhN, F-91191, Gif-sur-Yvette Cedex, France
⁸ IReS, Univiversité Louis Pasteur, F-67037, Strasbourg Cedex, France
⁹ Departement für Physik und Astronomie, Universität Basel, Switzerland

^* e-mail: gaudefroy@ganil.fr

Received: 17 June 2005
Accepted: 20 December 2005
Published online: 15 March 2006

Abstract

The structure of the neutron-rich nucleus ⁴⁷Ar has been investigated through the d( ⁴⁶Ar, ⁴⁷Ar)p transfer reaction. The radioactive beam of ⁴⁶Ar at 10A·MeV was provided by the SPIRAL facility at GANIL. The protons corresponding to a neutron pick-up on bound or unbound states mechanism in ⁴⁷Ar nuclei were detected at backward angles by the position-sensitive Si array-detector MUST. The transfer-like ejectiles were detected in the SPEG spectrometer. Level scheme, spin assignments and spectroscopic factors have been deduced for ⁴⁷Ar and compared to shell model predictions. They suggest a slight erosion of the N = 28 shell gap from the weakening of the spin-orbit interaction arising from the f and p orbitals. These spectroscopic information are subsequently used to infer (n,γ) reaction rates in the Ar isotopic chain to understand the origin of the ⁴⁸Ca/ ⁴⁶Ca abnormal isotopic ratio observed in certain inclusions of meteorites.