Study of the N = 28 shell closure in the Ar isotopic chain A SPIRAL experiment for nuclear astrophysics
Résumé
The structure of the neutron-rich nucleus $^{47}$Ar has been investigated through the d( $^{46}$Ar, $^{47}$Ar)p transfer reaction. The radioactive beam of $^{46}$Ar 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 $^{47}$Ar 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 $^{47}$Ar 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,$\gamma$) reaction rates in the Ar isotopic chain to understand the origin of the $^{48}$Ca/ $^{46}$Ca abnormal isotopic ratio observed in certain inclusions of meteorites.