Orateur
Description
The evolution of nuclear shell structure in exotic nuclei provides key insights into the
fundamental nature of nuclear forces. In nuclei far from stability, conventional magic
numbers can disappear, while new ones may emerge, a phenomenon known as shell evolution [1].
A well-known example is the evolution of the N=28 shell gap from $^{40}$Ca to $^{48}$Ca,
which has been successfully explained by three-nucleon (3N) forces [2]. Similarly, the
N=14 shell gap in oxygen isotopes shows a comparable trend [3]. These studies highlight
the crucial role of many-body interactions in shaping shell structure.
To extend our
understanding to heavier nuclei, we investigate the evolution of the N=50 shell gap
for which the isotopic chain of Ni would be the perfect candidate.
An experiment was
carried out at GANIL to study $^{68}$Ni via (p,d) and (d,p) reactions, as this nucleus
is the anchor point to determine the amplitude of the N=50 shell gap in $^{78}$Ni, from
relatively well known neutron-neutron effective interaction from experimental data. By
performing neutron-adding and neutron-removing reactions on $^{68}$Ni, we also get a
unique access to the spectroscopic strengths and thus, the occupancy of the orbitals
below and above N=40. This allows to characterize the magicity at N=40. Indeed, depending
on whether a sharp occupancy drop is observed or not, the nucleus can be concluded to
have either a magic or a superfluid nature [4]. Moreover, it is also planned to
deduce the information on the 2p$_{1/2}$ - 2p$_{3/2}$, 1g$_{7/2}$ - 1g$_{9/2}$ and
1f$_{5/2}$ - 1f$_{7/2}$ spin-orbit splittings.
In this contribution, I will present the status of the ongoing analysis
and the results obtained so far, with particular emphasis on
the (d,p) channel. Some preliminary results on the (p,d) channel will also be presented.
References
[1] O. Sorlin and M.G. Porquet, Prog. Part. Nucl. Phys. 98, 602-673 (2008).
[2] J. D. Holt et al., J. Phys. G: Nucl. Part. Phys. 39, 085111 (2012).
[3] T. Otsuka et al., Phys. Rev. Lett. 105, 032501 (2010).
[4] O.Sorlin, S.Leenhardt, C.Donzaud, J.Duprat, F. Azaiez, et al., Phys. Rev. Lett. 88, 092501 (2002).