A3F-CNS Summer School 2020

Unbound states in 16,18,20C with the R3B setup: the search for the mixed-symmetry 2+ state

19 Aug 2020, 17:10

15m

Young Scientist Session 3

Speaker

Silvia Murillo Morales (University of York)

Description

The evolution of the traditional nuclear magic numbers away from the valley of stability is an active field of research. Experimental efforts focus on providing key spectroscopic information that will shed light into the structure of exotic nuclei and understanding the driving mechanism behind the shell evolution.
Recently, ${}^{\mathrm{A}}\mathrm{N}$(p,2p)${}^{\mathrm{A}-1}\mathrm{C}$ quasi-free scattering reactions were employed at the R3B/LAND setup at GSI to measure the proton component of the $2_1^{+}$ state of ${}^{16,18,20}$C in order to investigate the $\mathrm{Z}=6$ spin-orbit shell gap towards the neutron dripline. The experimental findings support the notion of a moderate reduction of the proton $1p_{1/2}-1p_{3/2}$ spin-orbit splitting towards the neutron dripline \cite{ina1,ina2}.

We work upon the model of a two-state mixing of pure proton and pure neutron excitations to describe excited 2${}^{+}$ states in neutron-rich carbon isotopes \cite{petri, aug}. The coupling of the unperturbed proton and neutron 2${}^{+}$ states should gives rise to a second 2${}^{+}$ state of mixed symmetry character expected to be strongly populated in these (p,2p) reactions. This mixed-symmetry 2${}^{+}$ state should lie at an excitation energy of about 7 MeV, above the neutron separation energy, and thus, likely decay by neutron emission. The goal of this work is to identify this mixed-symmetry 2${}^{+}$ state. Its observation will add weight to our simple picture of describing the neutron-rich C isotopic chain, giving us great insights into the shell evolution towards the neutron dripline at Z=6.

In this contribution, I will present the current status of the experimental investigation of the structure of unbound states of ${}^{16}$C, ${}^{18}$C and ${}^{20}$C induced via quasi-free scattering $(\mathrm{p},2\mathrm{p})$ reactions from ${}^{17}$N, ${}^{19}$N, and ${}^{21}$N, respectively.

\begin{thebibliography}{}
\bibitem{ina1} I. Syndikus, \textit {Proton-knockout reactions from neutron-rich N isotopes at R${}^3$B.} Technische Universität Darmstadt, PhD thesis (2018)
\bibitem{ina2} I. Syndikus et al., \textit {Probing the $\mathrm{Z}=6$ spin-orbit shell gap with (p,2p) quasi-free scattering reactions}, submitted to Physics Letters B (2020).
\bibitem{petri} M. Petri et al., Phys. Rev. C. 86, 044329 (2012).
\bibitem{aug} A. O. Macchiavelli et al. Phys. Rev. C 90 067305 (2014).