Orateur
Description
The Z=6 shell gap in neutron-rich carbon isotopes has been a subject of debate, with recent studies claiming its prevalence in this region of the nuclear chart [1], in contradiction with recent measurements [2] and shell model predictions [3].
In order to shed more light into this subject, the structure of $^{19}$N was investigated through the proton-removal d($^{20}$O, $^{3}$He) reaction using the active target ACTAR TPC [4].
In 2022, the GANIL facility provided a pure $^{20}$O beam which was selected by the LISE3 spectrometer at 35A MeV with an intensity of 2$\cdot 10^{4}$ pps. The beam was delivered to the ACTAR TPC setup, filled with a 90/10 mixture of $D_{2}$ and $C_{4}H_{10}$ at 1 bar. The energy of the particles leaving the volume was measured in the Si pad detectors while the angle was obtained from the reconstruction of the tracks in the gas. The $E_{x}$ spectrum was built with the missing mass technique. The obtained results demonstrate the potential of the ACTAR TPC setup for future transfer reaction experiments.
The low-lying structure of $^{19}$N revealed multiple $p$-hole states with l=1 determined from the differential cross section. The location of the states that carry the largest 0p$_{1/2}$ and 0p$_{3/2}$ strength allowed for the determination of the ($\pi 0 p_{1/2}$-$\pi0p_{3/2}$) spin-orbit splitting in $^{20}$O. Our results support a reduction of the Z=6 shell gap due to the tensor force in agreement with theoretical predictions from [3] using state-of-the art interactions in this region such as YSOX and SFO-tls.
References:
[1] D.T. Tran et al., Nature Communications, 9, (2018),1594.
[2] I. Syndikus et al., Physics Letters B, 809, (2020), 135748.
[3] T. Otsuka et al. Phys. Rev. lett. 95, (2005), 232502
[4] B. Maus et al. Nucl. Instrum. Meth. Phys. Res. A 940, (2019), 01689002.
