Speaker
Description
Light neutron-rich carbon isotopes provide a unique testing ground for the evolution of shell structure and halo phenomena. Specifically, we studied the single-neutron pickup $^{16}\mathrm{C}(p,d)^{15}\mathrm{C}$ and $^{16}\mathrm{C}(d,t)^{15}\mathrm{C}$, and the two-neutron pickup $^{16}\mathrm{C}(p,t)^{14}\mathrm{C}$. These complementary probes offer high sensitivity to both single-particle and pairing correlations, serving as critical benchmarks for theoretical models of transfer reactions with exotic beams.
The pickup reaction allowed us to study particle-hole configurations in $^{15}\mathrm{C}$ produced by the removal of neutrons from the $1p_{1/2}$ and $1p_{3/2}$ orbitals . The comparison of these results with different phenomenological interactions shows the sensitivity to the size of the N =8 gap and helps to constrain them [1]. In particular, $^{15}\mathrm{C}$ is a well-known one-neutron halo nucleus, with the valence neutron weakly bound ($S_n \approx 1.2$ MeV) in a $2s_{1/2}$ orbital. Its first excited state at 0.74 MeV has a dominant $1d_{5/2}$ configuration, with the transition expected to involve weak core polarization due to the inert ¹⁴C core [2]. Understanding how the halo in $^{15}\mathrm{C}$ impacts core polarization is directly relevant for understanding the quadrupole moments of $^{16}\mathrm{C}$ [2].
The experiment was performed in 2023 at the Argonne Tandem Linac Accelerator System [3] (ATLAS) using the Active Target Time Projection Chamber (AT-TPC) [4] and HELIOS solenoidal spectrometer [5,6] to study transfer reactions that selectively populate single-particle states, from which spectroscopic factors are extracted.
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contracts No. DE-AC02-06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility. This work has received financial support from the Xunta de Galicia (CIGUS Network of Research Centres) and the European Union.
References:
[1] J. Lois-Fuentes et al., EPJ Web Conf. (2023).
[2] J. Chen et al., Physical Review C 106.6 (2022): 064312.
[3] C. Hoffman, T. Tang, M. Avila, Y. Ayyad, K. Brown, J. Chen, K. Chipps, H. Jayatissa, B. Kay, C. Müller-Gatermann, H. Ong, J. Song, and G. Wilson, Nucl. Instr. Meth. Phys. Res. Sect. A 1032, 166612 (2022).
[4] J. Bradt, D. Bazin, F. Abu-Nimeh, T. Ahn, Y. Ayyad, S. Beceiro-Novo, L. Carpenter et al. Nucl. Instr. Meth. Phys. Res. Sect. A 875 (2017): 65-79.
[5] A. Wuosmaa, J. Schiffer, B. Back, C. Lister, and K. Rehm, Nucl. Instr. Meth. Phys. Res. Sect. A 580, 1290 (2007).
[6] J. Lighthall, B. Back, S. Baker, S. Freeman, H. Lee, B. Kay, S. Marley, K. Rehm, J. Rohrer, J. Schiffer, D. Shetty, A. Vann, J. Winkelbauer, and A. Wuosmaa, Nucl. Instr. Meth. Phys. Res. Sec. A 622, 97 (2010).