Speaker
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Carbon isotopes provide an important platform to examine the shell closure of Z=6, which was suggested to exist in $^{14}$C due to the spin-orbital splitting of $0p_{1/2}$ and $0p_{3/2}$ [1-3]. However, it is not yet clear whether $Z=6$ closure persists in other Carbon isotopes, although there is some evidence in the proton distribution radii [1,4-7]. The first $2^+$ state in $^{16}$C was shown to be dominated by neutron excitation, but its ratio between neutron and proton quadrupole moments ($M_n/M_p$) is still not conclusive, though it has been studied by many experiments[8-13]. Questions remain about whether the second $2^+$ state is dominated by the proton or neutron excitation, and if there is a higher $2^+$ state dominated by proton excitation. In order to answer these questions, we have measured inelastic scattering reactions of the 16C nucleus on proton and deuteron with the active-target time projection chamber (AT-TPC) of Michigan State University [14] coupling to the magnetic field of HELIOS [15]. These two reactions provide two independent probes, protons and neutrons, with that have different sensitivity to protons and neutronsthe excitation of $^{16}$C. Therefore, new $M_n/M_p$ values were determined for the first $2^+$ states. A new $2^+_3$ resonance was observed at 6.1 MeV, which was found to be dominated by proton excitation. These present results seem to support the persistence of the $Z=6$ closure in $^{16}$C.
This research used resources of Argonne National Laboratory’s ATLAS facility, which is a Department of Energy Office of Science User Facility. 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 (ANL), No. DE-FG02-87ER40371(FRIB).
[1] Angeli, István, and Krassimira Petrova Marinova. "Table of experimental nuclear ground state charge radii: An update." Atomic Data and Nuclear Data Tables 99.1 (2013): 69-95.
[2] Nakamura, T., H. Sakurai, and H. Watanabe. "Exotic nuclei explored at in-flight separators." Progress in Particle and Nuclear Physics 97 (2017): 53-122.
[3] Brown, B. Alex. "The nuclear shell model towards the drip lines." Physics 47.2 (2022): 525-547.
[4] Kanungo, R., et al. "Proton Distribution Radii of 12-19C Illuminate Features of Neutron Halos." Physical Review Letters 117.10 (2016): 102501.
[5] Suzuki, Y., et al. "Parameter-free calculation of charge-changing cross sections at high energy." Physical Review C 94.1 (2016): 011602.
[6] Tran, D. T., et al. "Charge-changing cross-section measurements of 12-16C at around 45 A MeV and development of a Glauber model for incident energies 10 A–2100 A MeV." Physical Review C 94.6 (2016): 064604.
[7] Tran, D. T., et al. "Evidence for prevalent Z= 6 magic number in neutron-rich carbon isotopes." Nature communications 9.1 (2018): 1594.
[8] Imai, N., et al. "Anomalously Hindered E2 Strength B (E2;2_1^+→ 0_^+) in 16C." Physical review letters 92.6 (2004): 062501.
[9] Elekes, Z., et al. "Decoupling of valence neutrons from the core in 16C." Physics Letters B 586.1-2 (2004): 34-40.
[10] Ong, H. J., et al. "Neutron-dominant quadrupole collective motion in 16C." Physical Review C—Nuclear Physics 73.2 (2006): 024610.
[11] Ong, H. J., et al. "Lifetime measurements of first excited states in 16,18C." Physical Review C—Nuclear Physics 78.1 (2008): 014308.
[12] Wiedeking, M., et al. "Lifetime Measurement of the First Excited 2+ State in 16C." Physical review letters 100.15 (2008): 152501.
[13] Jiang, Y., et al. "Quadrupole deformation of 16C studied by proton and deuteron inelastic scattering." Physical Review C 101.2 (2020): 024601.
[14] Suzuki, D., et al. "Prototype AT-TPC: Toward a new generation active target time projection chamber for radioactive beam experiments." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 691 (2012): 39-54.
[15] Wuosmaa, A. H., et al. "A solenoidal spectrometer for reactions in inverse kinematics." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 580.3 (2007): 1290-1300.
