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The study of single-particle structure in light neutron-rich systems has led to discoveries of dramatic changes which are otherwise gradual near stability, leading to the weakening and appearance of shell closures. For example, the disappearance of N = 20 and emergence of N = 16 [1, 2] as well the emergence of N = 32, 34 in calcium isotopes [3]. Pronounced trends have also been observed in stable heavier nuclei, in the changes in high-j states as high-j orbitals are filling. Studies of chains of stable, closed-shell isotopes [4] and isotones [5] have pointed to robust mechanisms for these changes, such as the importance of a tensor interaction [6].
The ISOLDE Solenoidal Spectrometer (ISS) allows studies of the single-particle properties of nuclear away from stability via measurements of single-nucleon transfer reactions, using the broad range of beams available at ISOLDE. ISS has been used to study single-particle properties of nuclei, and how they are evolving, in various regions of the nuclear chart duting it’s first physics qcampaigns.
In light neutron-rich nuclei the monopole shifts of single-particle energies with changing proton occupancies have been investigated outside N=16 with a study of states populated in $^{28}$Na, mapping out the relative behaviour of the intruder states above N=20 related to the evolution of structure here. A measurement has also been made of the fragmentation of single-particle strength in $^{31}$Mg, inside the N=20 island of inversion, where a change in ground-state structures related to the weakening N=20 shell closure occurs. Both these data can be compared to that measured previously in $^{30}$Al and $^{29}$Mg [7] to understand the systematics along N=17 and across the border of the island of inversion.
The beams available at ISOLDE allow an extension of studies of high-j orbitals to N=126, with a focus on nuclei above $^{208}$Pb, where monopole shifts arise due to the filling of the proton h$_{9/2}$ orbital. The evolution of single-neutron properties outside N=126 have been investigated, with a measurement of the $^{212}$Rn(d,p) reaction, similar in scope on previous measurements south of $^{208}$Pb in $^{207}$Hg [8].
[1] A. Ozawa et al., Phys. Rev. Lett. 84, 5493 (2000).
[2] C. R. Hoffman et al., Phys. Lett. B 672, 17 (2009).
[3] D. Steppenbeck et al., Nature 502, 207 (2013).
[4] J. P. Schiffer et al., Phys. Rev. Lett. 92, 162501 (2004).
[5] B. P. Kay et al., Phys. Lett. B 658, 216 (2008), D. K. Sharp et al., Phys. Rev. C 87, 014312 (2013).
[6] T. Otsuka et al., Phys. Rev. Lett. 95, 232502 (2005).
[7] P. T. MacGregor et al., Phys. Rev. C 104, L051301 (2021).
[8] T. L. Tang et al., Phys. Rev. Lett. 124, 062502 (2020).
This material is based upon work supported by the UK Science and Technology Facilities Council [Grants No. ST/P004598/1, No. ST/N002563/1, No. ST/M00161X/1 (Liverpool); No. ST/P004423/1 (Manchester); No. ST/P005314/1 (Surrey); the ISOL-SRS Grant (Daresbury)], and the European Union's Horizon 2020 Framework research and innovation program under grant agreement no. 654002 (ENSAR2) and the Marie Skłodowska-Curie grant agreement No. 665779 and the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357 (ANL) and the Research Foundation Flanders
| session | I. Nuclear Structure and Reactions |
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