Direct Evidence for the νd5/2 Orbital in Ni69: Implications for the N=40 Island of Inversion
Abstract
Shape coexistence, a collective manifestation of nuclear structure, emerges from the underlying single-particle dynamics and is prominently observed in the region below Ni68. Theoretical studies have emphasized the key role of the νd5/2 orbital, the quadrupole partner of νg9/2, in driving deformation. However, experimental constraints on the location and properties of neutron orbitals in neutron-rich isotopes in this region remain scarce. In this Letter, the single-particle structure of Ni69 was investigated via the Ni68(d,p) reaction in inverse kinematics, performed at the ISOLDE Solenoidal Spectrometer at CERN. Several new excited states were observed, and comparisons with adiabatic distorted wave approximation (ADWA) calculations enabled ℓ-value assignments for the most strongly populated states. In particular, a state at 2.56 MeV is interpreted as the dominant fragment of the νd5/2 strength. The experimental findings are well reproduced by Large-Scale Shell Model calculations using a modified LNPS interaction with an increased νg9/2–νd5/2 energy gap. These results provide new insight into the structure of Ni69 and underscore the crucial role of the νd5/2 orbital in the onset of collectivity at the N=40 island of inversion.
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BibTeX
@article{ceulemans2026direct,
title = {{Direct Evidence for the νd5/2 Orbital in Ni69: Implications for the N=40 Island of Inversion}},
author = {A Ceulemans and R Raabe and F Nowacki and A Alharbi and H Ayatollahzadeh and S.A Bennett and F Browne and P.A Butler and A Camaiani and D Clarke and A.J Dolan and Z Eleme and C.T.A Everett and F Flavigny and S Fracassetti and S.J Freeman and L.P Gaffney and G Georgiev and S Goula and A Heinz and A Kawȩcka and J.M Keatings and M Labiche and I Lazarus and P.T Macgregor and M.V Managlia and J Ojala and B Olaizola and R.D Page and N Patronis and O Poleshchuk and A.M Sánchez-Benítez and D.K Sharp and H Törnqvist and A Youssef},
journal = {Physical Review Letters},
year = {2026},
month = oct,
doi = {10.1103/tdfs-5qzw},
url = {https://hal.science/hal-05502044v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Direct Evidence for the νd5/2 Orbital in Ni69: Implications for the N=40 Island of Inversion
AU - A Ceulemans
AU - R Raabe
AU - F Nowacki
AU - A Alharbi
AU - H Ayatollahzadeh
AU - S.A Bennett
AU - F Browne
AU - P.A Butler
AU - A Camaiani
AU - D Clarke
AU - A.J Dolan
AU - Z Eleme
AU - C.T.A Everett
AU - F Flavigny
AU - S Fracassetti
AU - S.J Freeman
AU - L.P Gaffney
AU - G Georgiev
AU - S Goula
AU - A Heinz
AU - A Kawȩcka
AU - J.M Keatings
AU - M Labiche
AU - I Lazarus
AU - P.T Macgregor
AU - M.V Managlia
AU - J Ojala
AU - B Olaizola
AU - R.D Page
AU - N Patronis
AU - O Poleshchuk
AU - A.M Sánchez-Benítez
AU - D.K Sharp
AU - H Törnqvist
AU - A Youssef
PY - 2026
DA - 2026/10/02
JO - Physical Review Letters
DO - 10.1103/tdfs-5qzw
UR - https://hal.science/hal-05502044v1
AB - Shape coexistence, a collective manifestation of nuclear structure, emerges from the underlying single-particle dynamics and is prominently observed in the region below Ni68. Theoretical studies have emphasized the key role of the νd5/2 orbital, the quadrupole partner of νg9/2, in driving deformation. However, experimental constraints on the location and properties of neutron orbitals in neutron-rich isotopes in this region remain scarce. In this Letter, the single-particle structure of Ni69 was investigated via the Ni68(d,p) reaction in inverse kinematics, performed at the ISOLDE Solenoidal Spectrometer at CERN. Several new excited states were observed, and comparisons with adiabatic distorted wave approximation (ADWA) calculations enabled ℓ-value assignments for the most strongly populated states. In particular, a state at 2.56 MeV is interpreted as the dominant fragment of the νd5/2 strength. The experimental findings are well reproduced by Large-Scale Shell Model calculations using a modified LNPS interaction with an increased νg9/2–νd5/2 energy gap. These results provide new insight into the structure of Ni69 and underscore the crucial role of the νd5/2 orbital in the onset of collectivity at the N=40 island of inversion.
SN - 0031-9007
SN - 1079-7114
ER -