Structure of ${}^{36}\mathrm{Ca}$ under the Coulomb Magnifying Glass

L. Lalanne (1, 2) , O. Sorlin (2) , A. Poves , M. Assié (1) , F. Hammache (1) , S. Koyama (2) , D. Suzuki , F. Flavigny (3) , V. Girard-Alcindor (2) , A. Lemasson (2) , A. Matta (3) , T. Roger (2) , D. Beaumel (1) , Y. Blumenfeld (1) , B.A. Brown , F. de Oliveira Santos (2) , F. Delaunay (3) , N. de Séréville (1) , S. Franchoo (1) , J. Gibelin (3) , J. Guillot (1) , O. Kamalou (2) , N. Kitamura , V. Lapoux (4) , B. Mauss (2) , P. Morfouace (2, 5) , M. Niikura , J. Pancin (2) , T.Y. Saito , C. Stodel (2) , J-C. Thomas (2)

1 IJCLab - Laboratoire de Physique des 2 Infinis Irène Joliot-Curie
2 GANIL - Grand Accélérateur National d'Ions Lourds
3 LPCC - Laboratoire de physique corpusculaire de Caen
4 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
5 DAM - Direction des Applications Militaires

Detailed spectroscopy of the neutron-deficient nucleus ${}^{36}\mathrm{Ca}$ was obtained up to 9 MeV using the ${}^{37}\mathrm{Ca}(p,d){}^{36}\mathrm{Ca}$ and the ${}^{38}\mathrm{Ca}(p,t){}^{36}\mathrm{Ca}$ transfer reactions. The radioactive nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce light ejectiles (the deuteron $d$ or triton $t$) that were detected in the MUST2 detector array, in coincidence with the heavy residues identified by a zero-degree detection system. Our main findings are (i) a similar shift in energy for the $1_1^{+}$ and $2_1^{+}$ states by about $-250\mathrm{keV}$, as compared with the mirror nucleus ${}^{36}\mathrm{S}$; (ii) the discovery of an intruder $0_2^{+}$ state at 2.83(13) MeV, which appears below the first $2^{+}$ state, in contradiction with the situation in ${}^{36}\mathrm{S}$; and (iii) a tentative $0_3^{+}$ state at 4.83(17) MeV, proposed to exhibit a bubble structure with two neutron vacancies in the $2s_{1/2}$ orbit. The inversion between the $0_2^{+}$ and $2_1^{+}$ states is due to the large mirror energy difference (MED) of $-516(130)\mathrm{keV}$ for the former. This feature is reproduced by shell model calculations, using the $sd\text{-}pf$ valence space, predicting an almost pure intruder nature for the $0_2^{+}$ state, with two protons (neutrons) being excited across the $Z=20$ magic closure in ${}^{36}\mathrm{Ca}$ (${}^{36}\mathrm{S}$). This mirror system has the largest MEDs ever observed, if one excludes the few cases induced by the effect of the continuum.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

L. Lalanne, O. Sorlin, A. Poves, M. Assié, F. Hammache, et al.. Structure of ${}^{36}\mathrm{Ca}$ under the Coulomb Magnifying Glass. Physical Review Letters, 2022, 129 (12), pp.122501. ⟨10.1103/PhysRevLett.129.122501⟩. ⟨hal-03531735⟩