Isospin symmetry breaking at high spin in the mirror nucleiAr35andCl35

Abstract

High-spin states in 35 Ar and 35 Cl have been populated in the 24 Mg( 16 O, αn) and 24 Mg( 16 O, αp) reactions, respectively, at a beam energy of 70 MeV. The comparison between the level schemes of these mirror nuclei shows a striking asymmetry in the population yield of high-spin analog states of positive parity, which indicates different intensities of E1 transitions connecting positive-and negative-parity structures in both nuclei. Large energy differences are observed between analog states of negative parity with configurations of dominant pure single-particle character. This results from the comparison with large-scale shell-model calculations in the s 1/2 d 3/2 f 7/2 p 3/2 valence space. It is shown that important contributions to the energy differences arise from the multipole Coulomb and the relativistic electromagnetic spin-orbit interactions.

Superdeformation andα-cluster structure in35Cl

“…In our earlier work [15], we have discussed about a few totally shifted gamma rays in the spectra emitted from states having lifetimes shorter than the characteristic stopping time (≃ 10 −13 s) of 35 Cl recoils in gold (Au) backing. Analysis of the present data confirmed [16] that four of them (2912 keV, 1862 keV, 2391 keV and 3734 keV) belong to the same sequence (marked as SD in Fig. 1), which is connected to the other states in 35 Cl through 1113, 1336, 2232 and 1693 keV transitions ( Fig.…”

“…The SDPF.SM [1][2][3] Hamiltonian suitable for fixed nhω [3] excitation has also been used. The valence space consists of full sd − pf orbitals for both protons and neutrons above the 16 O inert core (see Ref. [15] for details).…”

“…and strong cross-over E2 transitions, follow a linear relation to the I(I+1) values providing a strong evidence in favour of cluster structure of these states. Results of LBSM calculations have shown that the SD band has been generated by 3p-3h excitations ((sd) 16 (pf ) 3 configuration). A simple two level mixing calculation has been done to extract the wavefunction structure of these mixed states from the experimental B(E2) values.…”

Understanding nuclei in the upper sd - shell

“…It is well known that a complementary way to test isospin symmetry is based on investigation of the electromagnetic decay properties in mirror pairs. Anomalous MED in sd shell nuclei, 35 Cl and 35 Ar has been observed [4]. In the present effort, we have done measurements of the lifetimes of excited higher spin levels of 35 Cl, mixing ratios of a few gamma transitions in 35 Ar and determined polarisation asymmetry of some gamma rays (Fig.…”

“…Superdeformation (SD) in 40 Ca [2] and 36 Ar [3] have been reported. Strong violation of isospin symmetry observed in mirror pairs has been an issue of serious discussion [4]. The nuclei in the neighbourhood of doubly closed 40 Ca are usually suitable for applications of spherical shell model calculations.…”