[en] Gamma decays have been observed for the first time in the T_z = -3/2 nucleus ⁵³Ni. This represents the first gamma-spectroscopy of a T_z = -3/2 nucleus heavier than A = 33. The nucleus was produced via a two-step fragmentation process, along with its mirror ⁵³Mn. Differences in excitation energy between isobaric analogue states have been calculated and a preliminary interpretation attempted; shell model calculations are required to further understand these results. This work represents the first study of isobaric analogue states via mirrored fragmentation reactions and demonstrates the power of this new technique

[en] In stellar helium burning, ¹⁶O represents the endpoint of the helium-burning sequence due to the low rate of ¹⁶O(α,γ)²⁰Ne. We present a new direct measurement of the total capture reaction rate of ¹⁶O(α,γ)²⁰Ne at E_c.m.=2.26 MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment.

[en] Isospin-breaking effects have been studied for the first time in T=(3/2) isobaric analog states. Gamma decays have been observed from T_z=-(3/2) nuclei, ⁴⁹Fe and ⁵³Ni, presented here in new level schemes, and mirror energy differences have been computed following observation of analog states in ⁴⁹V and ⁵³Mn, respectively. Shell-model calculations in the fp shell are in good agreement with the data and reveal the importance of non-Coulomb isospin-breaking effects in T=(3/2) isobaric analog states. A two-step fragmentation process was developed to allow access to highly proton-rich nuclei and to produce each member of a mirror pair via mirrored fragmentation of a ⁵⁶Ni secondary beam. This work represents the first study using this technique and demonstrates the power of this approach for future studies of isobaric analog states in very proton-rich systems.

[en] Electron capture on neutron-rich medium-mass nuclei is a key process where the electrons that impede the collapse of the core of massive stars are captured, thereby producing very neutron-rich nuclei. As the core collapses, the supernova is then initiated. For the electron capture to proceed, however, the allowed Gamow-Teller (GT) transition must be unblocked either by thermal excitations or by mixing of proton configurations from a higher-lying shell into the ground-state configuration of the nucleus. The present paper presents an experiment performed at the National Superconducting Cyclotron Laboratory at Michigan State University, in which we study the configuration mixing in the neutron-rich⁷⁶Zn isotope. The experiment utilised single-proton and single-neutron knockout with detection of reaction-residue γ rays and measurement of the parallel momentum of the residue. Through this we investigate the proton components of the ⁷⁶Zn ground state, with a particular interest in π-g_9/2, which may unblock the GT electron capture even at low temperatures and thereby open a new pathway for the initiation of the collapse of the pre-supernova stellar core.

[en] Excited states in the N=Z-2 nucleus ⁴⁴V have been observed for the first time. The states have been identified through particle-γ-γ coincidence relationships and comparison with analog states in the mirror nucleus ⁴⁴Sc. Mirror energy differences have been extracted and compared to state-of-the-art shell-model calculations which include charge-symmetry-breaking forces. Observed decay pattern asymmetries between the mirror pair are discussed in terms of core excitations, electromagnetic spin-orbit effects and isospin mixing.

[en] Excited states have been observed in the N=Z-2 odd-odd nucleus ⁴⁸Mn for the first time. Through comparison with the structure of ⁴⁸V, a first high-spin study of an odd-odd mirror pair has been achieved. Differences between the T=1 analogue states in this pair have been interpreted in terms of Coulomb effects, with the aid of shell-model calculations in the full pf valence space. Unlike other mirror pairs, the energy differences have been interpreted almost entirely as due to a monopole effect associated with smooth changes in radius (or deformation) as a function of angular momentum. In addition, the large energy shift between analogue negative-parity states is interpreted in terms of the electromagnetic spin-orbit interaction in nuclei