Dr Laetitia Canete

Two long-standing puzzles in the decay of ¹⁸⁵Bi, the heaviest known proton-emitting nucleus are revisited. These are the nonobservation of the 9/2(-) state, which is the ground state of all heavier odd-A Bi isotopes, and the hindered nature of proton and alpha decays of its presumed 60-mu s 1/2(+) ground state. The ¹⁸⁵Bi nucleus has now been studied with the ⁹⁵Mo(⁹³Nb, 3n) reaction in complementary experiments using the Fragment Mass Analyzer and Argonne Gas-Filled Analyzer at Argonne National Laboratory's ATLAS facility. The experiments have established the existence of two states in ¹⁸⁵Bi; the short-lived T-1/2 = 2.8(-1.0)(+2.3) mu s, proton- and alpha-decaying ground state, and a 58(2)-mu s gamma-decaying isomer, the half-life of which was previously attributed to the ground state. The reassignment of the ground-state lifetime results in a proton-decay spectroscopic factor close to unity and represents the only known example of a ground-state proton decay to a daughter nucleus (¹⁸⁴Pb) with a major shell closure. The data also demonstrate that the ordering of low- and high-spin states in ¹⁸⁵Bi is reversed relative to the heavier odd-A Bi isotopes, with the intruder-based 1/2(+) configuration becoming the ground, similar to the lightest At nuclides.

The astrophysical 25Al(p,γ) 26Si reaction represents one of the key remaining uncertainties in accurately modeling the abundance of radiogenic 26Al ejected from classical novae. Specifically, the strengths of key proton-unbound resonances in 26Si, that govern the rate of the 25Al(p,γ) reaction under explosive astrophysical conditions, remain unsettled. Here, we present a detailed spectroscopy study of the 26Si mirror nucleus 26Mg. We have measured the lifetime of the 3+, 6.125-MeV state in 26Mg to be 19(3) fs and provide compelling evidence for the existence of a 1– state in the T = 1, A = 26 system, indicating a previously unaccounted for ℓ = 1 resonance in the 25Al(p,γ) reaction. Using the presently measured lifetime, together with the assumption that the likely 1– state corresponds to a resonance in the 25Al + p system at 435.7(53) keV, we find considerable differences in the 25Al(p,γ) reaction rate compared to previous works. Furthermore, based on current nova models, we estimate that classical novae may be responsible for up to ≈ 15% of the observed galactic abundance of 26Al.

Isomeric states in 128In and 130In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. By employing state-of-the-art ion manipulation techniques, three different beta-decaying states in 128In and 130In have been separated and their masses measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spectroscopy station. A new beta-decaying high-spin isomer feeding the isomer in 128Sn has been discovered in 128In at 1797.6(20) keV. Shell-model calculations employing a CD-Bonn potential re-normalized with the perturbative G-matrix approach suggest this new isomer to be a 16⁺ spin-trap isomer. In 130In, the lowest-lying (10⁻) isomeric state at 58.6(82) keV was resolved for the first time using the phase-imaging ion cyclotron resonance technique. The energy difference between the 10⁻ and 1⁻ states in 130In, stemming from parallel/antiparallel coupling of (π0g-19/2) ⊗ (v0h-111/2), has been found to be around 200 keV lower than predicted by the shell model. Precise information on the energies of the excited states determined in this work is crucial for producing new improved effective interactions for the nuclear shell model description of nuclei near 132Sn.