Calem R Hoffman

High-spin structures of holmium ( Z = 67 ) and erbium ( Z = 68 ) isotopes are presented near mass 160, a region where collective and single-particle modes of excitation compete in the generation of angular momentum at the highest experimentally attainable spins in atomic nuclei. The level schemes of the Ho 156 , 157 , 158 isotopes have been significantly extended, reaching spins in the 40 ℏ to 55 ℏ range, through multiple experiments utilizing the Gammasphere spectrometer. In particular, several new noncollective band-terminating states are reported for these nuclei. The nature of these states, including both valence-space terminations and core-excited oblateconfigurations, is discussed in terms of proton particle-hole (p-h) excitations across the semimagic Z = 64 shell closure. Cranked-Nilsson–Strutinsky (CNS) calculations have been used to interpret the nature of these noncollective states. The corresponding terminating states in Er 154 – 159 are also included, providing a systematic description of band termination in this mass region. In addition, three weak rotational structures have been assigned to Ho 157 at the highest spins. These collective bands are proposed to be based on a triaxial strongly deformed nuclear shape, involving neutron p-h excitations across the N = 82 shell gap.

In recent years there has been significant experimental effort aimed at studying the impact of O 16 neutron poisoning on the weak s process in rotating massive stars. Improving the understanding of energy levels in Ne 21 is crucial to reducing uncertainties in the rates of the α -induced reactions on O 17 that determine the overall efficiency of the weak s process. This paper reports on one such experiment: a study of the Ne 20 ( d , p ) Ne 21 reaction in inverse kinematics. Deduced spin-parity assignments were made based on adiabatic distorted-wave approximation analysis and neutron partial widths were estimated by comparison with a previous experiment. Of particular significance for nuclear astrophysics is the resulting neutron partial width for the 7820-keV energy level, estimated to be 12 200 ( 2900 ) eV , and an upper limit of ≤ 9300 eV for that of the 7749-keV energy level. These results are in tension with previous studies and therefore this paper also discusses the current state of the research into the astrophysically relevant energy levels and highlights both areas of agreement and areas of disagreement between this and various other studies that have investigated this nucleus.

This white paper is the result of a collaboration by many of those that attended a workshop at the facility for rare isotope beams (FRIB), organized by the FRIB Theory Alliance (FRIB-TA), on ‘Theoretical Justifications and Motivations for Early High-Profile FRIB Experiments’. It covers a wide range of topics related to the science that will be explored at FRIB. After a brief introduction, the sections address: section 2: Overview of theoretical methods, section 3: Experimental capabilities, section 4: Structure, section 5: Near-threshold Physics, section 6: Reaction mechanisms, section 7: Nuclear equations of state, section 8: Nuclear astrophysics, section 9: Fundamental symmetries, and section 10: Experimental design and uncertainty quantification.

Isoscalar dipole transitions are a distinctive fingerprint of cluster structures. A 1^{-} resonance at 7.27(10) MeV, located just below the α-emission threshold, has been observed in the deuteron inelastic scattering reactions off ^{10}Be. The deformation lengths of the excited states in ^{10}Be below 9 MeV have been inferred from the differential cross sections using coupled channel calculations. This observed 1^{-} resonance has isoscalar characteristics and exhausts approximately 5%-15% of the isoscalar dipole energy-weighted sum rule, providing evidence for pronounced α cluster structure in ^{10}Be. The Gamow coupled channel approach supports this interpretation and suggests the near-threshold effect might be playing an important role in this excitation energy domain. The α+α+n+n four-body calculation reproduces the observed enhanced dipole strength, implying that the four-body cluster structure is essential to describe the 1^{-} states in ^{10}Be.