| 1. |
- Browne, F., et al.
(author)
-
Pairing Forces Govern Population of Doubly Magic Ca-54 from Direct Reactions
- 2021
-
In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 126:25
-
Journal article (peer-reviewed)abstract
- Direct proton-knockout reactions of Sc-55 at similar to 220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of Ca-54 were investigated through -ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological intemucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors, which describe the wave function overlap of the Sc-55 ground state with states in Ca-54. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of Sc-55, valence proton removals populated predominantly the ground state of Ca-54. This counterintuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.
|
|
| 2. |
- Fernández, A., et al.
(author)
-
Mirror energy differences above the 0f7/2 shell: First γ-ray spectroscopy of the Tz=−2 nucleus 56Zn
- 2021
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 823
-
Journal article (peer-reviewed)abstract
- Excited states in 56Zn were populated following one-neutron removal from a 57Zn beam impinging on a Be target at intermediate energies in an experiment conducted at the Radioactive Isotope Beam Factory at RIKEN. Three γ rays were observed and tentatively assigned to the 6+ → 4+ → 2+ → 0+ yrast sequence. This turns 56Zn into the heaviest Tz=−2 nucleus in which excited states are known. The excitation-energy differences between these levels and the isobaric analogue states in the Tz=+2 mirror partner, 56Fe, are compared with large-scale shell-model calculations considering the full pf valence space and various isospin-breaking contributions. This comparison, together with an analysis of the mirror energy differences in the A=58, Tz=±1 pair 58Zn and 58Ni, provides valuable information with respect to the size of the monopole radial and the isovector multipole isospin-breaking terms in the region above doubly-magic 56Ni.
|
|
| 3. |
- Jungclaus, A., et al.
(author)
-
Position of the single-particle 3/2− state in 135Sn and the N=90 subshell closure
- 2024
-
In: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 851
-
Journal article (peer-reviewed)abstract
- The decay of excited states of the nucleus 135Sn, with three neutrons outside the doubly-magic 132Sn core, was studied in an experiment performed at the Radioactive Isotope Beam Factory at RIKEN. Several γ rays emitted from excited 135Sn ions were observed following one-neutron and one-neutron-one-proton removal from 136Sn and 137Sb beams, respectively, on a beryllium target at relativistic energies. Based on the analogy to 133Sn populated via one-neutron removal from 134Sn, an excitation energy of 695(15) keV is assigned to the 3/2− state with strongest single-particle character in 135Sn. This result provides the first direct information about the evolution of the neutron shell structure beyond N=82 and thus allows for a crucial test of shell-model calculations in this region. The experimental findings are in full agreement with calculations performed employing microscopic effective two-body interactions derived from CD-Bonn and N3LO nucleon-nucleon potentials, which do not predict a pronounced subshell gap at neutron number N=90. The occurrence of such a gap in 140Sn, i.e., when the 1f7/2 orbital is completely filled, had been proposed in the past, in analogy to the magicity of 48Ca, featuring a completely filled 0f7/2 orbital one harmonic oscillator shell below.
|
|
| 4. |
- Koiwai, T., et al.
(author)
-
A first glimpse at the shell structure beyond Ca-54 : Spectroscopy of K-55, Ca-55, and Ca-57
- 2022
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 827, s. 136953-
-
Journal article (peer-reviewed)abstract
- States in the N = 35 and 37 isotopes Ca-55,Ca-57 have been populated by direct proton-induced nucleon removal reactions from Sc-56,Sc-58 and Ca-56 beams at the RIBF. In addition, the (p, 2p) quasi-free single-proton removal reaction from Ca-56 was studied. Excited states in K-55, Ca-55, and Ca-57 were established for the first time via in-beam gamma-ray spectroscopy. Results for the proton and neutron removal reactions from Ca-56 to states in K-55 and Ca-55 for the level energies, excited state lifetimes, and exclusive cross sections agree well with state-of-the-art theoretical calculations using different approaches. The observation of a short-lived state in Ca-57 suggests a transition in the calcium isotopic chain from single-particle dominated states at N = 35 to collective excitations at N = 37.
|
|
