Low-lying level structure of the neutron-unbound N=7 isotones (original) (raw)

Structure of ^{14}B and the evolution of N=9 single-neutron isotones

Physical Review C, 2013

We have used the 13 B(d, p) 14 B reaction in inverse kinematics to study the properties of states in 14 B, the lightest particle-bound N = 9 isotone. The spectroscopic information, including spins, parities, and spectroscopic factors for the states observed in 14 B are used to deduce the wave functions for the low-lying negative parity ν(sd) levels, as well as provide information about the evolution of the effective neutron 1s 1/2 − 0d 5/2 single-particle energies. The data confirm that the ground and first-excited states are predominantly s wave in character and are single-neutron halo states. The effective single-particle energies are found to match the trends set by other N = 9 isotones.

Study of μs-isomers in neutron-rich nuclei around Z=28 and N=40 shell closures

Nuclear Physics A, 1999

A study of isomeric states in neutron -rich nuclei produced in the fragmentation -like reactions at intermediate energies are presented. Properties of the new isomers found in this work give a first experimental information on nuclear structure in a vicinity of the doubly magic nucleus 7SNi.

New Island of μs Isomers in Neutron-Rich Nuclei around the Z =28 and N =40 Shell Closures

Physical Review Letters, 1998

New isomeric states in the neutron-rich nuclei near the Z 28 and N 40 shell closures have been identified among the reaction products of a 60.3A MeV 86 Kr beam on a nat Ni target. From the measured isomeric decay properties information about the excited states and their nuclear structure has been obtained. The isomerism is related mostly to the occupation of the neutron g 9͞2 orbital, an intruder level in the N 3 fp shell. It is illustrated with the decay properties of 69 Ni m , 70 Ni m , and 71 Cu m interpreted within the nuclear shell model. [S0031-9007(98)06719-2] PACS numbers: 25.70. Mn, 21.10.Tg, 23.20.Lv, 27.50. + e The regular appearance of the nuclear isomers in the vicinity of closed shells was one of the first phenomena naturally explained by the nuclear shell model. It contributed much to the understanding of the nuclear structure in the early stage of the shell-model formulation [1], pointing out the existence of the spin-orbit term. In a standard shell-model description isomeric decay properties allow one to draw conclusions on the evolution of single particle states as well as on the residual interactions between valence nucleons .

Shell-model states with seniority ν = 3 , 5, and 7 in odd- A neutron-rich Sn isotopes

Physical Review C, 2016

Excited states with seniority ν = 3, 5, and 7 have been investigated in odd neutron-rich 119,121,123,125 Sn isotopes produced by fusion-fission of 6.9-MeV/A 48 Ca beams with 208 Pb and 238 U targets and by fission of an 238 U target bombarded with 6.7-MeV/A 64 Ni beams. Level schemes have been established up to high spin and excitation energies in excess of 6 MeV, based on multifold gamma-ray coincidence relationships measured with the Gammasphere array. In the analysis, the presence of isomers was exploited to identify gamma rays and propose transition placements using prompt and delayed coincidence techniques. Gamma decays of the known 27/2 − isomers were expanded by identifying new deexcitation paths feeding 23/2 + long-lived states and 21/2 + levels. Competing branches in the decay of 23/2 − states toward two 19/2 − levels were delineated as well. In 119 Sn, a new 23/2 + isomer was identified, while a similar 23/2 + long-lived state, proposed earlier in 121 Sn, has now been confirmed. In both cases, isomeric half-lives were determined with good precision. In the range of ν = 3 excitations, the observed transitions linking the various states enabled one to propose with confidence spin-parity assignments for all the observed states. Above the 27/2 − isomers, an elaborate structure of negative-parity levels was established reaching the (39/2 −), ν = 7 states, with tentative spin-parity assignments based on the observed deexcitation paths as well as on general yrast population arguments. In all the isotopes under investigation, strongly populated sequences of positive-parity (35/2 +), (31/2 +), and (27/2 +) states were established, feeding the 23/2 + isomers via cascades of three transitions. In the 121,123 Sn isotopes, these sequences also enabled the delineation of higher-lying levels, up to (43/2 +) states. In 123 Sn, a short half-life was determined for the (35/2 +) state. Shell-model calculations were carried out for all the odd Sn isotopes, from 129 Sn down to 119 Sn, and the results were found to reproduce the experimental level energies rather well. Nevertheless, some systematic deviations between calculated and experimental energies, especially for positive-parity states, point to the need to improve some of the two-body interactions used in calculations. The computed wave-function amplitudes provide for a fairly transparent interpretation of the observed level structures. The systematics of level energies over the broad A = 117-129 range of Sn isotopes displays a smooth decrease with mass A, and the observed regularity confirms most of the proposed spin-parity assignments. The systematics of the B(E2) reduced transition probabilities extracted for the 23/2 + and 19/2 + isomers is discussed with an emphasis on the close similarity of the observed A dependence with that of the E2 transition rates established for other ν = 2, 3, and 4 isomers in the Sn isotopic chain.

Halo Nucleus ^{11}Be: A Spectroscopic Study via Neutron Transfer

Physical Review Letters, 2012

The best examples of halo nuclei, exotic systems with a diffuse nuclear cloud surrounding a tightlybound core, are found in the light, neutron-rich region, where the halo neutrons experience only weak binding and a weak, or no, potential barrier. Modern direct reaction measurement techniques provide powerful probes of the structure of exotic nuclei. Despite more than four decades of these studies on the benchmark one-neutron halo nucleus 11 Be, the spectroscopic factors for the two bound states remain poorly constrained. In the present work, the 10 Be(d,p) reaction has been used in inverse kinematics at four beam energies to study the structure of 11 Be. The spectroscopic factors extracted using the adiabatic model, were found to be consistent across the four measurements, and were largely insensitive to the optical potential used. The extracted spectroscopic factor for a neutron in a n j = 2s 1/2 state coupled to the ground state of 10 Be is 0.71(5). For the first excited state at 0.32 MeV, a spectroscopic factor of 0.62(4) is found for the halo neutron in a 1p 1/2 state.

Isomeric levels in92Rb and the structure of neutron-rich92,94Rb isotopes

Physical Review C, 2012

The medium-spin structure of the 92 Rb nucleus, populated in spontaneous fission of 248 Cm and 252 Cf has been studied using the EUROGAM2 and the GAMMASPHERE Ge arrays, respectively. Two isomers have been found in 92 Rb at 284.2 keV and 1958.2 keV with halflives of T 1/2 = 54(3) ns and T 1/2 = 7(2) ns, respectively. A measurement of neutron-induced fission of 235 U, at the PF1B cold-neutron beam facility of ILL Grenoble has been performed to confirm the assignment of the T 1/2 = 54(3) ns, 284.2-keV isomeric level to the 92 Rb nucleus. Excited levels in 92 Rb and 94 Rb nuclei have been calculated in a large-scale shell-model framework. Isomers observed in these two nuclei have been interpreted as proton-neutron configurations involving the high-j ν1h 11/2 and π1g 9/2 orbitals.