Search Results (8 total)

The neutron rich nuclei ^61,63Co have been studied using the reactions ¹⁶O(⁴⁸Ca,p2n)⁶¹Co and ¹⁸O(⁴⁸Ca,p2n)⁶³Co at a bombarding energy of 110 MeV. Discrete γ rays from the channels of interest were investigated using prescaled γ singles, charged-particle–γ, neutron–charged-particle–γ, and charged-particle–γ–γ coincidence techniques. Decay schemes, with level spins deduced from two-point angular distribution data, are presented together with some approximate information on apparent state lifetimes. The experimental results are compared with previous light ion data for these systems and with theoretical shell model predictions. These data represent the first study of medium to high spin states in these nuclei. © 1996 The American Physical Society.

Isomeric transitions in ⁶⁹Se are investigated using charged particle-γ and γ-γ delayed coincidence measurements. A precise three-point angular distribution shows that the decay of the 9/2⁺ isomer is nearly isotropic, suggesting either significant dealignment during the lifetime of the isomer or a small E3 admixture in this transition. An improved measurement of the lifetime of the isomer yields a half-life of 960±23 ns. The single particle level structure of negative parity states in ⁶⁹Se below the 9/2⁺ isomer is investigated using a recoil shadowing technique. A 39.4 keV gamma ray with a total-internal conversion coefficient of 28.0±2.5 is observed deexciting the 5/2^- first excited state, which is found to be isomeric with a half-life of 2.0±0.2 μs. The observed lifetime, along with the internal conversion coefficient, suggests E2 multipolarity for this transition and strongly favors a spin and parity assignment of 1/2^- for the ⁶⁹Se ground state.

We have investigated correlations between evaporated protons and discrete γ rays in the heavy-ion fusion-evaporation reactions ⁵⁸Ni(²⁷Al,3p)⁸²Sr and ⁵⁸Ni(²⁸Si,4p)⁸²Sr. 3p-γ and 4p-γ coincidences were measured using a 4π charged-particle detector array. The events studied were completely reconstructed kinematically in order to determine the excitation energy of formation of ⁸²Sr. Correlations arising from well-understood kinematic effects were measured and found to be well reproduced by predictions made by the statistical-model evaporation code pace2. Dynamical correlations due to nuclear structure effects were searched for by measuring proton spectra in coincidence with discrete γ rays from four rotational bands in ⁸²Sr. Contrary to published results, no significant shifts of the first moment of the spectra were observed.

The structure of the neutron-rich (T_z=3) nucleus ⁴⁰Cl is investigated by measuring α-p-γ-γ and α-p-n-γ-γ coincidences using the heavy-ion fusion-evaporation reaction ⁹Be(³²S,αp)⁴⁰Cl. A total of 18 in-beam transitions in ⁴⁰Cl are identified and a level scheme is constructed up to spin (8^-) and 4.087 MeV excitation energy. The experimental results are discussed in the context of previous work and compared to shell-model predictions. Excitation energies of the negative parity yrast states and relative electromagnetic transition strengths obtained from calculations based on the full (2s,1d)²¹(1f2p)³ configuration space are in good agreement with the experimental results.

A total of ten previously observed γ rays have been assigned to the N=Z+1 nucleus ⁶³Ga; these provide the first information on excited states reported in this neutron-deficient system. ⁶³Ga has been populated using the ⁴⁰Ca(²⁸Si, αp), ⁴⁰Ca(³²S, 2αp), and ⁴⁰Ca(²⁹Si, αpn) reactions at beam energies of 80–100 MeV. Particle-γ coincidence techniques provide a definitive identification of γ transitions in ⁶³Ga. An yrast-level scheme is proposed on the basis of charged-particle-γ, charged-particle-γ-γ, and neutron-γ-γ coincidences. Spin and parity assignments are based on neutron-gated γ-ray angular distributions, directional correlation with oriented nuclei ratios and systematics. Nine new energy levels are identified in addition to the previously known ground state, with the highest level at an excitation energy of 7.7 MeV. The results are interpreted in terms of the relevant single-particle orbitals and the systematics of the neighboring nuclei. In addition, a new determination has been made of the E2/M1 mixing ratio for the (5/2^-)₁→(3/2^-)₁ transition in ⁶⁵Ga, resolving a disagreement between two previous measurements.

Charged-particle-γ and charged-particle-neutron-γ coincidences have been used to identify in-beam γ-ray transitions in ⁶⁹Se produced in the reaction ⁴⁰Ca(³²S,2pn)⁶⁹Se. Charged-particle-γ-γ coincidences, neutron-γ-γ coincidences, and neutron-gated γ-ray angular distributions were used to deduce the level scheme. A long-lived isomer attributed to the g_9/2 state was found; its half-life was measured with charged-particle-γ timing as 1023±110 ns. The presence of strong ΔJ=1 and ΔJ=2 transitions in the band built on the νg_9/2 neutron single-particle state and the measured sign of the E2/M1 mixing ratio for the (11/2⁺→(9/2⁺ transition are consistent with a theoretically predicted oblate shape for this nucleus.

Two rotational band structures have been identified in doubly odd ¹³⁰Pr following the ¹¹⁰Cd(²⁸Si,αp3n)¹³⁰Pr reaction. One band, having no signature splitting, is believed to be built on the near-prolate πh_11/2⊗νg_7/2 configuration. A second band, with a small signature splitting, is built on the triaxial πh_11/2⊗νh_11/2 configuration. Systematics of recent results for the doubly odd ¹³⁰,132,134Pr isotopes are presented.

The structure of the very neutron-deficient Ge region has been investigated with use of particle-γ coincidence techniques in weak fusion-evaporation channels. Excited states up to spin (31/2) have been established in ⁶⁵Ge, and five transitions have been assigned to the N=Z nucleus ⁶⁴Ge. The first excited state in ⁶⁴Ge is at 902.1±0.8 keV. The ⁶⁵Ge level scheme provides the first indication in this mass region of a theoretically predicted softness with respect to octupole deformation.