B. J. Greenhalgh

Three-centre cluster structure in 11C and 11B

Studies of the 16O(9Be,α7Be)14C, 7Li(9Be,α7Li)5He and 7Li(9Be,ααt)5He reactions at Ebeam = 70 and 55 MeV have been performed using resonant particle spectroscopy techniques. The 11C excited states decaying into α + 7Be(gs) are observed between 8.5 and 13.5 MeV. The α + 7Li(gs), α + 7Li* (4.652 MeV) and t+8Be(gs) decays of 11B excited states between 9 and 19 MeV are observed. The decay processes are used to indicate the possible three-centre 2α + 3He (2α + 3H) cluster structure of observed states. This cluster structure is more prominent in the positive-parity states, where two rotational bands with large deformations are suggested. Excitations of some of the observed T = 1/2 resonances coincide with the energies of previously measured T = 3/2 isobaric analogues of the 11Be states, indicating that these states may have mixed isospin.

Indication for superallowed Fermi decay from the N=Z nuclei 78Y,82Nb,86Tc

The heavy odd-odd N=Z nuclei {sup 78}Y,{sup 82}Nb,{sup 86}Tc have been produced at GANIL by fragmentation of a 60 MeV/u {sup 92}Mo beam on a natural nickel target. Their lifetime have been measured for the first time, using the identification-implantation and subsequent time correlated {beta} counting technique at the LISE spectrometer. The obtained half-lives for {sup 78}Y,{sup 82}Nb,{sup 86}Tc are consistent with the microscopic predictions. These nuclei are good candidates to extend the mass range for the V{sub ud} matrix element evaluation and our experimental results highlight the interest of further investigation of their excited states and {beta} decay schemes as a function of isospin. {copyright} {ital 1998 American Institute of Physics.}

Experimental evidence for cluster structure of 11B excited states

The kinematically complete measurements of the 7Li(9Be,ααt)5He reaction at Ebeam = 55 and 70 MeV have been performed and the reconstructed 11B excitation energy spectra were compared with the 7Li(9Be,α7Li)5He results obtained at the same beam energies. Evidence was found for the t+8Be(g.s.) decay of the 11B excited states at 13.1 and 14.4 MeV, the α+7Li*(4.652 MeV) decay of the states at 14.4 and 17.5 MeV and for the t+8Be*(3.03 MeV) decay of the 17.5 MeV state in 11B. A study of the relative yields for the decay of the 14.4 MeV state indicates that significant part of α‐decay strength goes into the 2α+t three‐body decay channel.

alpha-decay of excited states in C-11 and B-11

Abstract Studies of the 16O(9Be, α7Be)14C and 7Li(9Be, α7Li)5He reactions at E beam = 70 MeV have been performed using resonant particle spectroscopy techniques. The 11C excited states decaying into α + Be 7 ( gs ) are observed at 8.65, 9.85, 10.7 and 12.1 MeV as well as possible states at 12.6 and 13.4 MeV. This result is the first observation of α-decay for excited states above 9 MeV. The α + Li 7 ( gs ) decay of 11B excited states at 9.2, 10.3, 10.55, 11.2, (11.4), 11.8, 12.5, (13.0), 13.1, (14.0), 14.35, (17.4) and (18.6) MeV is observed. The decay processes are used to indicate the possible three-centre 2 α + He 3 ( H 3 ) cluster structure of observed states. Two rotational bands corresponding to very deformed structures are suggested for the positive-parity states. Excitations of some observed T = 1 / 2 resonances coincide with the energies of T = 3 / 2 states which are the isobaric analogs of the lowest 11Be states. Some of these states may have mixed isospin.

Half-Lives of the Odd-Odd N = Z Nuclei

The heavy odd-odd nuclei , , , have been produced at GANIL by fragmentation of a beam on a natural nickel target. The species of interest were selected and identified by their energy loss in a silicon detector and their time of flight through the LISE spectrometer. The ions were implanted in a silicon strip detector in which their -decay was observed. The measured half-lives for , , correspond to superallowed transitions and may sign Fermi transitions on the basis of values. Our experimental results pave the way for further and more precise measurements of these nuclei.

^78

The study of the β decay of some N=Z nuclei in the A=70 mass range have been performed using the GANIL and CERN/ISOLDE facilities. The fast decays of three Tz=0 odd-odd nuclei have been measured for the first time which extend the number of superallowed transitions. Information has been obtained on the Gamow Teller strength distribution in the β+-EC decay of two even-even N=Z isotopes 76Sr and 72Kr. Results are compared with theoretical predictions giving indication about the shape of the ground state of the parent nucleus.

Y,

The heavy odd-odd N=Z nuclei {sup 78}Y,{sup 82}Nb,{sup 86}Tc have been produced at GANIL by fragmentation of a 60 MeV/u {sup 92}Mo beam on a natural nickel target. Their lifetime have been measured for the first time, using the identification-implantation and subsequent time correlated {beta} counting technique at the LISE spectrometer. The obtained half-lives for {sup 78}Y,{sup 82}Nb,{sup 86}Tc are consistent with the microscopic predictions. These nuclei are good candidates to extend the mass range for the V{sub ud} matrix element evaluation and our experimental results highlight the interest of further investigation of their excited states and {beta} decay schemes as a function of isospin. {copyright} {ital 1998 American Institute of Physics.}

^82

The heavy odd-odd N=Z nuclei {sup 78}Y,{sup 82}Nb,{sup 86}Tc have been produced at GANIL by fragmentation of a 60 MeV/u {sup 92}Mo beam on a natural nickel target. Their lifetime have been measured for the first time, using the identification-implantation and subsequent time correlated {beta} counting technique at the LISE spectrometer. The obtained half-lives for {sup 78}Y,{sup 82}Nb,{sup 86}Tc are consistent with the microscopic predictions. These nuclei are good candidates to extend the mass range for the V{sub ud} matrix element evaluation and our experimental results highlight the interest of further investigation of their excited states and {beta} decay schemes as a function of isospin. {copyright} {ital 1998 American Institute of Physics.}