106 research outputs found

    8Li+alpha decay of 12B and its possible astrophysical implications

    Full text link
    The 12B excitation energy spectrum has been obtained from coincidence measurements of the 9Be+7Li -> 2alpha+8Li reaction at E{0}=52 MeV. The decay of the states at excitations between 10 and 16 Mev into alpha$+8Li has been observed for the first time. Observed alpha-decay indicates possible cluster structure of the 12B excited states. The influence of these states on the cross section of the astrophysically important 8Li(alpha,n)11B and 9Be+t reactions is discussed and the results are compared with existing results.Comment: accepted for publication in Europhysics Letter

    Three-centre cluster structure in 11C and 11B

    Full text link
    Studies of the 16O(9Be,alpha 7Be)14C, 7Li(9Be,alpha 7Li)5He and 7Li(9Be,alpha alpha t)5He reactions at E(beam)=70 and 55 MeV have been performed using resonant particle spectroscopy techniques. The 11C excited states decaying into alpha+7Be(gs) are observed between 8.5 and 13.5 MeV. The alpha+7Li(gs), alpha+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 2alpha+3He (2alpha+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 analogs of the 11Be states,indicating that these states may have mixed isospin.Comment: Contribution for the proceedings of the NUSTAR'05: NUclear STructure, Astrophysics and Reactions, University of Surrey, Guildford, UK; accepted for publication in Journal of Physics

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

    Full text link
    Studies of the 16O(9Be,alpha7Be)14C and 7Li(9Be,alpha7Li)5He reactions at E{beam}=70 MeV have been performed using resonant particle spectroscopy techniques. The 11C excited states decaying into alpha+7Be(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 alpha-decay for excited states above 9 MeV. The alpha+7Li(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 2alpha+3He(3H) 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.Comment: accepted for publication in Nuclear Physics

    Triaxial deformation in 10Be

    Get PDF
    The triaxial deformation in 10^{10}Be is investigated using a microscopic α+α+n+n\alpha+\alpha+n+n model. The states of two valence neutrons are classified based on the molecular-orbit (MO) model, and the π\pi-orbit is introduced about the axis connecting the two α\alpha-clusters for the description of the rotational bands. There appear two rotational bands comprised mainly of Kπ=0+K^\pi = 0^+ and Kπ=2+K^\pi = 2^+, respectively, at low excitation energy, where the two valence neutrons occupy Kπ=3/2K^\pi = 3/2^- or Kπ=1/2K^\pi = 1/2^- orbits. The triaxiality and the KK-mixing are discussed in connection to the molecular structure, particularly, to the spin-orbit splitting. The extent of the triaxial deformation is evaluated in terms of the electro-magnetic transition matrix elements (Davydov-Filippov model, Q-invariant model), and density distribution in the intrinsic frame. The obtained values turned out to be γ=15o20o\gamma = 15^o \sim 20^o.Comment: 15 pages, latex, 3 figure

    4He decay of excited states in 14C

    Full text link
    A study of the 7Li(9Be,4He 10Be)2H reaction at E{beam}=70 MeV has been performed using resonant particle spectroscopy techniques and provides the first measurements of alpha-decaying states in 14C. Excited states are observed at 14.7, 15.5, 16.4, 18.5, 19.8, 20.6, 21.4, 22.4 and 24.0 MeV. The experimental technique was able to resolve decays to the various particle bound states in 10Be, and provides evidence for the preferential decay of the high energy excited states into states in 10Be at ~6 MeV. The decay processes are used to indicate the possible cluster structure of the 14C excited states.Comment: accepted for publication in PR

    6^{6}He + α\alpha clustering in 10^{10}Be

    Full text link
    In a kinematically complete measurement of the 7^{7}Li(7^{7}Li,α\alpha6^{6}He)4^4He reaction at EiE_{i} = 8 MeV it was observed that the 10^{10}Be excited states at 9.6 and 10.2 MeV decay by 6^{6}He emission. The state at 10.2 MeV may be a member of a rotational band based on the 6.18 MeV 0+^+ state.Comment: 9 pages, RevTex, 3 Postscript figures (tarred, gzipped and uuencoded) include

    Experimental study of high-lying states in <sup>28</sup>Mg using the resonant elastic scattering of α particles

    Get PDF
    International audienceThe excitation function of Mg28 above the α-decay threshold has been measured for the first time using the resonant scattering of α particles with the technique of a thick target in inverse kinematics. Thirteen new states are reported between Ex=15.5 and Ex=20.5 MeV, and suggestions for spin-parity assignments are given for two of these. Calculations of the branching ratio to α decay for these states as well as comparison of the measured cross sections to calculations suggest that α+Neg.s.24 clustering is not dominant in this energy regime

    B(E1) Strengths from Coulomb Excitation of 11Be

    Get PDF
    The BB(E1;1/2+1/21/2^+\to1/2^-) strength for 11^{11}Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for 11^{11}Be+208^{208}Pb at 38.6 MeV/nucleon is reported. The BB(E1) strength of 0.105(12) e2^2fm2^2 derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, i n contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e2^2fm2^2. This value is in good agreement with the value deduced independently from the lifetime of the 1/21/2^- state in 11^{11}Be, and has a comparable p recision.Comment: 5 pages, 2 figures, accepted for publication in Phys. Lett.

    Helium Clustering in Neutron-Rich Be Isotopes

    Get PDF
    Measurements of the helium-cluster breakup and neutron removal cross sections for neutron-rich Be isotopes A=10-12,14 are presented. These have been studied in the 30 to 42 MeV/u energy range where reaction measurements are proposed to be sensitive to the cluster content of the ground-state wave-function. These measurements provide a comprehensive survey of the decay processes of the Be isotopes by which the valence neutrons are removed revealing the underlying alpha-alpha core-cluster structure. The measurements indicate that clustering in the Be isotopes remains important up to the drip-line nucleus 14^Be and that the dominant helium-cluster structure in the neutron-rich Be isotopes corresponds to alpha-Xn-alpha.Comment: 5 pages, 2 tables and 3 figure

    Cluster structure of 13C probed via the 7Li(9Be,13C*->9Be+alpha) reaction

    Full text link
    A study of the 7Li(9Be,4He9Be)3H reaction at E{beam}=70 MeV has been performed using resonant particle spectroscopy techniques and provides a measurement of alpha-decaying states in 13C. Excited states are observed at 12.0, 13.4, 14.1, 14.6, 15.2, 16.8, 17.9, 18.7, 21.3 and 23.9 MeV. This study provides the first measurement of the three highest energy states. Angular distribution measurements have been performed and have been employed to indicate the transferred angular momentum for the populated states. These data are compared with recent speculations of the presence of chain-like structures in 13C.Comment: accepted for publication in Nuclear Physics
    corecore