Isovector giant resonances in 6He, 12B, 90Y, 120In, and 208Tl observed in the (7Li,7Be) charge-exchange reaction

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Abstract

The (7Li,7Be) and (7Li,7Beγ) reactions have been studied at bombarding energies of 50 A MeV on targets of 6Li, 12C, 90Zr, 120Sn, 208Pb, and polystyrene. The detection of Doppler-shifted γ-rays from excited 7Be permits the identification of the spinflip and non-spinflip characteristics. Transitions to over 20 discrete states and resonances have been observed. Angular distributions for 6Li and 12C are well described by microscopic one-step distorted-waves calculations with shell-model transition amplitudes. The transitions to the ground states of 6He and 12C exhibit significant Gamow-Teller strength, but ∼7% and ∼17%, respectively, of the calculated cross sections at θ ≈ 0° arise from the tensor interaction. A broad resonance at ∼5.6 MeV in the halo nucleus 6He with Jπ = (2+,1,0+) seems to correspond to a structure predicted at this excitation energy containing soft modes of excitation with Jπ = 0+and/or 2+. A resonance in 12B at ∼4.5 MeV is described by a superposition of known 2 and 4 states, and another one at ∼7.5 MeV is dominated by a transition to a 2 state with weaker contributions from two 1 states (spin dipole and giant dipole). Four to six resonances each, mostly spin-dipole resonances, were identified in the final nuclei 90Y, 120In, and 208Tl. The non-resonant quasi-free charge-exchange reaction pbound(7Li,7Be)nfree was observed for all targets up to effective excitation energies of 50 MeV. The mechanism is related to that on free protons. The effective number of participating protons was determined.

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  • Cited by (0)

    1

    Present address: Balmoral, Auckland 1000, New Zealand.

    2

    Present address: Department of Physics, University of Surrey, Guildford, Surrey GU2 5XH, UK.

    3

    Present address: Department of Physics, Millikin University, Decatur, IL 62522, USA.

    4

    Present address: College of Science and Mathematics, University of South, Carolina, Columbia, SC 29208, USA.

    5

    Present address: Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, USA.

    6

    Present address: Nuclear Physics Laboratory, University of Colorado, Boulder, CO 80309, USA.

    7

    Present address: Lockheed Martin, M&DS, Valley Forge, PA 19101, USA.

    8

    Present address: Ford Research Laboratory, MD3429, 2000 Rotunda Drive, Dearborn, MI 48121, USA.

    9

    Present address: Department of Physics, Dae Bull Institute of Science and Technology, Seoul, South Lorea.

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