Structure of the neutron-halo nucleus {sup 6}He

Journal Article · Sun Sep 01 04:00:00 EDT 1996 · Physical Review, C

DOI:https://doi.org/10.1103/PhysRevC.54.1070· OSTI ID:383319

Jaenecke, J; Annakkage, T; Berg, G P; Brown, B A; Brown, J A; Crawley, G; Danczyk, S; Fujiwara, M; Mercer, D J; Pham, K; Roberts, D A; Stasko, J; Winfield, J S; Yoo, G H ^[1]

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1. Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1120 (United States)

The {sup 6}Li({sup 7}Li,{sup 7}Be){sup 6}He charge-exchange reaction leading to the neutron-halo nucleus {sup 6}He has been studied at {ital E}({sup 7}Li) = 350 MeV. Magnetic analysis was used to observe transitions to the known {ital J}{sup {pi}} = 0{sup +} ground state and the {ital J}{sup {pi}} = 2{sup +} state at {ital E}{sub {ital x}} = 1.8 MeV as well as pronounced resonances at {approximately}5.6 MeV, {approximately}14.6 MeV, and {approximately}23.3 MeV. Coincidences with 430-keV Doppler-shifted {gamma} rays from the deexcitation in flight of the {ital J}{sup {pi}} = 1/2{sup {minus}} first-excited state in {sup 7}Be were measured to permit the identification of spin-flip transitions. All observed transitions appear to have spin-flip characteristics. The shapes of the experimental angular distributions from {theta}{sub c.m.} = 0{degree} to 18{degree} are well described by microscopic one-step finite-range distorted-wave calculations with theoretical shell-model transition amplitudes. For the two low-lying shell-model states the absolute cross sections are also well described. The internal structures of the projectile and ejectile are taken into consideration. A large number of contributions is permitted by the angular momentum couplings. Only the ground state of {sup 6}He carries significant Gamow-Teller strength {ital B}(GT). Contributions with higher {ital L} values from the central spin flip and the tensor interactions {ital V}{sub {sigma}{tau}} and {ital V}{sub {ital T}{tau}} are responsible for the mostly structureless distributions observed, and the 0{degree} cross sections are not proportional to {ital B}(GT). The strong resonances at {approximately}5.6 MeV and {approximately}14.6 MeV are interpreted as 2{sup +} and (1,2){sup {minus}} resonances, respectively, with cross sections stronger than predicted presumably due to mixing with continuum states leading to quadrupole and dipole enhancements. (Abstract Truncated)

• OSTI ID: 383319
• Journal Information: Physical Review, C, Journal Name: Physical Review, C Journal Issue: 3 Vol. 54; ISSN PRVCAN; ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ANGULAR DISTRIBUTION
ANGULAR MOMENTUM
BERYLLIUM 7
CHARGE EXCHANGE
CROSS SECTIONS
DE-EXCITATION
DIPOLES
DISTORTED WAVE THEORY
DOPPLER EFFECT
EXCITED STATES
GROUND STATES
HELIUM 6
LITHIUM 6 TARGET
LITHIUM 7 REACTIONS
MIXING
NEUTRONS
NUCLEAR HALOS
QUADRUPOLES
RESONANCE
SHELL MODELS
SPIN FLIP
TRANSITION AMPLITUDES