Evidence for charged-particle decay of dipole-excited {sup 4}H clusters embedded in {sup 6}He and {sup 7}He

Charged-particle decay from the dipole resonances at E{sub x}=24 MeV in {sup 6}He and at E{sub x}=18 MeV in {sup 7}He was studied via the {sup 6,7}Li({sup 7}Li,{sup 7}Be x) coincidence experiment at 455 MeV and at 0 deg. These resonances are those that were interpreted as the analogs of the dipole resonances in the {alpha} clusters of {sup 6}Li and {sup 7}Li in our previous work. The dominant decay channels (branching ratios) of the dipole resonances are found to be d+t+n (26{approx}32%) and {alpha}+2n (47{approx}69%) for {sup 6}He and t+t+n (47{approx}55%) and {alpha}+3n (38{approx}47%) for {sup 7}He. The branching ratios measured for the d+t+n and t+t+n channels in {sup 6}He and {sup 7}He, respectively, are larger than those calculated in a simple statistical model by a factor of {approx}100. These results are consistent with the picture that the observed dipole resonances are analogs of the corresponding dipole resonances in the {alpha} clusters of {sup 6}Li and {sup 7}Li.