Evidence of a Direct Process in the (He4,He8) Reaction

The transfer mechanism for the exotic (${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$) reaction has been investigated by measuring the angular distribution for the reaction ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$)${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$. The structure in the angular distribution is reproduced by a direct four-neutron-cluster transfer. In addition, the relative (${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$) cross sections from ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ are predicted correctly if collective effects are included in the spectroscopic factors.