Dissociation of ^8He(Coulomb dissociation,IAS,SHE)

抄録

We have performed kinematically complete measurements of Coulomb dissociation of 24A MeV ^8He into ^6He and two neutrons. Momenta of incident beam particles and outgoing decay products from the ^8He dissociation were measured in coincidence. The two neutron removal cross sections were extracted from inclusive (^6He+n+X) and exclusive (^6He+2n) data sets. The cross sections from the two data sets differ by a factor of two. This discrepancy can be understood with an assumption of the sequential decay property in the ^8He dissociation. This assumption was further verified with the relative energy distribution of the ^6He+n system. The excitation energy of the ^8He can be reconstructed. The excitation spectrum for a Pb target shows broad structure indicating the E1 continuum state as observed in measurements of the other halo nuclei. The photonuclear cross section σ_<E1> and the dipole strength function dB(E1)/dE_d were deduced for the first time.