In an effort to understand the implications of Coulomb dissociation experiments for the determination of the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction rate, longitudinal momentum distributions of ${}^7\mathrm{Be}$ fragments produced in the Coulomb dissociation of 44 and 81 MeV/nucleon ${}^8\mathrm{B}$ beams on a Pb target were measured. These distributions are characterized by asymmetries interpreted as the result of interference between $E1\mathrm{}$ and $E2\mathrm{}$ transition amplitudes in the Coulomb breakup. When interpreted in the context of a first order perturbation theory of Coulomb dissociation that assumes a single particle ${}^8\mathrm{B}$ structure model, this measurement yields $S_{E2\mathrm{}}/S_{E1\mathrm{}}{=6.7\mathrm{}}_{-1.9\mathrm{}}^{+2.8\mathrm{}}\times {10}^{-4\mathrm{}}$ at a fragment relative kinetic energy of 0.6 MeV.

• Received 23 March 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.2209