Radioactive ion beam research at Lawrence Livermore National Laboratory

Several modifications and additions have been made to improve the radioactive beam facility at Livermore with the main aim of measuring the cross section for 7Be(pγ)8B (which is important in determining the solar neutrino flux) and other reactions of astrophysical interest. The quadrupole sextuplet spectrometer has been upgraded by inserting an electrostatic deflection element near the midpoint and by installing a movable beam stop near the 7Be production target. These changes have allowed an improvement in the purity, and large increase in the intensity, of the 7Be beam. Six large NaI(Tl) detectors and the gas cell from OSU system along with its active and passive shielding have been incorporated into the Lawrence Livermore facilty. True events are to be identified by a multiple coincidence. The first requirement is the detection of a γ-ray from the proton capture 7Be(p,γ)8B. After the candidate capture gamma is observed the 8B decay signature is required. This signature is a positron (from 8B→8Be*+e++ν) along with the two α's from 8Be→α+α observed in a CaF2 detector into whicn the 8B have implanted. Also a detector telescope inside the gas cell monitors the incoming 7Be beam. The current status of the 7Be(p,γ)8B measurement is discussed. (orig.)