Search for spontaneous position production in heavy ion-atom collisions

The experiments were conducted at GSI Darmstadt using a positron spectrometer based on the axial focussing property of a solenoidal magnetic field for charged particles together with a baffle system and an annihilation-radiation detector to provide a large detection efficiency for positrons while suppressing the gamma-ray and electron backgrounds. Two position-sensitive particle detectors determined the kinematic parameters for each collision, allowing the isolation of interesting events. The background of positrons from internal pair conversion of excited nuclear states was calculated from the gamma-ray flux monitored in NaI(Tl) detectors. The collision systems measured were U + Cm at a bombarding energy of 6.05 MeV/amu, U + U at 5.9 MeV/amu, and U + Pb at 5.9 MeV/amu