Observation of a Peak Structure in Positron Spectra from U+Cm Collisions

Abstract

A narrow peak structure has been observed in positron spectra from U+Cm collisions at bombarding energies near the Coulomb barrier whose origin cannot be associated with established dynamic mechanisms of positron production involving Rutherford trajectories only. The peak's energy is centered at 316\ifmmode\pm\else\textpm\fi{}10 keV. Its width of \ensuremath{\sim} 80 keV, dominated by Doppler broadening, implies that the emitting system exists for longer than \ensuremath{\sim} ${10}^{\ensuremath{-}20}$ sec.