Detection of MeV particles from ultra-dense protium p(−1): Laser-initiated self-compression from p(1)

Ultra-dense protium p(−1) is a condensed phase of hydrogen which has a shortest H–H bond distance of 3.7 pm. It is not identical in form to ultra-dense deuterium named d(−1) or D(−1). The MeV particles released from p(−1) under impact of a ns pulsed laser are studied with time-of-flight energy measurements using a fast plastic scintillator detector. A movable metal plate or foil is used to distinguish fast particles from energetic photons. The fast particles, mainly protons, are delayed by transmission through the plate or foil from the MeV range to 200–700 keV. Fast protons are ejected only after a 5–10 s induction period after the laser start, and only at high pulse rates, approaching 10 Hz. Particles with keV energies are ejected as late as several μs after the laser pulse. Nuclear processes are excluded in the p(−1) case and the laser intensity is quite low. It is concluded that laser-triggered self-compression from p(1) to p(−1) gives the high-energy particles.