Spectroscopic Studies of Proton-Irradiated Solid Deuterium.
Spectroscopic studies were performed on solid deuterium samples while under irradiation by a 15 MeV proton beam. A vacuum ultraviolet source was developed for Lyman -alpha absorption experiments. Insufficient sample transmission prevented these experiments from being successfully performed, and a number of suggestions are made to contribute to the future success of the experiments. Preliminary tests on the feasibility of resonant harmonic generation as a probe of ground state atoms were also carried out. A broad continuous emission feature was observed in the irradiated solid. The feature was studied from 4.2 K to the melting point of D_2. Extensive study of this feature was aimed at determining the species responsible for the emission. Timing measurements showed that a small fraction of the emission persisted for many minutes after the irradiation had ceased. Laser-induced emission experiments give compelling evidence for the involvement of electrons. Lowering the sample temperature below 4.2 K resulted in the occurrence of spontaneous optical flashes where the emission intensity momentarily increased to a value 2-3 orders of magnitude greater than the steady-state value. The flash-spectrum is red shifted from that of the steady-state emission, but evidence is presented to show they share a common origin. Temperature increases similar to those reported in D-T samples (G. W. Collins et al. Phys. Rev. Lett. 65, 444, 1990) were observed by measuring the response of beam-induced infrared absorption features during a flash. Upon initial irradiation approximately 10-15 minutes elapsed between flashes. This time interval between flashes continuously decreases until a steady-state value of ~70 s is reached. The flashes are believed to be a result of rapid heating in the sample due to atomic recombination. The flashes exhibit qualitative difference from the recombination events studied in T_2 doped samples. A simple model used previously to describe thermal recombination events is examined and fails to describe a number of qualitative observations. Evidence is presented to suggest that local sample heating may be important for bulk samples. The dynamics of the flash can be used to probe the properties of unpaired atoms in the irradiated solid.
- Pub Date:
- Physics: Condensed Matter