Scavenging of "dry" electrons prior to hydration by azide ions: Effect on the formation of H2 in the radiolysis of water by 60Co γ-rays and tritium β-electrons.

In this study, we use Monte Carlo track chemistry simulations to show that "dry" secondary electrons, precursors of the "hydrated" electron (e^-_aq), can be scavenged on the sub-picosecond time scale prior to hydration, by a high concentration (>0.1-1 M) of azide ions (N₃^-) in water irradiated with ⁶⁰Co γ-rays and ³H β-electrons at 25 °C. This is a striking result, as N₃^- is known to react very slowly with e^-_aq. These processes tend to significantly reduce the yields of H₂ as observed experimentally. For both energetic Compton electrons ("linear energy transfer", LET ∼ 0.3 keV/μm), which are generated by the cobalt-60 γ-rays, and ³H β-electrons (LET ∼ 6 keV/μm), our H₂ yield results confirm previous Monte Carlo simulations, which indicated the necessity of including the capture of the precursors to e^-_aq. Interestingly, our calculations show no significant changes in the scavenging of "dry" electrons at high azide concentrations in passing from γ-radiolysis to tritium β-radiolysis (<i>i.e.</i>, with LET). This led us to the conclusion that the higher H₂ yield observed experimentally for ³H β-electrons compared to ⁶⁰Co γ-rays is explained mainly by the difference in the radiation track structures during the chemical stage (>1 ps). The higher LET of tritium β-electrons leads to more molecular products (H₂ in this case) in tritium radiolysis than in γ-radiolysis. Finally, a value of 0.5 nm was derived for the reaction distance between N₃^- and the “dry” electron from the H₂ yields observed in ⁶⁰Co γ-radiolysis at high N₃^- concentrations.

MeV particles in a decay chain process from laser-induced processes in ultra-dense deuterium D(0)

The ejection of particles with energy up to 20 MeV u-1 was reported previously from laser-induced processes in ultra-dense deuterium D(0). Studies of the kinetics of particle formation and decay, and of particle penetration through thick plates are now reported. Magnetic deflection is used to remove charged particles like electrons formed at the target. The signals at a collector in the beam at 0.9 m distance and a shadowed loop collector behind a 1.5–4.5 mm thick steel plate at 0.6 m are compared. The signal at the distant collector matches an intermediate particle B in a decay chain A → B → C with formation and decay time constants of 5–15 ns. The signal at the loop collector is delayed relative to the more distant collector, thus showing a delay of the particles penetrating through the steel plate. The signal at this collector is due to pair production with charge cancellation. Compton electrons from gamma radiation are observed at peak current densities of 1 mA cm-2 at the distant collector.