Water radiolysis with heavy-ion beams at GANIL. Back to 20 years of investigations

G Baldacchino

doi:10.1088/1742-6596/629/1/012009

Abstract

This article reports a short history of the studies carried out in the domain of radiation chemistry with the swift heavy ions of GANIL (Grand Accélérateur National d'lons Lourds) during the last 20 years. The originality of these studies lays on two main aspects which were never been investigated simultaneously before: 1) the energy of the GANIL ions provides an energy deposition in small samples (few millimeters) that can be considered as almost constant; this allows studies on LET-effect on radiolytic yields, 2) production of pulses as short as a few nanoseconds made available the access to pulse radiolysis method and the study of transient chemical species such as hydrated electron, hydroxyl radical and superoxide. Future is now focus on high temperature effects on water radiolysis for which, again, nothing exist but only simulations and speculations.

Highlights

To depict the effects of LET on the radiolysis of liquid water the use of heavy ion beams of various energies, charges and types are necessary to determine the spatial distribution of the deposited energy, the fate of the deposited energy and the time-dependence of the diffusion and reaction processes
The current knowledge in radiation chemistry with high LET particles, and it was many times verified, is that radiolytic yields of the molecular products (H2 and H2O2) increase with the LET whilst those for the radical species decrease. This general tendency is a result of a more efficient recombination of the radical species to form molecular species in the tracks since the density of the ionisation events is greater with high LET particles
[5-8] which is based on concentration measurements of a final stable product of reactions. In this method the time dependence of the radiolytic yields is determined from the concentration and the rate constant of the reaction between the scavenger and the radical species

Summary

Context - A brief history of the heavy ion water radiolysis studies

As an introduction of the radiation chemistry investigations initiated at GANIL, we must depict the crucial issues in this domain. These aspects have been deduced mainly from the studies involving the chemical scavenging method [5-8] which is based on concentration measurements of a final stable product of reactions In this method the time dependence of the radiolytic yields is determined from the concentration and the rate constant of the reaction between the scavenger and the radical species. Many details of this experiments are collected in a recent short review on pulse radiolysis with heavy ions [15]. It concerned the production of stable products such as hydrogen peroxide (H2O2) or molecular hydrogen (H2) In this short review we will focus essentially on the transient species studied by pulse radiolysis technique coupled to the high-energy ions at GANIL during the last 20 years

Review of the main results by pulse radiolysis

Hydroxyl radical

Superoxide radical

Future