Revision 1

Accepted · first revision · record

Title: Inter-track radical recombination rates at FLASH dose rates
Plain: At very high dose rates the chemical fragments made by different particle tracks overlap and can react with each other before reaching biological targets. The size of this effect is unknown.
Precise: Determine the yields of hydroperoxyl, peroxyl and organic radicals, and of hydrogen peroxide, as a function of instantaneous dose rate from $100\ \text{to}\ 10^{9}\,\mathrm{rad}/\mathrm{s}$ in oxygenated aqueous and lipid-containing media, including inter-track overlap. Required inputs: second-order rate constants, radical diffusion lengths and the spatial density of tracks at a given dose per pulse. An answer is measured and computed yield curves $G(\text{dose rate})$ accurate to about 10 percent.
Settled by: Pulse-radiolysis and chemical-probe measurements of radical and peroxide yields spanning the dose-rate range, matched by stochastic track-chemistry simulation.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: open
Status note: Measurements of reduced peroxide yield at ultra-high dose rate exist but do not yet constrain the biologically relevant organic radical channels.
Posed since: 2020