Extension of a spur overlap model for the radiolysis of water to include high linear energy transfer regions

Results are presented from computer calculations based upon an improved diffusion-kinetic model of the spur which includes a novel initial distribution for the hydrated electron, an approximate mathematical treatment of the spherically symmetrical overlap of spurs, and a high linear energy transfer (LET) component. The results of such calculations for various conditions of pulse dose and concentrations of scavengers of individual primary chemical species in the spur are compared with experimental data obtained from water and aqueous solutions irradiated with 10-15 MeV electron pulses. Very good agreement between calculated and experimental hydrated electron decay kinetics in pure water was observed earlier at high pulse dose. However, the calculated and experimental curves are observed to deviate for times greater than 10 ns when low pulses doses and low scavenger concentrations are considered. This deviation in experimental and calculated hydrated electron decay cannot be explained by assuming the presence of a hydrated electron scavenging impurity or by employing a random distribution of nearest-neighbor interspur distances to refine the overlap approximation. However, calculations which model a constant percentage of the total energy deposition in high spur density (high-LET) regions are shown to produce good agreement with pure-water data over the entire time rangemore » studied for all pulse-dose values considered. These results provide support for theories proposing the formation of a significant number of high-LET regions in water irradizated with electrons generally characterized as being of low LET.« less