Kinetics of Charge Scavenging in γ Irradiated Liquids with Large Free Ion Yields

Abstract

The extent to which the calculated scavenging yields are affected by the form of the ion–electron special distribution decreases as the free ion yield increases. The increasing free ion yield may be due to larger electron ranges or to a larger dielectric constant. The free ion yields in neopentane and water are respectively 1.0 (due to large electron ranges) and 2.7 (due to large dielectric constant). The scavenging yields in neopentane calculated with three different forms of spacial distribution, using the forced diffusion (FD) approximation, are significantly affected by the form of the spacial distribution. The scavenging yields in water calculated with four different forms of spacial distribution, using the FD approximation, are all within the experimental error of the measured yields. Use of the prescribed diffusion (PD) approximation permits satisfactory yields to be calculated for neopentane, but leads to the unsatisfactory result that all of the secondary electrons in the liquid have the same range (delta function distribution YD). The scavenging yield curves obtained using the PD approximation for water did not have a steep enough slope even when the distribution YD was used; YD leads to a steeper slope than any other form of distribution. The PD approximation gives an overestimate of the breadth of the geminate neutralization time distribution. The calculated time required for half of the geminate neutralization reaction to occur is similar whether the FD or PD approximation is used, but the spread of the neutralization times is an order of magnitude greater from the latter than from the former. Calculations were also done for electron scavenging in methylcyclopentane and in methanol. Methylcyclopentane behaves like cyclohexane and methanol behaves much like water with regard to the kinetics of ion–electron reactions in the spurs.