The radiation chemistry of aqueous solutions - I. The effect of changing linear energy transfer along a polonium α -particle track

Abstract

Absolute G values for chemical change when various aqueous solutions are irradiated with α -particles from an external polonium source have been determined for different fractions ( x ) of the α -particle track spent within the solution. G(Fe 3+ ) for an aerated solution containing 1 mM ferrous ions and 0.1N sulphuric acid decreases from 5.0 at x =0.02 through a minimum value 3.65 at 0.11 x 0.01 and then increases to 5.94 at x = 0.525. The local value G(Fe 3+ ), defined as G(Fe 3+ ) for an element of track length a distance x R from the end of the track, where R is the range of the whole track in water, shows a similar but more pronounced dependence on x which is strongly reminiscent of the inverted Bragg curve for l. e. t. plotted against x in this medium, having a minimum of 3.2 5 ± 0.1 5 at x= 0.085±0.015. As x is increased G(Ce 3+ ) for an aerated 200 μM solution of ceric sulphate in 0.1 N sulphuric acid shows no minimum but increases from 1.0 at x =0.04 to 3.0 at x=0.25 and 4. 05 at x = 0.525. Thallous ions have no effect on G(Ce 3+ ) for x ≤ 0.45. G(H 2 O 2 ) for aerated water was found to be 1.22 ±0.06. It is concluded that very few hydroxyl radicals are available and that the intra-track reactions between H 2 O 2 and H as well as OH are very important and vary in extent as x is varied.