Chemical effects of nuclear recoil

Abstract

The investigations recorded in this thesis relate to a radiochemical study of the fates of iodine atoms recoiling after undergoing radiative neutron capture. Particular attention has been focussed upon mixtures of alkyl iodides, using the 'quasi-stable' fission product (^129)I (1.72 X l0(^7) y) to fix unequivocally the origin of the recoil iodine found in the products. Techniques have been developed for the synthesis of methyl and propyl iodides labelled with (^129)I on a micro-scale, and mixtures of these with unlabelled alkyl iodides have been irradiated in the Harwell reactor "BEPO". Other irradiations have been made with 14 MeV neutrons from the D+T reaction; with a Ra-ɤ-Be neutron source; and with a 100 curie (^60)Co source. Separation (by gas/liquid chromatography) and measurement techniques have also been perfected. From a study of the distribution of the active iodine between methyl and propyl iodides it seems that the recoiling atom is more likely to appear as methyl than as propyl iodide. In the case of (^130)I recoils this, ratio is about 3:1, for (^128)I it is about 1.8:1 and for (^126)I (produced by n,2n reaction) it is about 2.2:1. The results can only be explained if it is also assumed that about 10% of the neutron captures (in (^129)I) either do not result in bond rupture or lead to an immediate recombination with the residue of the parent molecule. The effect of ɤ-radiation (unavoidably present in neutron irradiations) on the exchange of iodine between methyl and propyl iodides, has been studied with the aid of (^131)I, using a 100 curie (^60)Co source.