Chemical effects of fission recoils. 3. Relaxation times of processes leading to ethyl radicals

Abstract

The formation of n-butane in the fission-recoil induced radiolysis of gaseous ethylene in the presence of small quantities of oxygen is interpreted by competition between radical combination in the track, radial diffusion, and radical removal by oxygen. The differential equations describing these reactions are solved and fitted to experiment by adjusting the initial mean track radius, r/sub i/, until calculations and observations agree. r/sub i/ is found to be substantially larger than the radius for physical energy deposition by primary interaction of the recoiling fission fragment or the radius within which secondary electrons (delta rays) deposit their energy. It is proposed that this is largely the result of diffusive spread of precursors to ethyl radical formation. These must survive for approximately 10/sup -9/ s before competition for second-order disappearance sets in. The functional form of the dependence of r/sub i/ on the reciprocal square root of the density is consistent with this postulate. 2 figures, 1 table.