High Dose Rate Radiolysis of n-Pentane, n-Hexane, and Their Mixtures

Author

Shen-Shong Sam Huang

Date of Award

4-1975

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Paul Y. Feng

Second Advisor

Myran C. Sauer

Third Advisor

Kazuo Nakamoto

Fourth Advisor

Raymond E. Bournique

Fifth Advisor

Michael A. McKinney

Abstract

The radiolysis of pure liquid n-pentane, n-hexane and
n-pentane/n-hexane mixtures have been studied at dose rates up to 1.2 x 10²⁸ eV 1.^-1 sec ^-1 (- 10¹⁵ rads hr ^-1) . Both the absolute yields of many of the radiolysis products and their relative distribution were found to be appreciably affected by dose rate. The gamma and high-dose rate 100-eV yields of hydrogen, G(H₂), for example, equalled respectively 5.5 and 4.2 in the case of n-hexane radiolysis and 5. 0 and 3.5 in the case of n-pentane radiolysis. The corresponding yields of the dimeric products are, similarly, for G(C1₂H26) (hexane experiments), 1.8 and 1.1; and for G(C₁₀H22 (pentane experiments), 2.2 and 1.3. In addition, the distribution of the products 1s also seen to be a function of dose rate, e.g., the relative yields of the six isomeric dodecanes (n-dodecane, 5-methylundecane, 4 -ethyldecane, 5,6 - dimethyldecane, 4-ethyl-5-methylnonane and 4,5-diethyloctane ) was found to change from 0.11 : 0.44 : 0.31 : 1.0 : 1.46 : 0.63 (gamma experiments) to 0.22 (high dose rate experiments). 1.33 : 1.0 : 1.0 : 1.67 : 0.95

Kinetic analysis of our experimental results showed that the reactions principally responsible for the observed dependence on the dos~ rate are the reactions between the hydrogen atoms and the alkyl radicals, the intercombination of the alkyl radicals, and at the highest dose rates, the combination of the hydrogen atoms. Good agreements are obtained between calculated and experimental results using the following rate constants (in 1. mole^-1 sec^-1) : ^k(H + H) = 1.0 x 10^{10 k}(H + alkyl) = ~.5 X 10^{9 k}(H + alkyl) 5.0 x 10⁹, ^k(alkyl + alkyl)=5.0 x 10⁹, ^k(hexyl + hexyl) = 3.1 x 10⁹, ^k(pentyl + pentyl) = 4.7 x 10⁹, ^k(H + hexane) = 4.9 x 10⁶, ^k(H+pentane = 3.8 x 10⁶, ^k(CH3 + hexane = 1.2 x 10², and ^k(CH3 + pentane = 1.0 x 10².

Even at the high dose rates used in our experiment, our analysis also showed that the product yields should approach asymptotically those observed in gamma radiolysis experiments if the pulse lengths are shortened - a conclusion which was indeed borne out by our experimental studies with pulse lengths ranging from 0.2 to 5.5 microseconds.