Heavy-Ion Radiolysis of Cyclooctane

Abstract

The major products produced in radiolysis of cyclooctane with 1-15 MeV protons, 10-30 MeV carbon ions, and 20-30 MeV oxygen ions were investigated in the absence and presence of iodine radical scavenger and compared with the y and 5-20 MeV helium ion radiolysis published in a previous work (J. Phys. Chem. 1994, 98, 8014). While almost 70% of the cyclooctyl radicals survive until a few microseconds in y-radiolysis, the yields with carbon ions and oxygen ions are about an order of magnitude lower. It appears that all of the hydrogen atoms produced in y-radiolysis react by hydrogen atom abstraction from the medium molecules, whereas in the heavy-ion tracks enhanced intratrack reactions eliminate most of the hydrogen atoms before such reactions can occur to any significant extent. The yield of products derived from the excited singlet state steadily decreases with the linear energy transfer (LET), and in carbon and oxygen ion radiolysis its yield is less than 20% of that found in y-radiolysis. Product formation through radical mechanisms first slightly increases with particle LET until about 50 eV/nm, and then the total yields of all products decrease to half of that found in y-radiolysis. Much of the change in product yields with increasing LET can be explained by a radical mechanism, but it also appears that there is a change in initial radical formation due to a shift toward an increased probability of triplet excited-state formatiofi over that of singlet excited states.

Monte Carlo Simulation of Range and Energy Deposition by Electrons in Gaseous and Liquid Water

“…However, calculations have shown that the stopping power of electrons below ∼100 eV in solid hydrocarbons and in gases are substantially greater than that in liquid water. 47,48 Again there is also some discrepancy between the present results and those calculated by Kaplan and Sukhonosov. 44 Energy Loss Distribution.…”

“…These experiments are the only ones to use very low energy electrons, and they are often presented as representative of liquid water. However, calculations have shown that the stopping power of electrons below ∼100 eV in solid hydrocarbons and in gases are substantially greater than that in liquid water. , Again there is also some discrepancy between the present results and those calculated by Kaplan and Sukhonosov …”

Heavy Ion Radiolysis of Liquid Benzene

“…This trend can be observed for the iodobenzene formation for carbon ions at high iodine concentrations, see Figure . Similar results are observed for parent radical formation in cyclic alkanes. − It can also be observed for γ-rays, protons, and helium ions that at the highest iodine concentrations essentially all phenyl radicals have been scavenged, but the biphenyl yield is not zero. For all of the radiations used here, the biphenyl radical yield never decreases below a value of about 0.075 molecule/100 eV, as shown by the dotted line in Figure .…”

“…The lower yields for iodobenzene with carbon ions can be attributed to faster radical chemistry or lower initial radical yields. Decreasing radical yields with increasing LET were observed with cyclic alkanes. − Carbon ions of 10 MeV energy have a track average LET o of 686 eV/nm compared to the 0.2 eV/nm for γ-rays. Radical−radical reactions are enhanced in carbon ion tracks because of the increase in local radical concentrations .…”

“…Therefore, a thorough examination of its chemistry would give a significant amount of information on the radiolysis of liquid benzene. Iodine scavenging techniques have successfully examined primary radical formation in cyclic alkanes − and more recently in the γ-radiolysis of benzene . These techniques are expanded in this work to include different types of radiation in order to provide fundamental information on the fate of the phenyl radical in the radiolysis of liquid benzene.…”