Fluorescence in the Heavy Ion Radiolysis of Benzene

Abstract

Fluorescence emission has been measured in the radiolysis of neat liquid benzene with 1-15 MeV protons, 5-20 MeV helium ions, 5-30 MeV lithium ions, and 10-30 MeV carbon ions using single photon counting techniques. Companion studies were performed with 90 Sr-90 Y -particles with an average energy of about 1.66 MeV. Within 30-50 ns following the passage of the heavy particles the fluorescence intensity decreases rapidly and then levels off to a much slower decay rate which is very nearly the same for -particles and high-energy protons and helium ions. The lifetimes of both the fast and slow components of the fluorescence decrease with increasing linear energy transfer (LET), and the magnitude of the fast component increases with respect to the slower one. Quenching of the fluorescence by radicals or other transient species produced in the particle track are thought to be responsible for the observations. At low LET the relative yield of the fluorescence decreases with increasing LET, presumably due to the quenching. However, at higher LET the fluorescence yield increases with increasing LET. Self-annihilation reactions of the triplet states to give singlet states may be the source of these observations. These experiments are the first in which the temporal variation of fluorescence emission has been determined in a neat hydrocarbon liquid irradiated with heavy ions.

Molecular Hydrogen Production in the Radiolysis of High-Density Polyethylene

“…A decrease in the yield of excited states with increasing LET has been determined in the radiolysis of benzene. 33 The present results with protons and helium ions using pellets are significantly higher than found in most previous reports as shown in Figure 4. [16][17][18] In these studies polyethylene samples were irradiated in high vacuum by low-energy (0.1-1.5 MeV) particles.…”

“…If one or both states are quenched, the result will be fewer excited states to react with molecular hydrogen, resulting in an increase in its yield as is observed. A decrease in the yield of excited states with increasing LET has been determined in the radiolysis of benzene …”

Radical yields in the radiolysis of cyclic compounds

“…Iodine can scavenge atomic precursors to H 2 , but it has virtually no effect on the fate of the singlet excited states. There is a strong correlation of H 2 yields with the singlet excited state decomposition in benzene (LaVerne, 1996) and the data presented here suggest that a similar process probably occurs in pyridine.…”

Excited Singlet-State Yields in Hydrocarbon Liquids Exposed to X-rays

“…Consequently quenching of excited states by radicals will also be less. LaVerne reports that the lifetime of the benzene singlet is less for heavy-particle radiation at high LET . The LET of the heavy particles was between 10 and 1000 eV/nm.…”