Magnetic Field Effects on the Solute Luminescence of Alkane Solutions Irradiated with Heavy Ions

Abstract

The effects of track structure on the luminescence decays in cyclohexane and in 2,2,4-trimethylpentane (isoocatane) solutions of 2,5-diphenyloxazole (PPO) have been determined in the presence and in the absence of an external magnetic field. Irradiations were performed with protons of 1-15 MeV and with helium ions of 2-20 MeV energy. Companion studies were performed with {sup 90}Sr-{sup 90}Y {Beta}-radiolysis. The magnetic field effect is due to the hyperfine interaction of nuclear spins in the geminate pair of solvent radical ions produced. In both solvents, the effect of the magnetic field on luminescence decreases with increasing linear energy transfer (LET) from about 40% for {Beta}-particles to only a few percent with helium ions. Magnetic field effects with protons decrease in time whereas they are constant with {Beta}-particles. This result is attributed to the overlap of initially isolated spurs during the evolution of the proton track; the probability of nongeminate recombination increases with the number of neighboring ion pairs. The total luminescence intensity per incident particle remains constant with proton energy but increases slightly with increasing helium ion energy. At a given particle energy, the intensity is greater in cyclohexane than in isoocatane. The pulse shapes of the luminescence decays reflect themore » distributions in ion recombination times, and very little variation in luminescence decay rates is observed with increasing LET. 37 refs., 7 figs., 1 tab.« less