Y. Katsumura

Picosecond pulse radiolysis studies on geminate ion recombination in saturated hydrocarbon

Abstract The geminate recombination kinetics of the excess electron and the electron hole are discussed, based on time-resolved data on picosecond and nanosecond time scales. The recombination times of the excess electron and the electron hole are evaluated to be 3 ps for cyclohexane on the basis of the comparison between the experimental and the calculated results. The spin correlation decay of the geminate ion pairs and the triplet state formation before the spin correlation loss have also been discussed. The rapidly decaying species with very broad absorption spectra, which are similar to the absorption spectra of the cation radicals of saturated hydrocarbons, have been observed in neat saturated hydrocarbons in the sub-nanosecond and a few nanosecond time regions. The identification of the rapidly decaying species were not definitely made but those species are tentatively assigned to the excited states and/or the tail of the geminate cation radicals of saturated hydrocarbons.

Picosecond pulse radiolysis studies on the formation of excited singlet states of solute molecules in several saturated hydrocarbon and ethanol solvents

Abstract Two kinds of the formation components of excited singlet states of solute molecules have been observed in the picosecond time region in methylcyclohexane, 3-methylpentane, and iso -octane as well as in cyclohexane, as reported previously. The ratios of two components are significantly dependent on solute concentrations and kinds of solvents. A fairly large amount of the slower formation component has been observed in cyclohexane and methylcyclohexane, little in iso -octane, and none in ethanol. The slower component is mainly due to the solute geminate ion recombination and partly due to the energy transfer from the excited singlet states of solvent molecules. The faster component has not been made clear, but could be due to Cerenkov light. The life-time of the excited singlet state of cyclohexane was directly measured to be 1.1 ± 0.1 ns.

Study on the excited state of liquid alkanes and energy transfer process by means of picosecond pulse radiolysis

Abstract Fluorescence from saturated hydrocarbon in liquid phase irradiated by high energy electron beam has been measured by the picosecond pulse radiolysis technique. With the aid of convolution technique, precise lifetimes of fluorescent excited state of n-alkanes were determined. The lifetime increases with increasing the number of carbon atoms from 0.7 (±0.1) ns for n-hexane to 4.3(±0.2) ns for n-pentadecane. In the presence of solute such as CCl4 or benzene in cis-decalin, energy transfer from excited cis-decalin to solute molecules occurs. Based on diffusion kinetics including transient term, effective reaction radii were determined to be ≈14 A and ≈7 A for cis-decalin-CCl4 and cis-decalin-benzene systems, respectively. Energy transfer process in the liquid saturated hydrocarbon is discussed in terms of the lifetime of the excited state, the effective reaction radius and the transient term of diffusion kinetics.

Radiolysis of high temperature water

Abstract The yields of the primary products for water radiolysis were estimated in the temperature range of 25 to 250°C from the product analyses of three kinds of aqueous systems irradiated with γ-rays and farst neutrons. Model calculations were carried out using these primary yields to simulate the water radiolysis reactions in nuclear reactor.

Evidence for two fast formation processes of solute excited states in liquid toluene solutions studied by picosecond single pulse radiolysis

A technique for the production and observation of excited states with about 10 picosecond (ps) time resolution using the picosecond single electron pulse from an S-band linear accelerator is reported. Two fast formation processes of excited singlet states of solute molecules in liquid toluene have been directly observed in the picosecond time range. The faster process is an ultra fast one that is completed immediately after the picosecond electron pulse. This is hardly quenched by CCl4 or TEA, and does not become slower even in the solid state. However, CCl4 and TEA remove the faster formation process to a great extent, if there exists a very high concentration of CCl4 and TEA. Geminate pairs are believed to play an important role in the faster formation process of solute excited states in toluene.

Fast neutron irradiation effects. III: Sensitivity of alanine systems for fast neutron having an energy of ∼ 1 MeV

Abstract Relative G -values of alanine dosimeters for fast neutron with an energy of 1 MeV are determined to be 0.4 as compared with 60 Co γ-ray irradiation. The values are almost independent of paraffin content. The neutron irradiation process in alanine dosimeter is discussed

Fast neutron irradiation effects—I. Dosimetry

Abstract A dosimetry of mixed field, neutron and γ-ray, has been carried out by the activation method in a fast neutron source reactor “YAYOI,” which has been used for the study of fast neutron irradiation effects on organic materials and microorganisms. Neutron flux and energy distribution were obtained by an unfolding calculation based on the activation analysis. Absorbed dose was determined as a function of the distance from the center of the reactor core in a hole called “Glory Hole” used for irradiation of various materials. Contribution of absorbed dose from γ-rays coexisting with neutron was evaluated by measuring peroxide radicals formed in irradiated polytetrafluoroethylene, PTFE, which is insensitive to the neutron component. After evaluating the radiation field, relative sensitivities of popular dosimeters such as red acrylate, radiachromic, and alanine dosimeter for last neutron irradiation were determined by comparison with 60Co γ-ray irradiation. Characteristics of the mixed field dosimetry and LET effect of recoil protons in samples at different neutron fields are discussed.

Pulse radiolysis studies on short-lived intermediates in radiation-induced polymerization of bulk styrene and methanol-styrene solutions

Abstract Primary processes of radiation-induced polymerization of bulk styrene at room temperature and effects of methanol have been studied by means of pulse radiolysis. Cationic intermediates such as the bonded dimer cation radical, which is the initiating species of radiation and photo-induced cationic polymerization, have been directly observed for the first time in bulk styrene. The rate constant of the reaction of the bonded dimer cation radical with a styrene monomer (trimerization and the first step of the cationic polymerization) has been directly determined to be the order of 106M−1sec−1. Methanol reacts with cationic and anionic species and enhances the absorption of radical species at 310 nm.

STUDY ON THE BEHAVIOR OF RADIOLYTICALLY PRODUCED HYDROGEN IN A HIGH-LEVEL LIQUID WASTE TANK OF A REPROCESSING PLANT: HYDROGEN CONSUMPTION REACTION CATALYZED BY Pd IONS IN THE SIMULATED SOLUTION

Abstract It is well known that not all of the hydrogen formed in high-level liquid waste comes out in the gas phase because hydrogen is consumed by some unclarified secondary reaction. Using a simulated waste solution, it was found that the H2 consumption reaction is not caused by radiation as was thought but is caused by a catalytic effect of Pd ions, which suggests that the same reaction proceeds in actual solution. Using the catalytic reaction rate constant measured in the simulated solution, the analysis showed that the H2 concentration in the gas phase does not reach its explosion limit of 4% even if the sweeping air stops for a long time.

Current status of the ultra-fast pulse radiolysis system at NERL, the University of Tokyo

In order to investigate the early events in radiation physics and chemistry, a new pulse radiolysis system with higher time resolution based on the pump-and-probe method has been developed at Nuclear Engineering Research Laboratory (NERL), The University of Tokyo. Electron pulses with duration of a few picoseconds are generated from an 18 MeV S-band linear accelerator (linac) by using a combination of a laser photocathode rf-gun and a chicane-type magnetic compressor. The pulses are synchronized with a femtosecond laser pulse as the analyzing light. The precision of synchronization between the pump and the probe has attained within 1.6 ps (rms). By converting the fundamental laser into white light continuum, it allows to measure in the wavelength range from 400 to 1100 nm. With a sample cell having an optical path of 1 mm, a time resolution of 5 ps has been achieved.