Picosecond Pulse Radiolysis System Research Articles

Construction of nanosecond and picosecond pulse radiolysis system with supercontinuum probe

Supercontinuum (SC) with photonic crystal fiber (PCF) is a new technique of pulsed white light generation. The pump beam and the white probe light are necessary for pump–probe pulse radiolysis. The improvement of pulse radiolysis system can be expected by using PCF based SC as probe light. The source size of white light that depends on core size of PCF will be improved. Nanosecond time resolution pulse radiolysis with SC probe was successfully conducted about pure water sample. The absorption decay and spectrum of hydrated electron was obtained. As SC is a short pulse, it would be applicable for picosecond time resolution pulse radiolysis based on the stroboscopic method.

Improvements in time resolution and signal-to-noise ratio in a compact pico-second pulse radiolysis system

A compact pico-second pulse radiolysis system has been developing at Waseda University for studying primary processes in radiation chemistry. The system is composed of a photo-injector system and a pico-second all-solid-state laser system. An infrared (IR) and an ultraviolet (UV) laser pulses are obtained from mode-locked Nd:YLF laser system and used for generation of the white light continuum as a probe light and the irradiation to the Cu cathode of a photo-cathode RF-gun, respectively. To improve signal-to-noise (S/N) ratio and time resolution of this pulse radiolysis system, we optimized both probe light and pump electron beam. As a result, our pico-second pulse radiolysis system has been enough to study the primary processes of radiation chemistry. The experimental results and the improvements of our system are described in this paper.

Development of compact picosecond pulse radiolysis system

A pulse radiolysis technique is known as a powerful method to study the primary processes in radiation chemistry. However, a large-sized accelerator and a huge cost should be required for the construction and operation of pulse radiolysis system. Very recently, the new compact picosecond pulse radiolysis system composed of the small size accelerator and laser system has been developed at RISE, Waseda University. To evaluate the performance of the system, the absorption measurement of hydrated electrons was carried out as a preliminary experiment. As a result, the time resolution was estimated to be approximately 26ps. It is analytically calculated to be approximately 30ps (FWHM) with the convolution among the beam size, the bunch length of electron beam, the laser spot size, and the laser pulse length. The experimental value is in good agreement with the calculated one. The system has been developed to get better S/N ratio and will be applied for the study of primary processes in radiation chemistry of polymer system.

Development of laser-synchronized picosecond pulse radiolysis system

A new picosecond pulse radiolysis system for absorption spectroscopy by using a 20 ps single electron pulse from the 28 MeV L-band electron linac and a single femtosecond laser pulse was developed for the research of the ultra-fast phenomena in primary processes of radiation chemistry. The electron pulse was used for the irradiation source and the laser pulse was used for the analyzing light. Both pulses are synchronized within several picoseconds by controlling a common radio frequency. The available analyzing light was from 360 to 1000 nm by using white-light continuum.

Studies of geminate ion recombination and formation of excited states in liquid n-dodecane by means of a new picosecond pulse radiolysis system

A new ps pulse radiolysis system for optical absorption spectroscopy from visible to infrared regions was developed to investigate the primary processes of radiation chemistry. 10 ps electron pulses from a 28 MeV electron linac and ps diode lasers were used as irradiation source and analyzing light, respectively. The ps diode lasers were synchronized with the electron pulses. The time profile of the absorption was obtained by changing the time difference between the electron and the laser pulses. The time resolutions of the system were a few tens ps. The time-dependent behavior of the cation radicals, electrons and excited states in primary processes in liquid n-dodecane was studied by using the new system. The decays of the cation radicals and electrons showed the geminate ion recombination based on the diffusion theory in the time region within 2 ns.

Picosecond pulse radiolysis system at nuclear engineering research laboratory, University of Tokyo

About 10 years have passed since construction of an S-band linac with a capability of acceleration of single bunched beams (picosecond single beams). Several kinds of picosecond pulse radiolysis systems both for emission spectroscopy and for absorption spectroscopy using this ultra short electron pulse have been developed. All of these pulse radiolysis systems are categorized according to detection techniques such as direct detection (fast detection) and sampling like detection.

Some recent radiolysis works by means of a new picosecond pulse radiolysis system “Twin LINAC System”

A new picosecond pulse radiolysis “Twin LINAC System” has been constructed recently at Nuclear Engineering Research Laboratory at the University of Tokyo. The time resolution of the system is 20 ps and the system has a versatile capability for pulse radiolysis study. The outline of the facility is introduced. Some research carried out using the facility is presented. The examples are radiolysis of CCl4 and n-C21H44.

Yields of Solvated Electrons at 30 Picoseconds in Water and Alcohols

Abstract Direct measurements of the yield of hydrated electrons in aqueous solutions and solvated electrons in alcohols were carried out using a stroboscopic picosecond pulse radiolysis system. The yield of solvated electrons was obtained by simultaneous consideration of the pulse shape and radiation doses. The yield at 30 ps after irradiation, G(eaq−)30ps, was determined to be 4.8±0.3 products per 100 eV as compared to the G(eaq−)100ns of 2.7. Experimental values, including the present ones, are higher by 0.3 than the theoretical ones calculated using the spur diffusion model in the time period from 3×10−11 to 10−8 s. Nevertheless, both results show a quite similar time dependence, i.e., fast decay of hydrated electrons in spur reactions. The G-values of solvated electrons at 30 ps were also determined in alcohols. The G-value of solvated electron is 3.4±0.3 in both methanol and ethanol, 2.0±0.3 in 1-propanol and 2.3±0.3 in ethylene glycol.

THE YIELD OF HYDRATED ELECTRONS AT 30 PICOSECONDS

Abstract Direct measurements of the yield of hydrated electrons in aqueous solutions were carried out using a stroboscopic picosecond pulse radiolysis system. The yield 30 ps after irradiation, G(eaq−)30ps, was determined to be 4.8±0.3 products per 100 eV as compared to the G(eaq−)100ns of 2.7.

The formation of solute excited triplet states via geminate ion recombination in cyclohexane solutions of biphenyl and pyrene on subnanosecond and nanosecond timescales

The formation of the solute excited triplet states via geminate ion recombination observed for both biphenyl and pyrene solutions in cyclohexane has been studied by using a picosecond pulse radiolysis system for absorption spectroscopy with the time resolution of 8o ps. The ratio of the formation rate of the solute excited triplet state of the decay rate of the solute anion changes in a time range between 5 and 20 ns. It is very well correlated with the spin correlation decay of geminate ion pairs, which are initially paired with each other in a singlet state. The formation of the solute triplet state was observed even on a timescale shorter than 5 ns, although loss of spin correlation is negligibly small.

Picosecond pulse radiolysis and laser flash photolysis studies on polymer degradation of polystyrene and poly-α-methylstyrene

Recently early events in photolysis of polystyrene (PSt) solutions in chloroform and in 1,4-dioxane have been made clear by using a nanosecond laser flash photolysis system (Nd-YAG: 265 nm) at Hahn-Meitner-Institut [1]. Early events in radiolysis of PSt solution have also been studied by using a picosecond pulse radiolysis system at Univ. of Tokyo [2]. In the present paper, the difference and the similarity between photolysis and radiolysis of PSt and poly-α-methylstyrene (P-α-MeSt) are discussed. Important results are as follows; 1. (1) In both cases of radiolysis and photolysis, strong absorptions of intramolecular excimer have been observed for PSt ( λmax = 530 nm) and P-α-MeSt ( λmax = 520 nm) solutions in dioxane and cyclohexane, in addition to the monomer and excimer fluorescence of these polymers. In these solutions, those polymers are hardly decomposed. 2. (2) In both radiolysis and photolysis, charge-transfer complexes (PSt +δ, Cl −δ or P-α-MeSt +δ, Cl −δ) have been observed for PSt and P-α-MeSt solutions in chloroform (CHCl 3) and in carbon tetrachloride (CCl 4). In these solutions, polymers are effectively decomposed. The charge-transfer complexes are precursors of macroradicals. 3. (3) The charge-transfer complexes are mainly produced from ion pairs (PST +…Cl − or P-α-MeSt +…Cl −) in the case of radiolysis and from exciplexes of excited polymer molecules with solvent molecules in the case of photolysis. 4. (4) Since the presence of oxygen is prerequisite to main chain cleavage of PSt in CHCl 3 and in CCl 4, it is important to note that oxygen is not involved in initial stages of the main process of macroradical formation.

Performance and improvements of an electron accelerator producing a picosecond single electron pulse

A 35 MeV S-band linac with a subharmonic prebunching cavity operated at 476 MHz, 1/6 of the main accelerating microwave frequency of 2856 MHz, is available to compose a picosecond pulse radiolysis system with a response down to 18 ps, which has provided a very strong means of studying early events in radiation chemistry, fast response scintillators and radiation damage of ionic crystals since 1977. Recently the improvement of the fluctuation of the intensity and the time jitter between the electron pulse and a pre-trigger for the detection system has been carried out. The time jitter between beam pulse and a pre-trigger for measurement is ±6 ps. The total time jitter of the pulse radiolysis system, including the linac and a streak camera, is ±11 ps.

Fast Electron Reactions in Concentrated Solutions of Amino Acids and Nucleotides

ALDRICH, J. E., LAM, K. Y., SHRAGGE, P. C., AND HUNT, J. W. Fast Electron Reactions in Concentrated Solutions of Amino Acids and Nucleotides. Radiat. Res. 63, 42-52 (1975). A picosecond pulse radiolysis system has been used to study the electron attachment processes encountered in concentrated solutions (0.1-3 M). These highly concentrated solutions approximate the conditions of a biological cell. The reaction eaq- + scavenging molecule has been observed for a range of biologically important molecules. The rate constants depend upon the concentration of the solute molecules and the pH of the solution. As well, the initial yield of eq- at 30 psec is reduced markedly in concentrated solutions of scavengers such as amino acids and mononucleotides; the initial process is too fast to be explained by normal chemical kinetics. The scavenger which is unique is the hydrogen ion, Haq+, which causes no observable reduction of the enq- yields, but has a normal rate constant of reaction with eaq-. With other electron scavengers, a general relationship between the efficiency of reducing the initial yield of eaq- and the rate constant, k(,,aq-+s) in concentrated solutions is obtained. This relationship indicates that both the eaq- and its precursor react with the same efficiency toward the solute molecules.

Picosecond Pulse Radiolysis Studies. I. The Solvated Electron in Aqueous and Alcohol Solutions

Observations of the solvated electron in water and the common aliphatic alcohols have been made in the time region ∼ 20–350 psec. Molar concentrations of acid have been used to scavenge eaq− and k(eaq−+Haq+) has been measured as (1.2 ± 0.2) × 1010 liter/mole·sec for [Haq+] from 0.5 to 5.0M. The factors limiting the time response of our picosecond pulse radiolysis system are discussed. The time of formation of esol− is estimated to be less than 10 psec for all solvents studied. The yield of solvated electrons in alcohols has been measured to be approximately one-third of the yield in water at picosecond times.