Ion beam pulse radiolysis

Very recently Kouchi et al. constructed an ion beam pulse radiolysis system and use it for the study of the LET effect in irradiated polystyrene thin films [106]. The nanosecond pulsed MeV ion beam with the variable repetition rate was obtained by chopping ion beams from a Van de Graaff. Time profiles of the excimer fluorescence from polystyrene thin films, excited by He+ impact, were... 

Basic Studies on Product Analysis and Ion Beam Pulse Radiolysis of Polymers. 102... 

The present chapter describes mainly the radiation effects of various ion beams on spin-coated polystyrene and PMMA films studied mainly by product analysis and by nanosecond ion beam pulse radiolysis. 

Direct measurement of short-lived reactive intermediates by time-resolved spectroscopic methods is very important for understanding the detailed mechanisms of radiation effects. Very recently a new ion beam pulse radiolysis system using optical multi-channel detection has been developed. Although the use of ion beam pulse radiolysis for studying the radiation effects of ion beams on polymers was first reported by us [3, 30], the new system is highly modified for investigating ion beam reactions. Electron beam pulse radiolysis was also carried out complementarily. 

The investigation of the ion beam interaction with polystyrene by means of ion beam pulse radiolysis has the advantage that the reactive intermediates can be directly detected. Time profiles of the excimer fluroescence from ion irradiated polystyrene were measured using the polystyrene thin films. Thus, the transient phenomenon excited by the ion with a definite kinetic energy was observed. 

In Fig. 5, the schematic diagram of the ion beam pulse radiolysis system with an optical emission spectroscope is also shown. The emission produced by the pulsed ion beam impact is detected through a monochromator by a fast photomultiplier tube (PMT) operated in a counting mode. The time profile of the emission is obtained by a coincident measurement between a photon and a... 

Fig. 5. The schematic diagram of the pulsing system and the ion beam pulse radiolysis system with an optical emission spectroscopy. PMT denotes photomultiplier tube HV, high voltage supply CFD, constant fraction discriminator TAC, time to amplitude converter and PH A, pulse height analyzer. From Ref. 36...

Fig. 10. Decay curves observed in electron beam, synchrotron radiation (SR), and ion beam pulse radiolysis of neat n-dodecane liquids...

Radiation effects of ion beams on PMMA films spin-coated on silicon wafers have been studied by ion beam pulse radiolysis. Figure 12 shows typical emission spectra of PMMA irradiated by 1 MeV nitrogen ion beams. The spectra changed drastically on irradiation. 

Very recently LET effects of ion beams on both standard polymers such as polystyrene and low molecular polyethylene model compounds (n-alkanes) have been studied by time-resolved spectroscopic methods, that is, ion beam pulse radiolysis techniques. Further basic studies are necessary so that the detailed mechanisms of ion beams on polymers can be clarified, especially LET effects and high density excitation effects. 

Katsumirra Y. (2001) Ion beam pulse radiolysis study on intra-track reactions in aqueous solutions. Res Chem Intermediates 27 AS) 333-341. 

The possible formation of an alloyed or a core-shell cluster depends on the kinetic competition between, on one hand, the irreversible release of the metal ions displaced by the excess ions of the more noble metal after electron transfer and, on the other hand, the radiation-induced reduction of both metal ions, which depends on the dose rate (Table 5). The pulse radiolysis study of a mixed system [66] (Fig. 7) suggested that a very fast and total reduction by the means of a powerful and sudden irradiation delivered for instance by an electron beam (EB) should prevent the intermetal electron transfer and produce alloyed clusters. Indeed, such a decisive effect of the dose rate has been demonstrated [102]. However, the competition imposed by the metal displacement is more or less serious, because, depending on the couple of metals, the process may not occur [53], or, on the contrary, may last only hours, minutes, or even seconds [102]. 

Electron-Transfer Reduction of 02. Within aqueous solutions the most direct means to the electron-transfer reduction of dioxygen is by pulse radiolysis. Irradiation of an aqueous solution by an electron beam yields (almost instantly 10-12 s) solvated electrons [e (aq)], hydrogen atoms (H-), and hydroxyl radicals (HO-)- If the solution contains a large excess of sodium formate [Na+ 0(0)CH] and is saturated with 02, then the radiolytic electron flux efficiently and cleanly reduces 02 to superoxide ion (O ) 21-25... 

Some new trends can be recognized in the points such as the interaction of short-lived active species in some spatial distributions measured by spin echo and pulse radiolysis methods. The application of polymers for drug-delivery systems is here discussed with reference to low temperature radiation polymerization techniques. Ion beam irradiation of polymers is also reviewed for which further research is becoming important and attractive for so-called LET effects and high density excitation problems. In the applied fields the durable polymers used in strong and dense irradiation environments at extremely low temperature are here surveyed in connection with their use in nuclear fusion facilities. 

The pulse radiolysis method is a powerful means of studying the kinetics in radiation chemistry. We investigated the ion beam interaction with polystyrene using this method. It is a unique system, because pulse radiolysis is usually an electron pulse radiolysis. 

Very recently. LET effects on fluorescence lifetimes of low molecular polyethylene model compounds (n-alkane) have been studied by many kinds of pulse radiolysis - methods such as electron beam, ion beam and synchrotron radiation (SR) [40] pulse radiolysis techniques [41]. Figure 10 shows time profiles of the fluorescence from neat n-dodecane liquids irradiated many kinds of radiation with different LET. The fluorescence lifetimes from irradiated neat... 

The hydrated electron is commonly detected by pulse radiolysis with electron beams. In the case of highly-structured track, this very reducing species reacts easily with oxidant like OH radical in its vicinity at earliest time after the ionization track is formed. That is the reason why it is a real challenge to detect this species yet with heavy ion irradiation. Giving a G-value remains delicate because the concentrations are lower than 10 M and dose must be measured with a high accuracy. As it is shown in Fig. 5, the time dependence of hydrated electron is typical of a track structure in space and time in the first 100 ns the concentration of initial hydrated electron is at least divided... 

Fig. 8. Superoxide radical G-values as a function of LET. The square symbol is the common yield accepted with y-rays and high energy electton beam irradiation. Plain lines are from scavenging experiments with C, Ne and Ni ion beam by Laverne and Schuler [Cited in Refs. 41 and 42]. The circle and triangle symbols are from track-segment pulse radiolysis experiments. Dash line is from Monte Carlo simulation.

In the near future, the ion-beam radiation-chemist community will probably understand earlier processes in the track of heavy ions. This supposes two things accelerators must deliver shorter pulses than those used currently and the detection must be more sensitive and highly time-resolved. That means a picosecond pulse radiolysis research with heavy ions. That is not a foolish project because new designs of accelerators for proton and heavier ions have already started. Physics of plasma has made recent progress and probably in the next year will appear the first results in radiation chemistry with protons with at least a picosecond time resolution. A few intentions have already been published. ... 

Chitose N, Katsmnura Y, Domae M, Zuo Z, Murakami T. (1999) Radiolysis of aqueous solutions with pulsed helium ion beams — 2. Yield of S04" formed by scavenging hydrated electron as a function of S2082-concentration. Rjid Phys Chem 54(4) 385-391. 

Chitose N, Katsumura Y, Domae M, Cai ZL, Muroya Y, Murakami T, LaVerne JA. (2001) Radiolysis of aqueous solutions with pulsed ion beams. 4. Product... 

Two distinct XeBr formation processes in electron-beam-excited Xe-Br2 mixtures have been identified in nanosecond pulse radiolysis experiments. One formation process, involving ion recombination, could be slowed relative to the second process, involving excitation energy transfer from Xe to Brz, by using very low electron-beam intensities, thereby allowing a kinetic analysis of the second process to be made. XeBr (B) emission at 280 nm has been observed following 193 nm excitation of IBr in Xe-IBr mixtures. ... 

Combination of pulse radiolysis and two-laser flash photolysis will be another interesting subject of three-beam excitation chemistry to be investigated in the near future. In this case, radical ions generated during pulse radiolysis will be excited by the successive two lasers. That is, one can introduce additional pathways to the reaction scheme indicated in Scheme 2.3. Utilization of a dyad or triad molecular system will realize fast intramolecular reaction systems applicable to the multibit molecular memory. 

Product analysis Time resolved measurements such as pulse radiolysis system were described in the previous section. For product analysis, most of ordinary analyzing procedures in traditional radiation chemistry can be applied, such as changes in molecular weight, gel fraction, infrared or ultra-violet spectroscopy. In the case of ion beam, elaboration to characterize surface or very thin layers has been tried. For example, development of spin coated thin film is used for monitoring gel fraction [42]. Another characteristic may be depth dependent phenomena. Depth-profile of optical absorption is performed as... 

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