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Seiichi Tagawa - One of the best experts on this subject based on the ideXlab platform.
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femtosecond pulse radiolysis study of geminate Ion recombinatIon in biphenyl dodecane solutIon
Radiation Physics and Chemistry, 2013Co-Authors: Takafumi Kondoh, Jinfeng Yang, Koichi Kan, Takahiro Kozawa, Seiichi Tagawa, K Norizawa, Atsushi Ogata, Yoichi YoshidaAbstract:The kinetics of geminate Ion recombinatIon was studied by the femtosecond pulse radiolysis of n-dodecane with biphenyl solutIon. The complicated biphenyl concentratIon-dependence behaviors of the transient absorptIons at 800 nm are observed and elucidated with a Monte Carlo simulatIon of geminate recombinatIon and charge transfer processes in the biphenyl-dodecane solutIon. The experimental data suggested the existence of n-dodecane excited radical catIon in the radiolysis. It plays very important roles especially in the high-concentratIon solutIon. The reactIon rate constant of the excited radical catIon with biphenyl molecule was 3.5 � 10 11 dm 3 mol � 1 s � 1 , which is comparable with the reactIon rate constant of the electron with biphenyl molecule. The contributIons of the geminate Ion recombinatIon, the charge transfer reactIon and the relaxatIon of the excited radical catIon were obtained as a functIon of the biphenyl concentratIon.
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subpicosecond pulse radiolysis in liquid methyl substituted benzene derivatives
Radiation Physics and Chemistry, 2007Co-Authors: Kazumasa Okamoto, Akinori Saeki, Takahiro Kozawa, Yoichi Yoshida, Seiichi TagawaAbstract:Abstract The early processes of radiatIon chemistry in the picosecond time regIon in methyl-substituted benzene derivatives have been investigated using subpicosecond pulse radiolysis. In o -xylene, a fairly slow geminate Ion recombinatIon was observed within 50 ps after the electron beam irradiatIon; this is due to the smaller electron mobility. The kinetic traces were analyzed using the Smoluchowski equatIon with exponential and modified-Gaussian (YGP) functIons as the distributIon of thermalized electrons. Only exponential functIons well reproduced the experimental data within 50 ps after the electron pulse.
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reactivity between biphenyl and precursor of solvated electrons in tetrahydrofuran measured by picosecond pulse radiolysis in near ultraviolet visible and infrared
Journal of Physical Chemistry A, 2007Co-Authors: Akinori Saeki, Takahiro Kozawa, Yuko Ohnishi, Seiichi TagawaAbstract:The initial decrease of solvated electrons in tetrahydrofuran (THF) upon additIon of biphenyl was investigated by picosecond pulse radiolysis. Transient absorptIon spectra derived from the biphenyl radical anIon (centered at 408 and 655 nm) and solvated electrons of THF (infrared) were successfully measured in the wavelength regIon from 400 to 900 nm by the extensIon of a femtosecond continuum probe light to near-ultraviolet using a second harmonic generatIon of Ti:sapphire laser and a CaF2 plate. From the analysis of kinetic traces at 1300 nm considering the overlap of primary solvated electrons and partial biphenyl radical anIon, C37, which is defined by the solute concentratIon to reduce the initial yield of solvated electrons to 1/e, was found to be 87 +/- 3 mM. The rate constant of solvated electrons with biphenyl was determined as 5.8 +/- 0.3 x 10(10) M(-1) s(-1). We demonstrate that the kinetic traces at both 408 nm mainly due to biphenyl radical anIon and 1300 nm mainly due to solvated electrons are reproduced with high accuracy and consistency by a simple kinetic analysis. Much higher concentratIons of biphenyl (up to 2 M) were examined, showing further increase of the initial yield of biphenyl radical anIon accompanying a fast decay component. This observatIon is discussed in terms of geminate Ion recombinatIon, scavenging, delayed geminate Ion recombinatIon, and direct IonizatIon of biphenyl at high concentratIon.
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subpicosecond pulse radiolysis study of geminate Ion recombinatIon in liquid benzene
Chemistry Letters, 2003Co-Authors: Kazumasa Okamoto, Akinori Saeki, Takahiro Kozawa, Yoichi Yoshida, Seiichi TagawaAbstract:Subpico- and picosecond pulse radiolyses were carried out to investigate geminate Ion recombinatIon in neat benzene. The fast decay of dimer radical catIon corresponding to geminate Ion recombinatIon with an electron was directly observed for the first time. The characteristic lifetime and average initial distance between a thermalized electron and its parent catIon were estimated to be 1.2 ps and 3.2 nm.
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Study on geminate Ion recombinatIon in liquid dodecane using pico- and subpicosecond pulse radiolysis
Radiation Physics and Chemistry, 2001Co-Authors: Akinori Saeki, Takahiro Kozawa, Yoichi Yoshida, Seiichi TagawaAbstract:Abstract Geminate Ion recombinatIon was studied by the laser-synchronized pulse radiolysis system which was developed at Osaka University. The time-dependent behavior of the catIon radicals in liquid n -dodecane on picosecond time scale showed a typical geminate decay. The experimental data were compared with the theoretical decay based on the diffusIon theory with the convolutIon technique in the time regIon within 1 ns.
Stephan Klock - One of the best experts on this subject based on the ideXlab platform.
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Ion recombinatIon correctIon for different IonizatIon chambers in high dose rate flattening filter free photon beams
Physics in Medicine and Biology, 2012Co-Authors: S Lang, J Hrbacek, Aidan Leong, Stephan KlockAbstract:Recently, there has been an increased interest in flattening-filter-free (FFF) linear accelerators. Removal of the filter results in available dose rates up to 24 Gy min(-1) (for nominal energy 10 MV in depth of maximum dose, a source-surface distance of 100 cm and a field size of 10×10 cm2). To guarantee accurate relative and reference dosimetry for the FFF beams, we investigated the charge collectIon efficiency of multiple air-vented and one liquid IonizatIon chamber for dose rates up to 31.9 Gy min(-1). For flattened beams, the Ion-collectIon efficiency of all air-vented IonizatIon chambers (except for the PinPoint chamber) was above 0.995. By removing the flattening filter, we found a reductIon in collectIon efficiency of approximately 0.5-0.9% for a 10 MV beam. For FFF beams, the Markus chamber showed the largest collectIon efficiency of 0.994. The observed collectIon efficiencies were dependent on dose per pulse, but independent of the pulse repetitIon frequency. Using the liquid IonizatIon chamber, the Ion-collectIon efficiency for flattened beams was above 0.990 for all dose rates. However, this chamber showed a low collectIon efficiency of 0.940 for the FFF 10 MV beam at a dose rate of 31.9 Gy min(-1). All investigated air-vented IonizatIon chambers can be reliably used for relative dosimetry of FFF beams. The order of correctIon for reference dosimetry is given in the manuscript. Due to their increased saturatIon in high dose rate FFF beams, liquid IonizatIon chambers appear to be unsuitable for dosimetry within these contexts.
Larry A Dewerd - One of the best experts on this subject based on the ideXlab platform.
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Ion recombinatIon and polarity correctIons for small volume IonizatIon chambers in high dose rate flattening filter free pulsed photon beams
Medical Physics, 2017Co-Authors: Megan A Hyun, Jessica R Miller, J Micka, Larry A DewerdAbstract:Purpose To investigate Ion recombinatIon and polarity effects in scanning and microIonizatIon chambers when used with digital electrometers and high-dose-rate linac beams such as flattening-filter-free (FFF) fields, and to compare results against conventIonal pulsed and continuous photon beams. Methods SaturatIon curves were obtained for one Farmer-type IonizatIon chamber and eight small-volume chamber models with volumes ranging from 0.01 to 0.13 cm3 using a Varian TrueBeam™ STx with FFF capability. Three beam modes (6 MV, 6 MV FFF, and 10 MV FFF) were investigated, with nominal dose-per-pulse values of 0.0278, 0.0648, and 0.111 cGy/pulse, respectively, at dmax. SaturatIon curves obtained using the Theratronics T1000 60Co unit at the UWADCL and a conventIonal linear accelerator (Varian Clinac iX) were used to establish baseline behavior. Jaffe plots were fitted to obtain PIon, accounting for exponential effects such as charge multiplicatIon. These values were compared with the two-voltage technique recommended in TG-51, and were plotted as a functIon of dose-per-pulse to assess the ability of small-volume chambers to meet reference-class criteria in FFF beams. Results Jaffe- and two-voltage-determined PIon values measured for high-dose-rate beams agreed within 0.1% for the Farmer-type chamber and 1% for scanning and microIonizatIon chambers, with the exceptIon of the CC01 which agreed within 2%. With respect to Ion recombinatIon and polarity effects, the Farmer-type chamber, scanning chambers and the Exradin A26 microchamber exhibited reference-class behavior in all beams investigated, with the exceptIon of the IBA CC04 scanning chamber, which had an initial recombinatIon correctIon that varied by 0.2% with polarity. All microchambers investigated, with the exceptIon of the A26, exhibited anomalous polarity and Ion recombinatIon behaviors that make them unsuitable for reference dosimetry in conventIonal and high-dose-rate photon beams. ConclusIons The results of this work demonstrate that recombinatIon and polarity behaviors seen in conventIonal pulsed and continuous photon beams trend accordingly in high-dose-rate FFF linac beams. Several models of small-volume IonizatIon chambers used with a digital electrometer have been shown to meet reference-class requirements with respect to Ion recombinatIon and polarity, even in the high-dose-rate environment. For such chambers, a two-voltage technique agreed well with more rigorous methods of determining PIon. However, the results emphasize the need for careful reference detector selectIon, and indicate that IonizatIon chambers ought to be extensively tested in each beam of interest prior to their use for reference dosimetry. This article is protected by copyright. All rights reserved.
Michael N R Ashfold - One of the best experts on this subject based on the ideXlab platform.
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studies of the plume accompanying pulsed ultraviolet laser ablatIon of zinc oxide
Journal of Applied Physics, 2002Co-Authors: Frederik Claeyssens, Andrew Cheesman, Simon J Henley, Michael N R AshfoldAbstract:The plume of ejected material accompanying pulsed laser ablatIon of a ZnO target at 193 nm in vacuum has been investigated using wavelength and spatially resolved optical emissIon spectroscopy and Langmuir probes. All lines in the observed optical emissIon spectra are assignable to electronically excited Zn+* catIons, and Zn* and O* neutrals, all of which emitting species we attribute to the result of electron–Ion recombinatIon processes in the gas phase following material ejectIon, laser–plume interactIons, IonizatIon, and thus, plasma formatIon. Various contributory components can be identified within the plume. Included among these are: a fast distributIon of Zn2+ Ions (observed via emissIon from highly excited states of Zn+*) together with an accompanying subset of fast electrons—the relative importance of which increases with increasing incident fluence on the target; a more abundant slower component involving both Zn+ and O+ Ions, which expand in associatIon with the main body of the electron distri...
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investigatIons of the plume accompanying pulsed ultraviolet laser ablatIon of graphite in vacuum
Journal of Applied Physics, 2001Co-Authors: Frederik Claeyssens, R J Lade, Keith N Rosser, Michael N R AshfoldAbstract:The plume accompanying 193 nm pulsed laser ablatIon of graphite in vacuum has been studied using wavelength, time and spatially resolved optical emissIon spectroscopy and by complementary Faraday cup measurements of the positively charged Ions. The temporal and spatial extent of the optical emissIons are taken as evidence that the emitting species result from electron–Ion recombinatIon processes, and subsequent radiative cascade from the high n,l Rydberg states that result. The distributIon of C neutral emissIon is symmetric about the surface normal, while the observed C+ emissIon appears localized in the solid angle between the laser propagatIon axis and the surface normal. However, Faraday cup measurements of the Ion yield and velocity distributIons, taken as a functIon of scattering angle and incident pulse energy, indicate that the total Ion flux distributIon is peaked along the surface normal. The derived Ion velocity distributIons are used as input for a two-dimensIonal model which explains the obse...
Akinori Saeki - One of the best experts on this subject based on the ideXlab platform.
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subpicosecond pulse radiolysis in liquid methyl substituted benzene derivatives
Radiation Physics and Chemistry, 2007Co-Authors: Kazumasa Okamoto, Akinori Saeki, Takahiro Kozawa, Yoichi Yoshida, Seiichi TagawaAbstract:Abstract The early processes of radiatIon chemistry in the picosecond time regIon in methyl-substituted benzene derivatives have been investigated using subpicosecond pulse radiolysis. In o -xylene, a fairly slow geminate Ion recombinatIon was observed within 50 ps after the electron beam irradiatIon; this is due to the smaller electron mobility. The kinetic traces were analyzed using the Smoluchowski equatIon with exponential and modified-Gaussian (YGP) functIons as the distributIon of thermalized electrons. Only exponential functIons well reproduced the experimental data within 50 ps after the electron pulse.
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reactivity between biphenyl and precursor of solvated electrons in tetrahydrofuran measured by picosecond pulse radiolysis in near ultraviolet visible and infrared
Journal of Physical Chemistry A, 2007Co-Authors: Akinori Saeki, Takahiro Kozawa, Yuko Ohnishi, Seiichi TagawaAbstract:The initial decrease of solvated electrons in tetrahydrofuran (THF) upon additIon of biphenyl was investigated by picosecond pulse radiolysis. Transient absorptIon spectra derived from the biphenyl radical anIon (centered at 408 and 655 nm) and solvated electrons of THF (infrared) were successfully measured in the wavelength regIon from 400 to 900 nm by the extensIon of a femtosecond continuum probe light to near-ultraviolet using a second harmonic generatIon of Ti:sapphire laser and a CaF2 plate. From the analysis of kinetic traces at 1300 nm considering the overlap of primary solvated electrons and partial biphenyl radical anIon, C37, which is defined by the solute concentratIon to reduce the initial yield of solvated electrons to 1/e, was found to be 87 +/- 3 mM. The rate constant of solvated electrons with biphenyl was determined as 5.8 +/- 0.3 x 10(10) M(-1) s(-1). We demonstrate that the kinetic traces at both 408 nm mainly due to biphenyl radical anIon and 1300 nm mainly due to solvated electrons are reproduced with high accuracy and consistency by a simple kinetic analysis. Much higher concentratIons of biphenyl (up to 2 M) were examined, showing further increase of the initial yield of biphenyl radical anIon accompanying a fast decay component. This observatIon is discussed in terms of geminate Ion recombinatIon, scavenging, delayed geminate Ion recombinatIon, and direct IonizatIon of biphenyl at high concentratIon.
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subpicosecond pulse radiolysis study of geminate Ion recombinatIon in liquid benzene
Chemistry Letters, 2003Co-Authors: Kazumasa Okamoto, Akinori Saeki, Takahiro Kozawa, Yoichi Yoshida, Seiichi TagawaAbstract:Subpico- and picosecond pulse radiolyses were carried out to investigate geminate Ion recombinatIon in neat benzene. The fast decay of dimer radical catIon corresponding to geminate Ion recombinatIon with an electron was directly observed for the first time. The characteristic lifetime and average initial distance between a thermalized electron and its parent catIon were estimated to be 1.2 ps and 3.2 nm.
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Study on geminate Ion recombinatIon in liquid dodecane using pico- and subpicosecond pulse radiolysis
Radiation Physics and Chemistry, 2001Co-Authors: Akinori Saeki, Takahiro Kozawa, Yoichi Yoshida, Seiichi TagawaAbstract:Abstract Geminate Ion recombinatIon was studied by the laser-synchronized pulse radiolysis system which was developed at Osaka University. The time-dependent behavior of the catIon radicals in liquid n -dodecane on picosecond time scale showed a typical geminate decay. The experimental data were compared with the theoretical decay based on the diffusIon theory with the convolutIon technique in the time regIon within 1 ns.
