Ionic reactions occurring in the irradiation of carbon dioxide – oxygen mixtures at very high dose rates

Ozone yields have been measured in CO2–O2 mixtures irradiated with single pulses from a Febetron 705 at a dose rate of 1026 eV g−1 s−1. Low concentrations of carbon dioxide in oxygen rapidly reduce the yield from G(O3) = 12.8 to G(O3) ≈ 9. At 300 Torr total pressure, as the oxygen concentration is reduced, the ozone yield decreases from this yield of G(O3) ≈ 9 to an extrapolated yield, at zero oxygen, of close to G(O3) = 7.8. Changes of yields with composition are explained in terms of ionic reactions, the main neutralization process being[Formula: see text]At 700–1500 Torr total pressure, the ozone yields are lower than that at 300 Torr. It is proposed that clustering of the ionic species affects the products of the neutralization reaction.Sulfur hexafluoride suppresses the dissociative neutralization reaction and ozone yields from mixtures containing 1.5–2% SF6 are those predicted from direct neutral dissociation processes in the pure gases.Computer calculations are used to compare the experimental results to the proposed mechanism and, in general, a good fit is obtained.

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The radiation chemistry of carbon monoxide at very high dose rates

Canadian Journal of Chemistry ◽

10.1139/v70-511 ◽

1970 ◽

Vol 48 (19) ◽

pp. 3029-3033 ◽

Cited By ~ 3

Author(s):

C. Willis ◽

O. A. Miller

Keyword(s):

Carbon Dioxide ◽

Carbon Monoxide ◽

Excited State ◽

Oxygen Atom ◽

Dose Rate ◽

Electron Accelerator ◽

Radiation Chemistry ◽

High Dose ◽

Dose Rates ◽

Very High

Carbon monoxide has been irradiated with single intense pulses from an electron accelerator at a dose rate of ~ 2 × 1027 eV g−1 s−1. The yield of carbon dioxide obtained was G(CO2) = 0.7 ± 0.1 with a very small yield of carbon suboxide, G(C3O2) ≤ 0.02.Addition of propene reduces the carbon dioxide yield to almost zero while addition of propane has no effect. This suggests that propene is acting as an oxygen atom scavenger rather than as a quencher of an excited state of carbon monoxide. However, rate constant data do not support this suggestion and it is concluded that the residual yield of carbon dioxide observed at high dose rates arises from reaction 9[Formula: see text]where CO+ is in an A2Π or B2Σ+ state.

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High Dose Rate Oxygen Implantation for Formation of Silicon-on-Insulator Structures

MRS Proceedings ◽

10.1557/proc-201-259 ◽

1990 ◽

Vol 201 ◽

Author(s):

E. Cortesi ◽

F. Namavar ◽

R. F. Pinizzotto ◽

H. Yang

Keyword(s):

Dose Rate ◽

Silicon Surface ◽

High Dose Rate ◽

Silicon On Insulator ◽

High Dose ◽

Surface Oxide Layer ◽

Dose Rates ◽

Pit Formation ◽

Lower Dose Rate ◽

Very High

AbstractWe have studied Separation by IMplantation of OXygen (SIMOX) processes using very high dose rates (40–60 μA/cm2). For a dose of 4 × 1017 O+/cm2 at 160 keV, the structure formed by implantation at 50 μA/cm2 is very similar to that associated with lower dose rates. The same dose implanted at a dose rate of 60 μA/cm2, however, results in the formation of pits in the silicon surface as well as a somewhat different oxide structure. Implantation through a surface oxide layer appears to result in a structure similar to that associated with lower dose rate implantation. These and higher dose samples suggest that the threshold for pit formation is related to both dose rate and dose.

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Isotope effects in the gas phase radiolysis of H2S and D2S

Canadian Journal of Chemistry ◽

10.1139/v76-391 ◽

1976 ◽

Vol 54 (17) ◽

pp. 2767-2772

Author(s):

Robert D. McAlpine ◽

O. A. Miller ◽

A. W. Boyd

Keyword(s):

Dose Rate ◽

Gas Phase ◽

Isotope Effects ◽

High Dose ◽

Dose Rates ◽

Kinetic Isotope ◽

A Value ◽

Straight Line ◽

Separation Factors ◽

Very High

Gas phase radiolysis studies have been carried out on mixtures of H2S and D2S using as irradiation sources, either a Gammacell or a Febetron 705 pulsed electron accelerator. Separation factors (α = (H/D)prod ÷ (H/D)react) were obtained for various values of xD (the mole fraction of D2S), dose rate and temperature, as well as with the addition of SF6. All of the observed α values, for 0.2 ≤ xD ≤ 0.8, fall on the following empirical straight line.[Formula: see text]The addition of neon to a D2S/H2S mixture gives a value of α which decreases as the partial pressure of neon increases. For a 70% D2S/30% H2S mixture, &([a-z]+); = 1.9 ± 0.1 for the pure mixture and 1.28 ± 0.08 when 90 kPa of neon has been added to 10 kPa of the mixture. The &([a-z]+); values described by eq. 1 are interpreted as arising from kinetic isotope effects in the reactions of (translationally) hot H or D atoms with H2S, HDS, or D2S to form H2, HD or D2.Hydrogen yields from the gas phase radiolysis of pure H2S and pure D2S have been determined for dose rates from 4 × 1016 to 2 × 1028 eV g−1 s−1. Using dose rates of up to 2 × 1027 eV g−1 s−1, ΔG = G(H2) − G(D2) = 0.5. For the highest dose rate used (2 × 1028 eV g−1 s−1), ΔG = 1.5. The larger value of ΔG at very high dose rates is thought to arise from the dissociative neutralization processes. A possible mechanism is discussed.

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Carbon monoxide yields in the radiolysis of carbon dioxide at very high dose rates

Canadian Journal of Chemistry ◽

10.1139/v70-323 ◽

1970 ◽

Vol 48 (13) ◽

pp. 1951-1954 ◽

Cited By ~ 11

Author(s):

C. Willis ◽

A. W. Boyd ◽

P. E. Bindner

Keyword(s):

Carbon Dioxide ◽

Carbon Monoxide ◽

Dose Rate ◽

Low Dose ◽

High Dose ◽

Dose Rates ◽

Low Dose Rate ◽

Electron Scavenger ◽

The Difference ◽

Carbon Monoxide Yield

Carbon dioxide has been irradiated with electron pulses at a dose rate of 2 × 1027 eV g−1 s−1. The measured carbon monoxide yield is G(CO) = 7.8 ± 0.3. Addition of SF6, an electron scavenger, reduces this yield to G(CO) = 4.8 which is the same, within the experimental error, as the low dose rate yield G(CO) = 4.5 ± 0.5. The effect of SF6 and the difference between the high and low dose rate yields is explained by suppression of dissociative neutralization of the C2O4+ ion.

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Radiolysis of cyclohexane with perfluorocyclohexane at very high dose rates

Canadian Journal of Chemistry ◽

10.1139/v70-079 ◽

1970 ◽

Vol 48 (3) ◽

pp. 501-503 ◽

Cited By ~ 3

Author(s):

N. H. Sagert

Keyword(s):

Proton Transfer ◽

Radical Reactions ◽

High Dose ◽

Geminate Recombination ◽

Dose Rates ◽

Conventional Dose ◽

Electron Scavenger ◽

Neutralization Process ◽

High Concentrations ◽

Very High

The radiolysis of liquid cyclohexane using perfluorocyclohexane as an electron scavenger has been examined at very high dose rates. The dose rates, 1027 to 1028 eV/g s, were such that geminate recombination of ions is essentially unaffected by dose rate, but high concentrations of radicals are produced, leading to radical–radical reactions. Up to 0.7 G units of the mixed dimer, C6F11•C6H11, were produced indicating that large concentrations of C6F11 radicals are formed in the neutralization process. Thus, at conventional dose rates (1016 eV/g s), C6F11H is probably produced by reactions of C6F11 radicals rather than by proton transfer to a perfluorocyclohexane or perfluorocyclohexyl anion.

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Back to the Future: Very High-Energy Electrons (VHEEs) and Their Potential Application in Radiation Therapy

Cancers ◽

10.3390/cancers13194942 ◽

2021 ◽

Vol 13 (19) ◽

pp. 4942

Author(s):

Maria Grazia Ronga ◽

Marco Cavallone ◽

Annalisa Patriarca ◽

Amelia Maia Leite ◽

Pierre Loap ◽

...

Keyword(s):

Radiation Therapy ◽

Current Knowledge ◽

High Energy ◽

High Dose Rate ◽

Point Of View ◽

High Dose ◽

Dose Rates ◽

High Energy Electrons ◽

Very High Energy ◽

Very High

The development of innovative approaches that would reduce the sensitivity of healthy tissues to irradiation while maintaining the efficacy of the treatment on the tumor is of crucial importance for the progress of the efficacy of radiotherapy. Recent methodological developments and innovations, such as scanned beams, ultra-high dose rates, and very high-energy electrons, which may be simultaneously available on new accelerators, would allow for possible radiobiological advantages of very short pulses of ultra-high dose rate (FLASH) therapy for radiation therapy to be considered. In particular, very high-energy electron (VHEE) radiotherapy, in the energy range of 100 to 250 MeV, first proposed in the 2000s, would be particularly interesting both from a ballistic and biological point of view for the establishment of this new type of irradiation technique. In this review, we examine and summarize the current knowledge on VHEE radiotherapy and provide a synthesis of the studies that have been published on various experimental and simulation works. We will also consider the potential for VHEE therapy to be translated into clinical contexts.

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The effects of high dose rates of ionizing radiations on solutions of iron and cerium salts

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1960.0082 ◽

1960 ◽

Vol 255 (1283) ◽

pp. 490-508 ◽

Cited By ~ 16

Keyword(s):

Hydrogen Peroxide ◽

Dose Rate ◽

Ferrous Sulphate ◽

High Dose ◽

Oh Radicals ◽

Dose Rates ◽

Reaction Zones ◽

Constant Dose ◽

Ceric Sulphate ◽

Ionizing Radiations

The electron beam generated by a 15 MeV linear accelerator has been employed to induce reactions in aerated aqueous solutions of 1 to 25 mM ferrous sulphate, and of 0⋅1 to 1 mM ceric sulphate. The radiation was delivered in pulses of 1⋅3 μ s duration and over a range of dose rates from 0⋅5 to 20000 rads/pulse. Radiation yields at constant dose rate were compared with the aid of a chemical dose monitor. A system of two thin, widely spaced, irradiation vessels was employed to determine the variation of yield of any one system over successive known ranges of dose rate. The yield of ferric sulphate in the iron system was found to decrease with increasing dose rate in the range 0⋅01 to 10 krads/pulse by an overall factor of 0⋅85, and was appreciably dependent on the initial concentrations of dissolved oxygen and of ferrous sulphate at high dose rates. Yields of hydrogen and of hydrogen peroxide were practically independent of dose rate. The observations have been interpreted on the basis of inter-radical reactions which occur when the reaction zones of neighbouring clusters overlap. The following reactions can account for all the data: OH + Fe 2+ → Fe 3+ + OH ¯ , (1) H + O 2 → HO 2 , (2) H + OH → H 2 O. (7) The values k 1 / k 7 = 0⋅0062, and k 2 / k 7 = 0⋅22 are reasonably consistent with the observations. In the ceric sulphate system the yield of cerous sulphate increases progressively over the range 0⋅01 to 10 krads/pulse by an overall factor of 1⋅4. The data accord with the view that at high dose rates OH radicals react with them selves ultimately to form hydrogen peroxide, in competition with their normal reaction with cerous sulphate.

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