The Radiolysis of Water Vapor at Very High Dose Rates. II. Isotope Effects in the Hydrogen Yield from H2O–D2O Mixtures

1973 ◽  
Vol 51 (24) ◽  
pp. 4056-4061 ◽  
Author(s):  
A. W. Boyd ◽  
C. Willis ◽  
O. A. Miller
Keyword(s):  
Water Vapor ◽  
Isotope Effect ◽  
Isotope Effects ◽  
High Dose ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
Dose Rates ◽  
Very High

The isotope effect in the formation of hydrogen has been measured for H2O–D2O mixtures (10–90% H2O, 0.5–1.0 mg ml−1, 412–138 °C) with and without 1 mol% SF6 at 2 × 1027 eV g−1 s−1. The values of α ((H/D) radiolytic hydrogen/(H/D) H2O–D2O) for the reactions of hydrogen atoms are in the range 3–6 varying with H/D ratio of the substrate. Consideration of possible mechanisms for these large α values leads to the conclusions that reaction of the hydrogen atoms to form hydrogen involves the substrate and that the species H3O may be formed as an intermediate.

Isotope effects in the gas phase radiolysis of H2S and D2S

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.

Radiolysis of Hydrogen Sulfide at Very High Dose Rates. The Effect of SF61

1971 ◽  
Vol 49 (10) ◽  
pp. 1677-1682 ◽  
Author(s):  
C. Willis ◽  
A. W. Boyd ◽  
O. A. Miller
Keyword(s):  
Hydrogen Sulfide ◽  
Low Dose ◽  
Single Pulse ◽  
Ion Pair ◽  
High Dose ◽  
Hydrogen Yield ◽  
Dose Rates ◽  
Absorbed Doses ◽  
Electron Pulses ◽  
Very High

Gaseous H2S has been irradiated with electron pulses from a Febetron 705 at a dose rate of ~2 × 1027 eV g−1 s−1. For single pulse experiments, the yield of hydrogen is G(H2) = 12.0 ± 0.5, independent of pressure from at least 350 to 1600 Torr. Addition of SF6 reduces the yield to G(H2) = 7.9 ± 0.3 which is fairly close to that observed for pure H2S at low dose rates. The reduction, ΔG(H2) = 4.1 ± 0.3, agrees very well with the ion pair yield based on a W value of 25.3 eV.In multi-pulse irradiations, for pure H2S, the yield falls off with dose giving a limiting yield close to G(H2) = 8.0. No similar fall-off is observed for H2S–SF6 mixtures. It is proposed that at high absorbed doses and at low dose rates, there is no contribution to the hydrogen yield from neutralization processes; and that this is due to neutralization of H3S+ by an ion of the type Sn− rather than a free electron.

The Radiolysis of Water Vapor at Very High Dose Rates. I. Hydrogen Yields from H2O, H2O–HCl, and H2O–HBr Mixtures

1973 ◽  
Vol 51 (24) ◽  
pp. 4048-4055 ◽  
Author(s):  
A. W. Boyd ◽  
C. Willis ◽  
O. A. Miller
Keyword(s):  
Water Vapor ◽  
Rate Constant ◽  
Pure Water ◽  
Second Order ◽  
High Dose ◽  
Oh Radicals ◽  
Dose Rates ◽  
Equivalent Rate ◽  
Very High

The plateau yields of hydrogen from the Febetron radiolysis of mixtures of water vapor with up to 8 mol% of HCl or HBr are G(H2) = 7.9 ± 0.2 and G(H2) = 4.6 ± 0.2 with 1 mol% SF6. These yields are consistent with G(H) = 7.45 in pure water vapor and G(H) = 4.15 in water vapor with SF6. In the Febetron radiolysis of pure water vapor at 2 × 1027 eV g−1 s−1 and densities of ~1 mg ml−1G(H2) = 1.65 + 0.05 from 164 to 190 °C. This yield is reduced to G(H2) = 0.90 ± 0.05 on the addition of 1 mol% SF6. Using a second order equivalent rate constant for the disappearance of the OH radicals in water vapor at 1 mg ml−1 of 2 × 1010 M−1 s−1 these yields are consistent with ate constant values for the reactions H + OH (+H2O) → H2O, OH + OH (+H2O) → H2O2, and H + H (+H2O) → H2, of 1.7 ± 0.1 × 1010 M−1 s−1, 1.5 ± 0.5 × 109M−1 s−1, and 3 ± 1 × 108 M−1 s−1, respectively.

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

Cancers ◽  
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.

The radiation chemistry of carbon monoxide at very high dose rates

1970 ◽  
Vol 48 (19) ◽  
pp. 3029-3033 ◽  
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.

Absorbed dose-to-water protocol applied to synchrotron-generated x-rays at very high dose rates

2016 ◽  
Vol 61 (14) ◽  
pp. N349-N361 ◽  
Author(s):  
P Fournier ◽  
J C Crosbie ◽  
I Cornelius ◽  
P Berkvens ◽  
M Donzelli ◽  
...  
Keyword(s):  
Absorbed Dose ◽  
High Dose ◽  
X Rays ◽  
Dose Rates ◽  
Absorbed Dose To Water ◽  
Very High

scholarly journals Feasibility Study of a Prostate Cancer FLASH Therapy Treatment With Electrons of High Energy

2021 ◽  
Author(s):  
Alessio Sarti ◽  
Patrizia De Maria ◽  
Battistoni Giuseppe ◽  
Micol De Simoni ◽  
Cinzia Di Felice ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Technological Development ◽  
High Energy ◽  
Planning System ◽  
Treatment Planning System ◽  
High Dose ◽  
Dose Rates ◽  
Very High Energy ◽  
Almost All ◽  
Very High

Abstract Prostate cancer is among the most common cancers in men and one of the leading causes of death worldwide. Different therapies are adopted for its treatment and generally radiotherapy with photons (RT) is the preferred solution in almost all cases. Up to now, in addition to photons, only protons have been implemented as alternative radiotherapy. The use of Very High Energy Electron (VHEE) beams (100-200 MeV) has been suggested in literature but the needed accelerators are more demanding, as far as space and cost are concerned, with respect to standard photon devices, with only limited advantages when compared to protons or other heavy ions. In this contribution we investigate how recent developments in electron beam therapy could reshape the landscape of prostate treatments. The VHEE Treatment Planning System obtained combining an accurate Monte Carlo (MC) simulation with a simple modelling of the FLASH effect (healthy tissues sparing at very high dose rates) is compared with conventional RT. The results demonstrate that FLASH therapy with VHEE beams of 70-130 MeV could represent a valid alternative to standard RT allowing a better sparing of the healthy tissues surrounding the tumour, in the framework of an affordable technological development.

scholarly journals Generation of ultrafast, transient, highly acidic pH spikes in the radiolysis of water at very high dose rates. Relevance for FLASH radiotherapy.

2021 ◽  
Author(s):  
Abida Sultana ◽  
Ahmed Alanazi ◽  
Jintana Meesungnoen ◽  
Jean-Paul Jay-Gerin
Keyword(s):  
High Dose ◽  
Acidic Ph ◽  
Cellular Functions ◽  
Spike Response ◽  
Dose Rates ◽  
Hydronium Ions ◽  
Circular Surface ◽  
Sparing Effect ◽  
Tissue Sparing ◽  
Very High

Monte Carlo multi-track chemistry simulations were carried out to study the effects of high dose rates on the transient yields of hydronium ions (H<sub>3</sub>O<sup>+</sup>) formed during low linear energy transfer (LET) radiolysis of both pure, deaerated and aerated liquid water at 25 °C, in the interval ~1 ps–10 μs. Our simulation model consisted of randomly irradiating water with <i>N</i> interactive tracks of 300-MeV incident protons (LET ~ 0.3 keV/μm), which simultaneously impact perpendicularly on the water within a circular surface. The effect of the dose rate was studied by varying <i>N</i>. Our calculations showed that the radiolytic formation of H<sub>3</sub>O<sup>+</sup> causes the entire irradiated volume to temporarily become very acidic. The magnitude and duration of this abrupt “acid-spike” response depend on the value of <i>N</i>. It is most intense at times less than ~10–100 ns, equal to ~3.4 and 2.8 for <i>N</i> = 500 and 2000 (<i>i.e.</i>, for dose rates of ~1.9 × 10<sup>9</sup> and 8.7 × 10<sup>9</sup> Gy/s, respectively). At longer times, the pH gradually increases for all <i>N</i> values and eventually returns to the neutral value of seven, which corresponds to the non-radiolytic, pre-irradiation concentration of H<sub>3</sub>O<sup>+</sup>. It is worth noting that these early acidic pH responses are very little dependent on the presence or absence of oxygen. Finally, given the importance of pH for many cellular functions, this study suggests that these acidic pH spikes may contribute to the normal tissue-sparing effect of FLASH radiotherapy.

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

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.

The X-radiolysis of water vapor containing methanol. Effects of some electron and hydrogen atom scavengers

1968 ◽  
Vol 46 (12) ◽  
pp. 1957-1964 ◽  
Author(s):  
R. S. Dixon ◽  
M. G. Bailey
Keyword(s):  
Nitrous Oxide ◽  
Water Vapor ◽  
Carbon Tetrachloride ◽  
Hydrogen Atom ◽  
Sulfur Hexafluoride ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
A Value ◽  
Ion Recombination ◽  
Positive Ion

The X-radiolysis of water vapor containing methanol at 125 °C and 1 atm pressure has been studied alone and in the presence of some electron and hydrogen atom scavengers. In water vapor containing methanol only, a plateau value G(H2) = 7.9 ± 0.3 is obtained at all methanol concentrations above 0.5 mole %. Addition of propylene drastically reduces this yield due to efficient scavenging of hydrogen atoms, and values for the total number of H atoms from all precursors g(H)t = 7,5 ± 0.2 and [Formula: see text] are deduced from the competition. An unscavengeable hydrogen yield g(H2) ~ 0.5 is also indicated in mixtures containing propylene. Nitrous oxide and sulfur hexafluoride are found to scavenge electrons efficiently in water vapor containing methanol and the number of hydrogen atoms arising from electron–positive ion recombination is estimated to have a value G = 2.2 ± 0.6. The number of hydrogen atoms arising from processes not involving electrons is g(H) = 5.2 ± 0.3. Carbon tetrachloride reacts efficiently with both electrons and hydrogen atoms, with k(H + CH3OH)/k(H + CCl4) = 0.085. Values of g(H) = 4.9 ± 0.5 and g(H2) = 0.8 ± 0.2 are deduced from mixtures containing carbon tetrachloride.

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