Radiolysis of cyclohexane with perfluorocyclohexane at very high dose rates

1970 ◽  
Vol 48 (3) ◽  
pp. 501-503 ◽  
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.

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

1970 ◽  
Vol 48 (22) ◽  
pp. 3463-3472 ◽  
Author(s):  
Clive Willis ◽  
P. E. Bindner
Keyword(s):  
Carbon Dioxide ◽  
Dose Rate ◽  
Total Pressure ◽  
Ionic Species ◽  
High Dose ◽  
Dose Rates ◽  
Low Concentrations ◽  
Neutralization Process ◽  
Ionic Reactions ◽  
Very High

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.

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.

scholarly journals The FLASH effect depends on oxygen concentration

2020 ◽  
Vol 93 (1106) ◽  
pp. 20190702 ◽  
Author(s):  
Gabriel Adrian ◽  
Elise Konradsson ◽  
Michael Lempart ◽  
Sven Bäck ◽  
Crister Ceberg ◽  
...  
Keyword(s):  
Oxygen Concentration ◽  
Underlying Mechanism ◽  
Oxygen Depletion ◽  
Therapeutic Window ◽  
High Dose ◽  
Dose Rates ◽  
Conventional Dose ◽  
Oxygen Concentrations

Objective: Recent in vivo results have shown prominent tissue sparing effect of radiotherapy with ultra-high dose rates (FLASH) compared to conventional dose rates (CONV). Oxygen depletion has been proposed as the underlying mechanism, but in vitro data to support this have been lacking. The aim of the current study was to compare FLASH to CONV irradiation under different oxygen concentrations in vitro. Methods: Prostate cancer cells were irradiated at different oxygen concentrations (relative partial pressure ranging between 1.6 and 20%) with a 10 MeV electron beam at a dose rate of either 600 Gy/s (FLASH) or 14 Gy/min (CONV), using a modified clinical linear accelerator. We evaluated the surviving fraction of cells using clonogenic assays after irradiation with doses ranging from 0 to 25 Gy. Results: Under normoxic conditions, no differences between FLASH and CONV irradiation were found. For hypoxic cells (1.6%), the radiation response was similar up to a dose of about 5–10 Gy, above which increased survival was shown for FLASH compared to CONV irradiation. The increased survival was shown to be significant at 18 Gy, and the effect was shown to depend on oxygen concentration. Conclusion: The in vitro FLASH effect depends on oxygen concentration. Further studies to characterize and optimize the use of FLASH in order to widen the therapeutic window are indicated. Advances in knowledge: This paper shows in vitro evidence for the role of oxygen concentration underlying the difference between FLASH and CONV irradiation.

Primary yields and mechanism in the radiolysis of gaseous ammonia

1969 ◽  
Vol 47 (16) ◽  
pp. 3007-3016 ◽  
Author(s):  
C. Willis ◽  
A. W. Boyd ◽  
O. A. Miller
Keyword(s):  
Dose Rate ◽  
Rate Constant ◽  
High Dose Rate ◽  
Radical Reactions ◽  
Gaseous Ammonia ◽  
High Dose ◽  
Ammonia Vapor ◽  
Radical Product ◽  
Very High

Ammonia vapor has been irradiated with single pulses of electrons at a very high dose rate (1027 eV g−1 s−1) with a Febetron 705. At this dose rate radical–product reactions are not significant. In pure ammonia, hydrogen, nitrogen, and hydrazine are produced and the yields found at 1027 eV g−1 s−1 are: G(H2) = 3.58 ± 0.08; G(N2) = 1.00 ± 0.05; G(N2H4) = 0.58 ± 0.05. The yields are independent of pressure from 1 to 5 atm and of temperature between 20 and 200 °C. Above 250 °C the yields of all three products increase significantly and this is due to reaction [1] competing with radical–radical reactions.[Formula: see text]A rate constant for this reaction has been determined,[Formula: see text]Product yields have been measured for ammonia–propene mixtures. These yields have allowed determination of the primary radiation yields GNH = 0.74; [Formula: see text]; GH = 4.8; and G(−NH3) = 5.4.

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.

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