Relaxation processes in solid methane pre-irradiated with an electron beam

Savchenko, E. V.; Kirichek, O.; Lawson, C.R.; Khyzhniy, I. V.; Uyutnov, S. A.; Bludov, M. A.

doi:10.1016/j.nimb.2018.06.031

Cited by 12 publications

(3 citation statements)

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“…[9]. Various types of ionizing radiation were used to study the radiation behavior of methane and methane-rich ices-ions [10][11][12][13][14][15][16][17][18][19], electrons [20][21][22][23][24][25][26][27][28][29] and photons [26,[30][31][32][33][34][35].…”

Section: Introductionmentioning

confidence: 99%

“…According to Carpenter's model [37], all recombination processes in solid methane moderators proceed in one stage and are controlled by the same activation energy for defect diffusion. However, commissioning tests of the ISIS TS2 solid methane moderator, in which a "burp"-like effect was observed [40], and the study of relaxation phenomena in solid methane preirradiated with an electron beam [28], led to the conclusion that the radiolysis defect recombination process happens in two stages, at different temperatures, and is therefore controlled by two different activation energies. Modifying Carpenter's approach, Kirichek and coauthors implemented two different types of radiation defects (H atoms and CH 3 radicals), with different recombination rates and thermal activation energies [40].…”

Section: Introductionmentioning

confidence: 99%

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Matrix-Assisted Processes in CH4-Doped Ar Ices Irradiated with an Electron Beam

Bludov,

Khyzhniy,

Uyutnov

et al. 2023

Methane

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The relaxation processes induced by exposure of the Ar matrices doped with CH4 (0.1–10%) to an electron beam were studied with a focus on the dynamics of radiolysis products—H atoms, H2 molecules, CH radicals, and energy transfer processes. Three channels of energy transfer to dopant and radiolysis products were discussed, including free charge carriers, free excitons and photons from the “intrinsic source” provided by the emission of the self-trapped excitons. Radiolysis products along with the total yield of desorbing particles were monitored in a correlated manner. Analysis of methane transformation reactions induced by free excitons showed that the CH radical can be considered a marker of the CH3 species. The competition between exciton self-trapping and energy transfer to the dopant and radiolysis products has been demonstrated. A nonlinear concentration behavior of the H atoms in doped Ar matrices has been established. Real-time correlated monitoring of optical emissions (H atom and CH3 radicals), particle ejection, and temperature revealed a nonmonotonic behavior of optical yields with a strong luminescence flash after almost an hour of exposure, which correlated with the explosive pulse of particle ejection and temperature. The connection of this phenomenon with the processes of energy transfer and recombination reactions has been established. It is shown that the delayed explosive ejection of particles is driven by both the recombination of H atoms and CH3 radicals. This occurs after their accumulation to a critical concentration in matrices at a CH4 content C ≥ 1%.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Matrix-Assisted Processes in CH4-Doped Ar Ices Irradiated with an Electron Beam

Bludov,

Khyzhniy,

Uyutnov

et al. 2023

Methane

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“…In Savchenko's experiments a thin solid methane layer was irradiated at a low temperature of 4 K. The temperature of the substrate was then slowly increased whilst recording a number of parameters. The main conclusion of the experiments was that the recombination of radiation defects happens in two stages [6,7]. It was assumed that the first stage, occurring at low temperatures between 10 K to 30 K, is driven by recombination of light species such as atomic hydrogen, protons and electrons.…”

Section: Introductionmentioning

confidence: 99%

Solid methane moderators: Thermodynamics and chemistry

Kirichek

Lawson

Draper

et al. 2020

JNR

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The unique properties of solid methane enable the conversion of hot, energetic neutrons into cold neutrons, with an efficiency approximately 3.5 times that of liquid hydrogen based moderators. However, practical applications of solid methane in neutron moderators turned out to be much more challenging than initially expected. Exposure of solid methane at low temperatures to neutron radiation leads to a build-up of radiolysis products in the solid methane matrix. Accumulation of defects beyond some critical number can result in a spontaneous self-accelerated recombination process, which in combination with the expansion of hydrogen built up in bulk solid methane during irradiation, was believed to be responsible for the moderator’s breakdown. Here we present results of our thermodynamic model, based on the theory of thermal explosion. Our model agrees well with the test data obtained using methane moderators developed at the IPNS neutron source, based at Argonne National Laboratory and the data acquired during commissioning of the ISIS Target Station 2 solid methane moderator. We also discuss the products of radiolysis reactions generated by exposure of the condensed methane to neutron radiation. The succession of radiolysis reactions may lead to the production of long chain hydrocarbons, which can contaminate the moderator system and significantly reduce efficiency of the heat-exchanger. The possible solutions for cleaning moderators using targeted solvents are considered. In the conclusion we give some practical recommendations, based on our simulation results and operational experience.

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