A novel method for measuring the radiolysis yields of water adsorbed on ZrO<inf>2</inf> nanoparticles

© 2020 Elsevier Ltd A novel method has been implemented to prepare metal oxide nanopowders covered with known quantities of adsorbed water; we subsequently studied the γ-radiolysis of ZrO2 nanopowders covered with H2O layers. H2 yields from the adsorbed water radiolysis are of importance in multiple industrial contexts – the nuclear industry being a prime example. Measured H2 yields at water coverages of just below and above one monolayer are around 350 times greater than for neat water, but these yields decrease rapidly with increasing water loading of the ZrO2 nanoparticles, approaching the yield of bulk water at coverages of tens of water layers. The observed plateau of the yields at 0.5 to 2.0 monolayers coverage can be explained by the ease with which electronic excitations in the ZrO2 can be transferred across the interface to the first one or two adsorbed water layers. However, with increasing water loading, energy transfer to water layers further away from the interface becomes less efficient, and above ~30 water layers, most of the water is not affected by any exciton formation in the ZrO2

Phenotypic characterisation of Shewanella oneidensis MR-1 exposed to X-radiation

Biogeochemical processes mediated by Fe(III)-reducing bacteria such as Shewanella oneidensis have the potential to influence the post-closure evolution of a geological disposal facility for radioactive wastes and to affect the solubility of some radionuclides. Furthermore, their potential to reduce both Fe(III) and radionuclides can be harnessed for the bioremediation of radionuclide-contaminated land. As some such sites are likely to have significant radiation fluxes, there is a need to characterise the impact of radiation stress on such microorganisms. There have, however, been few global cell analyses on the impact of ionizing radiation on subsurface bacteria, so here we address the metabolic response of S. oneidensis MR-1 to acute doses of X-radiation. UV/Vis spectroscopy and CFU counts showed that although X-radiation decreased initial viability and extended the lag phase of batch cultures, final biomass yields remained unchanged. FT-IR spectroscopy of whole cells indicated an increase in lipid associated vibrations and decreases in vibrations tentatively assigned to nucleic acids, phosphate, saccharides and amines. MALDI-TOF-MS detected an increase in total protein expression in cultures exposed to 12 Gy. At 95 Gy, a decrease in total protein levels was generally observed, although an increase in a putative cold shock protein was observed, which may be related to the radiation stress response of this organism. Multivariate statistical analyses applied to these FT-IR and MALDI-TOF-MS spectral data suggested that an irradiated phenotype developed throughout subsequent generations. This study suggests that significant alteration to the metabolism of S. oneidensis MR-1 is incurred as a result of X-irradiation and that dose dependent changes to specific biomolecules characterise this response. Irradiated S. oneidensis also displayed enhanced levels of poorly crystalline Fe(III) oxide reduction, though the mechanism underpinning this phenomenon is unclear

Validation and investigation of reactive species yields of Geant4‐ DNA chemistry models

Purpose: Indirect biological damage due to reactive species produced in water radiolysis reactions isresponsible for the majority of biological effect for low linear energy transfer (LET) radiation. Modelingwater radiolysis and the subsequent interactions of reactive species, as well as track structures, isessential to model radiobiology on the microscale. Recently, chemistry models have been developedfor Geant4-DNA to be used in combination with the comprehensive existing physics models. In thecurrent work, the first detailed, independent, in silico validation of all species yields with publishedexperimental observations and comparison with other radiobiological simulations is presented. Additionally,the effect of LET of protons and heavier ions on reactive species yield in the model wasexamined, as well as the completeness of the chemical reactions following the radiolysis within thetime after physical interactions simulated in the model.Methods: Yields over time of reactive species were simulated for water radiolysis by incident electrons,protons, alpha particles, and ions with various LETs using Geant4 and RITRACKS simulationtools. Water dissociation and recombination was simulated using Geant4 to determine the completenessof chemical reactions at the end of the simulation. Yield validation was performed by comparingyields simulated using Geant4 with experimental observations and other simulations. Validation wasperformed for all species for low LET radiation and the solvated electron and hydroxyl radical forhigh LET ions.Results: It was found that the Geant4-DNA chemistry yields were generally in good agreement withexperimental observations and other simulations. However, the Geant4-DNA yields for the hydroxylradical and hydrogen peroxide at the end of the chemistry stage were found to be respectively considerablyhigher and lower than the experimentally observed yields. Increasing the LET of incidenthadrons increased the yield of secondary species and decreased the yield of primary species. Theeffect of LET on the yield of the hydroxyl radical at 100 ns simulated with Geant4 was in good agreementwith experimental measurements. Additionally, by the end of the simulation only 40% of dissociatedwater molecules had been recombined and the rate of recombination was slowing.Conclusions: The yields simulated using Geant4 are within reasonable agreement with experimentalobservations. Higher LET radiation corresponds with increased yields of secondary species anddecreased yields of primary species. These trends combined with the LET having similar effects onthe 100 ns hydroxyl radical yield for Geant4 and experimental measurements indicate that Geant4accurately models the effect of LET on radiolysis yields. The limited recombination within the modeledchemistry stage and the slowing rate of recombination at the end of the stage indicate potentia