Monitoring bromide effect on radiolytic yields using in situ observations of uranyl oxide precipitation in the electron microscope.

During electron microscopy observations of uranium-bearing phases and solutions in a liquid cell, the electron beam induced radiolysis causes changes in the chemistry of the system. This could be useful for investigating accelerated alteration of UO 2 and can be also used to monitor radiolytic effects. Low concentrations of bromide in aqueous solutions are known to reduce the generation rate of H 2 O 2 during radiolysis and increase H 2 production. We deduced the presence of radiolytic H 2 O 2 by monitoring the formation of a uranyl peroxide solid from both solid UO 2 and a solution of ammonium uranyl carbonate at neutral pH. Additionally, the effect of bromine on water radiolysis was investigated through chemical modelling and in situ electron microscopy. By measuring the contrast in the electron microscopy images it was possible to monitor H 2 O 2 formation and diffusion from the irradiated zone in agreement with the models.