At the Facility for Rare Isotope Beams (FRIB), the interactions between heavy-ion beams and the beam-dump water will create a plethora of valuable radionuclides that can be accessed by a technique known as ‘isotope harvesting’. With the dissipation of such large amounts of energy, not only nuclear, but also radiolysis reactions are induced. From the generated radiolysis products, hydrogen, hydrogen peroxide, and oxygen, exhibit sufficiently long lifetimes to accumulate in the irradiated water and possibly affect the harvesting chemistry. Here we examined the formation of radiolytic H2, H2O2, and O2 during a high intensity proton beam irradiation of a flowing-water isotope harvesting target and the experimental results were compared to a simulation. The simulation was developed in Python, and it kinetically models the chemical reactions occurring in the homogeneous radiolysis phase during proton irradiation of the flowing-water target. Both, the experiment as well as the simulation demonstrate significantly lower H2, H2O2, and O2 quantities than predicted by the primary radiolytic yields. This undermines the considerable impact of homogeneous phase reactions on the chemical composition of the water within the high-beam intensity regime. Additionally, the simulations suggest that the bulk outcome could be represented by a simplified steady state model. Comparable conditions at the upcoming FRIB allow a translation of the steady state model to predict the hydrogen, hydrogen peroxide, and oxygen content within the entire isotope harvesting system.

Radiolysis in a flowing-water target during high intensity proton irradiation

ACS Spring 2022

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