Identification and Mitigation of Radioactive Backgrounds for Rare Event Search Experiments and underground science
Rare event searches and underground science have undergone considerable development over the last 3 decades, mostly dedicated to physics thematics such as the study of solar neutrinos, the search for dark matter and neutrinoless double beta decay. But more recently the study of the impact of cosmic rays and natural radioactivity on microelectronic components, on quantum circuits and even in cell biology is also growing.
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The cosmogenic activation of materials is the production of radioactive isotopes due to the exposure to cosmic rays. The origin of primary cosmic radiation is galactic and is mainly composed of protons (~87%), alpha-particles (~12%) and nuclei Li, Be, B, C, O and F. The kinetic energy of these galactic particles can extend up to 10^^20 eV reaching the surface of the Earth with significant energies. They interaction with the atmospheric components induces production of new particles: n, H, He, 7Be, 14C, 37Ar, 39Ar, ...
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The Neutron activation of materials is the production of radioactive isotopes in materials submitted to a high neutron flux.
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The radiopurity of materials is a crucial point for rare event search experiments. A central repository of material radiopurity measurements has been settled and is now available to the community. Experiments are invited to feed the database with they radioassay measurements.
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There is no single material that will stop all radiation or particles. The type and nature of a shield depends on the type and amount of radiation one wishes to attenuate or stop. Alpha particles can easily be stopped by a single sheet of paper and cannot penetrate the outer dead layer of the skin. To attenuate or stop neutrons, light materials with hydrogen atoms will be most effective. Whereas for gammas, high Z materials are best suited. In the context of rare event search experiments, the materials used for shielding must also fulfill drastic radiopurity conditions.
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Depending on the nature of the radiation to be detected and quantified ( α, β, γ, μ, ν ...) different techniques are used.
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Most of the underground laboratories have their own low background facility equipped with instruments able to quantify the radiopurity of materials.
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