Salt has very low gamma radiation. Salt is a good insulator. Salt is radio-pure. Salt is an excellent substance in which to encase yourself if you want to study weakly interacting massive particles. But salt is also highly plastic. Salt flows over time. It creeps around. It sags. If you cut a chamber out of a seam of halite with 3,000 feet of bedrock above it, that chamber will slowly distort. The ceiling will dip, the sides will bulge. Gravity wants that space back. So the scientists working in the Boulby laboratory know they are operating in a temporary zone, with limited years of safe life.
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