Why the Search for Dark Matter Depends on Ancient Shipwrecks
aristarchus writes:
In a sort of a reversal of the problem that Clair Patterson had, wherein, as you will recall, his research was contaminated by environmental lead, originating in gasoline additives, researchers attempting delicate studies of very far away phenomena need shielding, namely lead, that is not contaminated by radioactivity.
Fine article available at The Atlantic.
In 2017, Chamkaur Ghag, a physicist at University College London, got an email from a colleague in Spain with a tempting offer. The year before, an emeritus professor at Princeton University, Frank Calaprice, had learned of old Spanish ships that had sunk off the New Jersey coast 400 or 500 years ago, while carrying a cargo of lead. Calaprice obtained a few samples of this lead and sent it off to Spain, where a lab buried within the Pyrenees tested its radioactivity. It was low: just what Aldo Ianni, the then-director of the Canfranc Underground Laboratory, was hoping for. Now that sunken lead was being offered to any physics laboratory willing to pay 20 euros per kilogram-a fairly high price-for it.
Lead is mined and refined all over the world, but that centuries-old lead, sitting in a shipwreck, has a rare quality. Having sat deep underwater since before the United States of America was born, its natural radioactivity has decayed to a point where it's no longer spitting out particles. For particle physicists, that makes it exceptionally valuable.
Source of radioactive contaminants in lead? Yes, you guessed it!
Take steel: It's an excellent shield from intruding vagabond particles-so much so that Fermilab, a particle-physics and accelerator laboratory in Illinois, has used tons of it in the past few decades to shield its own experiments, says Valerie Higgins, Fermilab's historian and archivist. That steel frequently came from decommissioned warships, many of which existed around the time of, or served in, the Second World War or the Korean War, including the Astoria, the Roanoke, the Wasp, the Philippine Sea, and the Baltimore.
The timing of those conflicts matters. At 5:29 a.m. on July 16, 1945, the first-ever nuclear-device detonation took place in the Jornada del Muerto desert, in New Mexico. The atomic age had begun, and with each subsequent nuclear fireball, more radioactive fallout was sprinkled over the world.
During the Cold War, that radioactive atmospheric contamination got effortlessly sucked into blast furnaces when steel was made, Duffy says. This infused the final product with radiation, making it unsuitable for many physics experiments.
Thus the market in sunken lead. And a conflict between astrophysics and archeaology. Ah, science!
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