Ancient Shipwreck to Aid Ghostly Neutrino Search

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You wouldn’t think a sunken ship from 2000 years ago could hold the key to the success of a neutrino detection experiment, except perhaps in a Hollywood movie, or a NOVA special on Jacques Cousteau. But sometimes truth really is stranger than fiction. Scientists with the Cryogenic Underground Observatory for Rare Events (CUORE), a neutrino observatory buried under the Gran Sasso mountain in Italy, hit the motherlode when archaeologists discovered a Spanish ship off the coast of Sardinia, filled with lead that dates back two millennia.

Yes, lead. Really, really old lead. That might not seem very exciting to you, but for CUORE scientists, it’s a godsend. They use lead (also copper) as a shielding material for their neutrino detection materials. See, neutrinos — dubbed “ghost particles” because they so rarely interact with everything (billions course through you every second) — are extremely difficult to detect, in part because their signals can be obscured by things like cosmic rays, and the natural radioactivity in rocks, for example.

CUORE is looking for an even rarer event, known as neutrinoless double-beta decay. Among other things, such an observation would provide a handy means of directly calculating the mass of a neutrino (which is very, very small — so small that for decades physicists believed neutrinos had no mass).

Alas, there are also trace amounts of radioactivity in the very materials that are supposed to shield the experiments from interference — the radioactive isotope lead-210, in the case of contemporary lead ingots. But if you have lead that is 2000 years old, that radioactive isotope has pretty much disappeared. Unfortunately, lead that old is quite a rare find. US scientists working on the IGEX experiment lucked out a few years ago when they snagged from 450-year-old lead from a sunken Spanish galleon.

That’s why the discovery of this new sunken ship is so exciting to nuclear physicist Ettore Fiorini, who finessed some key financing from the Italian National Institute of Nuclear Physics so that archaeologists could salvage the vessel — in return for for a bunch of that ancient lead. And there’s rather a lot of it, apparently. While most such ships were merely lined with lead, this particular vessel was actually carrying lead as its cargo, so the find “multiplies by many times the quantity of ancient lead available in the world,” according to Fiorini.

The CUORE scientists have received a couple of batches of the precious ancient lead so far, which will be cleaned and melted down to make a shield for the experiment. CUORE should be fully operational in two to three years. And if they succeed in observing neutrinoless double-beta decay, and applying that knowledge to determine the “ghost particle’s” mass, it will be partly thanks to that very old lead — and the archaeologists who shared the bounty of their find.

Image: A diver recovers lead ingots from a sunken Roman vessel (Il Nuovo Saggiatore/Società Italiana di Fisica di Bologna)

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