Roman lead for neutrino physics

Somewhen between 80 B.C. and 50 B.C. a Roman ship sank off the coast of Sardinia. Its cargo, more than 33 tons of lead, was recovered in 1988. Today this metal is used to shield neutrino detectors at Grand Sasso laboratory, located under 1,400 meters of (Italian) rock.

Recently mined lead always contains a small 'contamination' of the lead isotope Pb-210 which is (after some intermediate steps) a decay product of Radon-222. (Radon-222 itself is a radioactive gas produced via the Uranium/Radium decay chain.)

The problem is that Pb-210 is radioactive with a half live of 22 years. It converts via a beta-minus decay into Bi-210. Therefore recently mined lead cannot be used to shield the highly sensitive neutrino detectors.

Thus the neutrino physicists at Gran Sasso were happy to receive about 4 tons of 2,000 years old lead, where the Pb-210 content has decayed below the threshold where it is measurable in the background. Read the full story on nature.com.