Twenty years ago, an amateur scuba diver swimming off the coast of Oristano in Sardinia found a navis oneraria magna – a 36-m Roman ship dating back more than 2000 years, to between 80 and 50 BC – whose cargo consisted of a 1000 lead forms. These were recovered with help from Italy’s National Institute of Nuclear Physics (INFN), which at the time received 150 of the lead bricks. Now, INFN is to receive a further 120 bricks to complete the shielding for the Cryogenic Underground Observatory for Rare Events (CUORE), in INFN’s Gran Sasso National Laboratory (LNGS).
Image credit: Il Nuovo Saggiatore/Società Italiana di Fisica di Bologna and INFN.
INFN has received the lead bricks from the National Archaeological Museum of Cagliari in Sardinia. The bricks, together with the ship that transported them, had remained in the sea for two millennia, during which time the albeit low original radioactivity of one of the radionuclides, 210Pb, decreased by approximately 100,000 times. The 210Pb, which has a half-life of 22 years, has by now practically disappeared from the ancient Roman lead.
The parts of the bricks that contain inscriptions will be removed and conserved, whereas the remainder will be cleaned of incrustations and melted to construct a shield for the international CUORE experiment. Moreover, researchers from INFN will perform precise measurements on the lead (and possibly on the copper that was also found on the ship) to study the materials used in the Bronze Age.
The lead bricks were made available as the result of a collaboration involving INFN, its facilities in Cagliari and the Archaeological Superintendency of Cagliari, as well as with the support of the General Directorate of Antiquity. As part of this joint operation 20 years ago the INFN contributed 300 million lira for the excavation of the ship and the recovery of its cargo.
The bricks, which weigh about 33 kg each and are 46 cm long and 9 cm wide, will be used to shield the CUORE experiment. This collaboration is seeking to discover the extremely rare process of neutrinoless double-beta decay, which would allow researchers not only to measure directly the mass of neutrinos but also to determine whether or not they are Majorana particles (i.e. particles and antiparticles are one and the same). The detector will be based on an array of nearly 1000 tellurium-dioxide bolometers, cooled to about 10 mK.
