NOBEL INGOTS

Lingotti 201630 lead ingots of Ancient Rome left Cagliari on Monday, 18 January on their last journey to the Gran Sasso National Laboratories (LNGS) of the National Institute for Nuclear Physics (INFN). After two thousand years under the sea, in the hold of a Roman ship which sank off the coast of Sardinia, their new home will be the bowels of a mountain, under 1,400 metres of rock of the Apennine range. The consignment ceremony of the Roman lead - the result of an agreement between INFN, which funded the excavation works of the wreck and recovery of its cargo, and the Sardinia Archaeology Authority, with the approval of the Ministry of the Cultural Heritage and Activities and of Tourism (MIBACT) - was held at the National Archaeological Museum of Cagliari. "The use of the Roman lead ingots represents an exemplary case of cooperation between the institutions, aimed at exploiting the national archaeological heritage and leading-edge scientific research, such as that on neutrino physics, in 2015 awarded the Nobel prize", explained Fernando Ferroni, INFN President. The project for the recovery the submerged ingots is the result of cooperation between INFN, the Sardinia Archaeology Authority and the Universities of Cagliari and Milan Bicocca. Subsequently, cooperation between INFN and the Universities of Cagliari, Sassari and Milan Bicocca allowed accurate measurements to be made in order to determine the chemical composition of the ingots. "Thanks to the very high technology instruments at LNGS, archaeometric analysis was possible using the isotopic ratios method, identifying the Roman mine of Sierra de Cartagena, from which the lead was extracted about two thousand years ago. In the coming months it will be possible to carry out more detailed studies", affirmed Stefano Ragazzi, LNGS Director. "The Roman lead, leaving Sardinia for LNGS, has unique and exceptional characteristics. Its recovery, the associated archaeological studies and its use for the INFN experiments not only bind together two apparently distant worlds, but are an example of the success, which is not isolated, of the cooperation between INFN, Sardinian Universities and the local Institutions", underlined Alberto Masoni, Director of the INFN section in Cagliari. "The University of Sassari is proud to contribute to this endeavour and to work with scientific institutions such as INFN, a world leader in these research fields. Another example of how in our university there are researchers able to be at the top of leading-edge research - affirmed Massimo Carpinelli, Rector of the University of Sassari -. I would like to thank the members of the research team that are carrying out the studies on the chemical composition of the ingots. The large amount of data collected through neutron activation and measurement of the ratios between the stable lead isotopes is at the service of the scientific community, engaged in the long process of archaeometric analysis and interpretation". The agreement between INFN and the Sardinia Archaeology Authority envisages the opportunity to use the 30 ingots, with an overall weight of almost one ton, preserving all their characteristics of an archaeological nature for archaeometric research, as suggested by UNESCO. “This lead - affirmed Ettore Fiorini, a physicist at the University of Milan Bicocca and designer of the CUORE experiment - is a precious material, with an important scientific, as well as archaeological, value for shielding the equipment for the search for rare events. This, in fact, must be a material which is totally free of radioactive contamination. Modern lead - explained Fiorini - in fact contains weak radioactive contamination due to the isotope 210, with a half-life of approx. twenty-two years. Hence the idea of using the lead from the Roman ship which, since it was produced two thousand years ago, no longer contains radioactive isotopes". CUORE is an experiment designed to study the properties of neutrinos and, in particular, an extremely rare phenomenon, called double beta decay without neutrino emission. This process has never been observed to date, and to do this physicists need extremely pure ambient conditions, in particular very low radioactivity. Hence the idea - proposed by Ettore Fiorini, carried out by the University and the INFN section of Milan Bicocca and the implementation of which has been followed in all its steps by LNGS - to provide CUORE with a special "shield", created thanks to the fusion of the lower part of the lead ingots. Lead, being a very dense material and with a high atomic number is, in fact, excellent for shielding from radiation. The Roman ship The ship was discovered by chance around 1990 by an amateur diver off the coast of Oristano, opposite the island now called Mal di Ventre, in the municipality of Cabras, a mile or so from the shore. It is a navis oneraria magna, a Roman ship 36 metres long which, over two thousand years ago, between 80 and 50 BC, was carrying about two thousand lead ingots, only half of which recovered. The ship came from the mine of Sierra of Cartagena, today in Spain, and was probably headed for Rome. According to archaeologists, it was specialised in the transport of lead for military and construction purposes. In its hold, in fact, on a floor made of copper, there were about two thousand lead ingots, along with urns of various types, anchors, on-board equipment and everyday objects. Archaeologists believe, given the position of the anchors placed at the bow, and the ingots still partly stacked, that the ship sank without suffering any particular trauma, probably at the initiative of the captain and his crew, to prevent the precious cargo ending up in enemy hands. The lead Each lead ingot is 46 cm long and 9 cm high and weighs about 33 kg. In Roman times, lead was a by-product of silver mining and represented an important market for its many uses. It was, in fact, widely used to make everyday objects, from water pipes (fistulae), such as those of ancient Pompeii, to weights and cinerary urns, in the production of bronze coins, as well as for the "acorns" of slingers, balls that were thrown by soldiers with slingshots on the battlefield. Over 200 of these projectiles were found on the sunken ship. Molten lead was also used in construction to hold together blocks of stone. Archaeologists have been able to reconstruct the origin of the precious Roman cargo. Each lead ingot has, in fact, its trademarks inscribed, such as "Caius and Marcus Pontilieni, sons of Marcus", "Quintus Appius, son of Caius", and "Carulius Hispalius. These were families of Italian origin that carried out mining activities in Spain. The CUORE experiment and the Majorana neutrinos The experiment at LNGS has been designed to discover a rare physical phenomenon, called double beta decay without neutrino emission. This is a process according to which, inside a nucleus, two neutrons are transformed into two protons, emitting two electrons and two antineutrinos. In double beta decay without neutrino emission, there is, in fact, no neutrino emission, since one of the antineutrinos has been transformed into a neutrino. The Standard Model envisages that neutrinos are excluded from this transformation. But if, as hypothesised in the 30s of the last century by the physicist Ettore Majorana from Catania, neutrinos and antineutrinos were two manifestations of the same particle, like the two sides of the same coin, the transition between matter and antimatter would then be possible. This phenomenon, albeit highly rare, may have been common in the primordial universe immediately after the Big Bang, and have determined the prevalence of matter over antimatter. CUORE is the result of the international cooperation of approx. 157 scientists from 30 institutions in Italy, USA, China, Spain and France. For INFN, the Milan Bicocca, Bologna, Genoa, Padua and Rome La Sapienza sections and the INFN Gran Sasso National Laboratories in Frascati and Legnaro are taking part.

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