Nuclear physics and Roman archaeology just don’t mix, or so you would

think. But researchers at the National Institute of Nuclear Physics in Padua,

Italy, and a team of archaeologists have found a common goal: to raise 1500

ingots of lead from a Roman freighter which sank off the coast of Sardinia

more than 2000 years ago.

The physicists, Gianni Fiorentini and Ettore Fiorini, want the lead

for experiments that are of critical importance in particle physics and

cosmology. Donatella Salvi, an archaeologist working with the Italian authority

for artistic and historical heritage, wants to know more about the Mediterranean

lead trade in the first century BC.

The ship was discovered two years ago near an island called Mal di Ventre,

so-named because of the high wind that plagues the area. It was modified

to carry lead and is the only one of its type known.

The physicists want the ancient lead for a practical reason. Lead is

the best material for shielding delicate experiments which detect minute

amounts of radiation, for example from the unusual kinds of radioactivity

associated with double beta decay, or from the rare interaction of neutrinos

– the ghost-like particles that are emitted from the Sun and pass through

the Earth unheeded. Another experiment requiring shielding is the detection

of particles of so-called dark matter – the material believed to hold the

Universe together.


Such experiments are usually carried out deep underground in specially

built installations, such as the Gran Sasso Laboratory near Rome. Here,

1400 metres of solid rock protect the detecting apparatus from high-energy

cosmic rays raining through the atmosphere. Small amounts of radioactive

materials in the rocks themselves, however, can interfere with the experiments,

so the detector has to be surrounded by an additional lead shield.

Commercial lead has only tiny amounts of radioactive contaminants such

as lead-210, but even this is enough to affect very sensitive experiments.

However, the half-life of lead-210 is 22 years, which means that lead excavated

a long time ago would have lost most of its radioactive component. In fact,

physicists have sometimes relied on lead from old cannonballs for their

experiments.

Lead that is 2000 years old would be expected to contain virtually no

radioactive isotopes at all. The physicists, when they tested a small portion

of a salvaged ingot, found this was the case.

What will the archaeologists get out of the salvaging project? Apart

from the 300 million lire (£135 000) from the institute, the physicists

have agreed to analyse the ingots to establish their geological origins

and set up a database for archaeological studies. Each ingot has a manufacturer’s

mark and the researchers hope that the data will help them to map the trading

routes that once served a flourishing Roman metallurgical industry.