Dating a saint
Two towns in Italy lay claim to relics from St. Francis of Assisi–pieces of clothing and an embroidered cushion from his deathbed.
But one of those relics cannot be authentic because it was manufactured decades after the saint's death in 1226, according to physicists who tested them in May.
Contrary to popular fiction, particle accelerators can't take people back in time. But they can provide time stamps for clothing, books, and other ancient items that contain carbon.
Scientists at Italy's Laboratory of Nuclear Techniques for Cultural Heritage in Florence examined three relics tied to St. Francis, an aristocrat who took a vow of poverty, founded the Franciscan Order, and became the Roman Catholic patron saint of animals.
Examinations conducted at the lab found that a tunic and embroidered cushion housed in the Church of St. Francis in Cortona dated from the time when the saint was alive. However, another tunic from the Basilica of Santa Croce in Florence was made decades later.
The method the researchers used, known as accelerator mass spectrometry, requires much smaller samples than other forms of radiocarbon dating. This allowed the scientists to take five to seven samples of woolen fabric from the tunics, each smaller than one square centimeter; the more samples tested, the more accurate the results would be.
The swatches were treated to extract small pellets of graphite, a form of carbon. These pellets were exposed to cesium ions in an accelerator, releasing carbon isotopes that are counted by a detector. By measuring the ratio of carbon 14 to carbon 12–a delicate undertaking, since there is only one carbon 14 for roughly a trillion carbon 12s–the researchers determined the age of the fabric and discounted Florence's claim to holding this particular piece of history.
Tona Kunz
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