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Shroud of Turin: Tests May Give It an Age

October 26, 1986|LEE DYE | Times Science Writer

Seven research institutions around the world, including three in the United States, will participate in an unprecedented project next year that should precisely date the Shroud of Turin and possibly end a centuries-old controversy.

The shroud, which many believe to have been the burial cloth for Jesus Christ, shows the image of a man who died by crucifixion.

In 1978, the shroud was the subject of a wide range of scientific studies, many of them based on chemical analyses. But those studies, designed merely to determine the authenticity of the image, failed to turn up evidence that would disprove the authenticity.

And until now, the Vatican has resisted pressure to determine the age of the shroud through radiocarbon dating because the technique would have destroyed much of the shroud. But that danger has been lessened with the development of new techniques that can yield reliable results from only a tiny fragment of the shroud.

Tests Results Long Awaited

The test, long awaited by scientists and religious leaders alike, could prove that the artifact is far too young to have been the burial cloth.

However, even if the results show that the shroud dates back to the time of Christ, it will not prove that it was indeed the burial cloth, or that the image on the 14-feet-by-4-feet piece of linen is that of Jesus.

Thus, seven labs are in the position of being able to prove a negative, but not a positive. The results are expected to be announced in early 1988.

"What will come out of our effort will be the age of the cloth," said Douglas Donahue, a nuclear physicist at the University of Arizona, one of the participating institutions.

The others are Oxford, Rochester (N.Y.) and Zurich universities, and the Centre pour Faibles Radioactivites in France, Harwell in the United Kingdom and the Brookhaven National Laboratory in New York.

Until a few years ago, even radiocarbon techniques would have destroyed much of the shroud because samples to be dated must first be burned so that the carbon can be extracted. And that required large samples in order to determine the ratio between carbon 14 and other carbon isotopes, one of nature's most reliable time clocks.

But a new technology has evolved, using a nuclear accelerator to bombard a sample with a beam of cesium ions, giving the carbon atoms a negative charge so that they can be collected with an electric field. The carbon atoms are then fired through the accelerator and into a target of argon atoms. That gives the carbon 14 atoms a positive charge so that they can be drawn off with a magnet from the other negatively charged carbon isotopes.

Device Counts Isotopes

The magnet diverts the carbon 14 isotopes to a device that counts them.

In nature, carbon 14 is created when nitrogen atoms in the atmosphere are struck by cosmic rays from outer space. The carbon 14 becomes part of the carbon dioxide in the atmosphere, which is taken up by all living things.

As long as the animal or plant remains alive, the percentage of carbon 14 in its tissues remains constant, but upon death it no longer takes up carbon dioxide, and the various types of carbon isotopes decay at different rates. Thus the percentage of carbon 14 reveals the time at which the plant or animal ceased taking up carbon dioxide.

The Shroud of Turin is made of linen, and the ratio of carbon 14 to carbon 12 and 13--which are carbon atoms of a different weight, called isotopes--will tell scientists when the plant fibers were turned into cloth.

The task will be especially difficult because only about one out of every trillion carbon isotopes is carbon 14.

Finding a Marble

"It's like if you had an acre of blue marbles, three feet deep, with one red marble mixed in with the blues," said Paul E. Damon, a University of Arizona geochemist and principal co-investigator with the university's Laboratory of Isotope Geochemistry. "Your job would be to find the red marble."

The University of Arizona's accelerator was completed in February of 1982, and it immediately proved its value by showing that two skulls found in California were far younger than scientists had believed, thus saving anthropologists the trouble of trying to explain how humans could have been in California 30,000 years before Homo sapiens appeared in the Old World.

After that, scientists at Arizona and elsewhere began seeking permission from the Vatican to date the Shroud of Turin.

The British Museum last spring sent out 18 linen samples of known age to labs that had expressed an interest in dating the shroud. Seventeen of the 18 results were on the money, Damon said. The 18th sample, tested by a Zurich university, apparently had been contaminated, he added.

Vatican Agreement Seen

The impressive results led the the Pontifical Academy of Sciences to agree to the test. The Vatican, which has custody of the shroud, still has not given the effort its blessing, but Damon believes that it is only a formality.

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