科学美国人60秒:用碳同位素验证威士忌的真假

This is Scientific American's 60-second Science, I'm Eliene Augenbraun.
"It came to our attention a few years ago that there were fraudulent whiskeys on the market."
Gordon Cook of the Scottish Universities Environmental Research Center.
"Scotch whiskey is Scotland's product, and we felt that being a radiocarbon laboratory in Scotland, we should take a lead on this."
Scotch whiskey is made from barley, which absorbs carbon dioxide from the air as it grows. Most of the carbon is carbon-12. But a small percentage is the radioactive isotope carbon-14, which decays at a constant, known rate— and has therefore long been used to "carbon-date" biological samples.
"Then, in the early 1950s, we had the start of the atmospheric weapons test, and these produce carbon-14. By 1960, you were twice the natural level. And '63—there was a test ban treaty, so '63 was the maximum. Since then, the level in the atmosphere has decreased as the radiocarbon goes into the biota and the oceans."
So unusually high levels of carbon-14 are associated with barley grown during the years when nuclear testing was widespread.

There's obviously a lot of money in whiskey. And some classics get bought not as imbibements but as investments. Last October, a 60-year-old 1926 bottle was auctioned off for $1.9 million.
To make sure that the stuff inside bottles of Scotch whiskey matches what's on the labels, Cook and his colleagues looked at levels of the carbon-14 in the drink. They calibrated levels of the radioactive variant of carbon in more than 200 different single-malt Scotch whiskey samples of known ages. The researchers then compared those levels to eight whiskeys claiming to have been bottled from 1847 to 1978.
"We haven't found any whiskeys purported to be from the 19th century that are genuine."
Because those allegedly 19th-century bottles contained material clearly produced during the nuclear-testing era. The study is in the journal Radiocarbon.
Cook hopes these verification techniques will help keep the whiskey business true to the words of Robert Burns: "Here's a bottle and an honest friend."
For Scientific American's 60-second Science. I'm Eliene Augenbraun.