Throughout the 1950s, the US, the Soviet Union, and others tested thermonuclear weapons in the Earth’s atmosphere. Those tests released vast quantities of radioactive material into the air and triggered fears that the nuclear reactions could ignite deuterium in the oceans, thereby destroying the planet in a catastrophic accidental fireball. Atmospheric tests ended in 1980 when China finished its programme, but the process has left a long-lasting nuclear signature on the planet. One of the most obvious signatures is cesium-137, a radioactive by-product of the fission of uranium-235. After release into the atmosphere, cesium-137 was swept around the world and found its way into the food supply in trace quantities. Such addition is rarely welcomed. But in 2001, the French pharmacologist Philippe Hubert discovered that he could use this signature to date wines without opening the bottles.
The technique immediately became a useful weapon in the fight against wine fraud—labelling young wines as older vintages to inflate their price. Such fraud can be spotted by various types of chemical and isotope analysis—but only after the wine has been opened, which destroys its value. Cesium-137, on the other hand, allows non-invasive testing because it is radioactive. It produces distinctive gamma rays in proportion to the amount of isotope present. Dating the wine is a simple process of matching the amount of cesium-137 to atmospheric records from the time the wine was made. That quickly reveals any fraud. Indeed, if there is no caesium-137, the wine must date from after 1980.
There is one blip in this record, though. The Chernobyl disaster in 1986 bathed much of Europe, and other parts of the world, in a radioactive cloud that increased atmospheric levels of cesium-137 again. Hubert and colleagues can see this blip in their data from wines. And that raises an interesting question about the Fukushima disaster of 2011, an accident of Chernobyl proportions caused by a meltdown at the Fukushima nuclear power plant in Japan following a huge earthquake and tsunami. It released a radioactive cloud that bathed North America in fissile by-products. Is it possible to see the effects of the Fukushima nuclear disaster in California wines produced at the time?
Today we get an answer, thanks to a study carried out by Hubert and a couple of colleagues. “In January 2017, we came across a series of Californian wines (Cabernet Sauvignon) from vintage 2009 to 2012,” said Hubert and company. This set of wines provides the perfect test. The Fukushima disaster occurred on March 11, 2011. Any wine made before that date should be free of the effects, while any dating from afterwards could show them. The team began their study with the conventional measurement of caesium-137 levels in the unopened bottles. That showed levels to be indistinguishable from background noise. But the team was able to carry out more-sensitive tests by opening the wine and reducing it to ash by evaporation. This involves heating the wine to 100 degrees Celsius for one hour and then increasing the temperature to 500 degrees Celsius for eight hours. In this way, a standard 750-millilitre bottle of wine produces around four grams of ashes. The ashes were then placed in a gamma-ray detector to look for signs of cesium-137. Using this method, Hubert and his colleagues found measurable amounts of caesium-137 above background levels in the wine produced after 2011. “It seems there is an increase in activity in 2011 by a factor of two,” conclude the team. That probably won’t be very useful for fraud detection in California wine—the levels of cesium-137 are barely detectable, and even then, only if the wine is destroyed. But the result does show how nuclear disasters can have unexpected consequences long after the fact.
Credit: Emerging Technology From The arXiv for MIT Technology Review, 19 July 2018.