At the time of writing this blog post, the Euro is doing quite well against the pound, but my intention is to get away from politics and back to science - you’ll all be pleased to hear.
Euro notes have a number of anti-forgery features, amongst them the use of europium in the printing ink. Europium is a metallic element in the lanthanide series and like all lanthanides it is fluorescent. Put a Euro note under UV light and it will fluoresce at a characteristic wavelength. Europium is rare and expensive and so why is this element used in Euros as opposed to any of the other lanthanides?
There are several reasons. Firstly the fact that it is rare in itself is a barrier to would-be forgers. Secondly, it is the most reactive of the lanthanides and therefore forms a range of compounds and complexes that can be used to formulate inks. Lastly, of course, I’m sure someone in the EU just thought it was appropriate - maybe a little amusing - to use the element named after Europe in its currency.
Europium has two naturally occurring isotopes 151Eu and 153Eu with the latter being slightly more abundant at 52%. Although Europium was discovered in 1901, recently in 2014, it was discovered that 151Eu was very slightly radioactive.
The half-life of 151Eu is 4.6 x 10 18 years - which is about 3-billion times longer than the age of the Universe. A kilogram of Europium emits about 2 alpha particles every 2-minutes, which in the scheme of things isn’t really very radioactive. (A kilogram of Europium costs around 1.35 million US$ by the way - 30 times the price of gold). A kilogram of carbon emits 14,000 beta particles per minute (due to the presence of very small amounts of naturally occurring radioactive 14C). The paper in the Euro is therefore far more radioactive than the ink.
Europium was discovered by the French chemist Eugène-Antole Demarçay by isolating it from contaminated samples of samarium. On balance therefore, I think it unlikely that Nigel Farage would be in favour of using it as an anti-forgery feature in the pound, but I’ve just slipped back into politics. My apologies.