Welcome to the tenth instalment of the Element of the Month – a regular feature on the Radleys blog. As usual, we chose our element of the month by using a random number generator to produce a figure between 1 and 118 – the number of elements in the periodic table (so far!). This month, terbium (Tb), atomic number 65, was selected. Terbium – The Key Facts Terbium is a silvery rare-earth metal. It’s soft, ductile and malleable. One of the lanthanide series, terbium is sandwiched between gadolinium (Gd) and dysprosium (Dy). It doesn’t naturally occur as a free element, but terbium is part of many minerals, such as gadolinite, euxenite, xenotime and monazite. A Few Fascinating Facts about Terbium Terbium was first identified by Swedish chemist Carl Gustaf Mosander in 1843, who detected its oxide it as an impurity in yttria (mainly yttrium oxide, Y₂O₃). Yttria takes its name from Ytterby, as it was derived from a mineral (ytterbite, now renamed gadolinite) discovered in a mine near this small Swedish village. Terbium too is named after Ytterby, as are erbium (Er), yttrium (Y) and ytterbium (Yb). Three more elements – thulium (Tm), gadolinium (Gd) and holmium (Ho) – were also first found there. So for such a tiny location, Ytterby is arguably the most important place in the periodic table! Though it was discovered as an element in 1843, pure terbium was not isolated until ion exchange methods were introduced in the 20thcentury. Terbium is possibly most famous for the bright green (or yellow) luminescence of Tb3+ ions when excited by the correct wavelength energy. This emission has been put to use in a number of applications, such as TV screens and low-energy light bulbs. Terbium’s green glow can help fight counterfeiting – it’s used in Euro notes and can be detected under UV light, together with blue from thulium ions (Tm3+) and red from europium ions (Eu3+). From banknotes to biology, terbium is also useful as a probe. NASA has developed a method to detect bacterial endospores with terbium, to make sure no pathogenic microorganisms secretly hitch a ride to space. Back down to Earth, fluorescence from terbium can also reveal endospores in soil. Other biological applications include studies of protein structure, DNA and RNA assays, drug analysis, and in-vitro imaging. A radioisotope of terbium (terbium-161) could even be used to kill cancer cells. The most fun use of terbium is to turn all sorts of surfaces into speakers! This is through its inclusion in the alloy Terfenol-D, which is magnetostrictive, meaning it changes shape (expands/contracts) in a magnetic field. Although originally developed by the US Naval Ordnance Laboratory (NOL) for sonar systems, now the mini Soundbug speaker can easily be purchased by anyone for hours of fun. You can even transform your skull into a speaker? In a more commercial application, Whispering Windows draw in amazed passers-by with music emitted from shop windows. So that’s terbium – from screens to spending to space to speakers, this element may not be one of the most famous. But we’re sure you’ll agree it’s certainly interesting. Join us next month, when we’ll be giving neptunium the well-deserved Element of the Month treatment.