Over the past few weeks some commentators in the UK have been complaining that there has been too much news coming too quickly. And yet in the midst of all the political and economic turmoil there was a science story that made the headlines. This is rare enough at the best of times and so to see science reported in the middle of a news maelstrom was particularly pleasing. The headline was “Helium Discovery Game Changer”
Helium is a gas that most will know from floating party balloons and the old gag of taking a lungful and sounding like Mickey Mouse (that joke never grows old). Notwithstanding fun at parties, helium is also important for running technology that requires low temperatures such medical magnetic resonance imaging (MRI) or nuclear magnetic resonance spectroscopy. The Large Hadron Collider also relies on very large quantities of helium as does the manufacture of semiconductors. Those semiconductors are pivotal in running the internet and so helium played a role in the very fact that you are reading this blog on-line. Helium is, in fact, a vital commodity to our modern technology.
Helium is the second most abundant element in the universe (after hydrogen) but here on Earth over the past few decades its supply has been rather limited. It’s a very light gas that’s not held by Earth’s gravity and so seeps off into space leaving the atmosphere with an abundance of around only 0.0005%. It is therefore not feasible to extract helium from the atmosphere. The major supply of helium on Earth comes as a byproduct of the natural gas industry, particularly from wells in Texas. The problem is that those supplies are now dwindling. The situation has been exacerbated in recent years by increased demand, particularly as MRI centres have spread across the globe.
Fans of the TV series Big Bang Theory, will remember Sheldon and Leonard having to obtain helium on the black market (season-9, episode-6). Supplies in places have indeed been sufficiently bad that a black market in helium may not be entirely fictional.
So why is helium, as opposed to any other gas, so important? It has the lowest boiling point of any element at -268.9 oC, which is just 4.25 oC above absolute zero. By contrast, hydrogen has a boiling point of -252.9 oC but is of course dangerous stuff to handle. Liquid nitrogen is also commonly used as a coolant as it’s abundantly available from the atmosphere. It’s boiling point however is -195.8 oC - that’s 73 oC higher than helium and so it’s uses are more limited.
But fear not, a new deposit of helium has been discovered in the Tanzanian East African Rift Valley. The deposit has been estimated to be around 1.5 trillion litres. In contrast, the average MRI needs about 1,700 litres and so it’s likely to last some considerable time. So how did this deposit of helium get there? Helium is actually generated continuously in the rocks of planet Earth but the gas is not necessarily trapped in a way that can be accessed. And this brings me to an interesting historical point.
I have an original copy of Frederic Soddy’s 1909 book called "The Interpretation of Radium". This was at time when Rutherford and his co-workers (of which Soddy was one) were beginning to understand the inner workings of the atom. The book is fascinating not so much for what was known at that time but for what was not known. The book has so many accounts where the researchers were balanced on the edge of great discoveries but they had not quite joined all the dots together. In his book Soddy discusses the production of helium from radium. He hypothesised that helium was a byproduct of radioactive decay and he set up an experiment to capture and measure its rate of production (see Figure). At that time however, the details of how helium might be a product of radioactive decay remained elusive.
Today we understand the process of alpha-decay, where a heavy isotope ejects two protons and two neutrons, in other words a helium nucleus, as it transmutes into a lighter element. A number of isotopes in the Earth’s crust (238U for example) undergo alpha-decay which leads to the production of helium. To get deposits of helium that can be drilled and accessed, the gas needs to be trapped in non-porous rock. The new deposits of helium were found by first looking for regions were helium was likely to be formed from alpha-decay and then, by using seismic imaging techniques, searching for geological conditions that might then form underground reservoirs.
Deposits of helium might be more abundant than were first thought and over time it’s likely more will be discovered. The problems of helium supply are not over quite yet however, as it will take time to establish the infrastructure necessary to extract the helium, process and liquify it. Nevertheless, this is definitely a step in the right direction and good news for science as well as fun at parties.