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John Gamel asked:
What's the most expensive element on Earth? I'm reasonably sure it's not gold, maybe platinum or palladium.
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Graihagh Jackson put John's question to chemist Mark Lorch, from the University of Hull...
Mark - Plenty of materials are extremely expensive. There are drugs such as soloris which costs a whopping $700,000 for a yearís treatment. There are chemicals that have high social costs through drug abuse or pollution. But strictly speaking, none of these are elements. They're mixtures of elements bound together known as molecules or minerals.
Graihagh - Ahh, so they're not strictly elements. That narrows down our search just a little. So, weíre clear though. What exactly is an element, Mark?
Mark - Elements themselves are something that canít be chemically broken down into a simpler substance. Of course, they're all nicely laid out on the periodic table or indeed in song. There's antimony, arsenic, aluminium, selenium, and hydrogen and oxygen, and nitrogen and uranium, etc. So, being a chemist, I'm going to use that definition of an element.
Graihagh - Okay, so weíre looking for an element, but what do we mean when we say expensive?
Mark - Well, we canít live without oxygen or carbon or a host of other elements which makes them invaluable. But to make things slightly simpler, I think Iíll stick to purely monetary values.
Graihagh - Let the fight beginÖWeighing in at just 12 on the atomic mass scale, itís lightweight underdog, carbon.
Mark - It might cost pennies when itís graphite in your pencil, but turn it into the best diamonds and it might fetch $100,000 for a gram.
Graihagh - That is a hefty price tag! What else is a contender?
Mark - Astatine Ė itís radioactive. The half-life of a few hours and so, it decays as quickly as itís produced. The result is that there's probably less than 10 grams of naturally occurring astatine on the whole of the earth. But astatine still isn't the rarest member of the periodic table, not if we take into account man-made elements. That accolade probably goes to livermorium, made by bombarding heavy atoms together causing them to briefly fuse into the new element. Only a handful of atoms have ever existed and with the half-life of 61 milliseconds, they donít hang around for very long either. But whilst these are fabulously expensive to manufacture, there's no commercial reason to do so.
Graihagh - What does that leave us with as our champion?
Mark - Itís another man-made element but a useful one. With applications ranging from initiating nuclear reactors to radio therapy treatments for some cancers, but it doesnít come cheap. You also need to set aside a cool $27 million for just 1 gram.
Graihagh - And the winner by knockout is californium!
I cannot get a transcript of the show but I would assume it is antimatter that costs an awful lot to produce syhprum, Mon, 6th Jul 2015
Top of the league must be anti Hydrogen a vast amount of money has been spent to produce a few atoms syhprum, Tue, 7th Jul 2015
Not an element, admittedly, but back in the 1970's I bought some specialist subminiature thin-film thermistors which cost 400 times as much as moondust per gram.