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Emerging Technology from the arXiv

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Superheavy Element 111 Found in Gold

Roentgenium-111 shouldn’t exist on Earth. Now a group of nuclear physicists claims to have found an ultra-stable version of it in gold.

  • December 2, 2010

Take a look at the periodic table and you’ll find that almost all the elements up to the atomic number 94 occur on Earth in relatively decent amounts. In addition, nuclear physicists can prepare samples of elements up to 104 because they form as by-products of the decay of other elements.

Beyond that, the so-called superheavy elements have to be made by hand, using particle accelerators to fuse nuclei together. In this way, physicists have fashioned elements with atomic numbers all the way up to 118. Atoms of these elements survive for only a fraction of a second before decaying, which is why they don’t occur naturally on Earth.

But these elements are more stable than physicists originally thought, leading to the prediction that there ought to be an “island of stability” for superheavy elements further up the periodic table.

That raises an interesting question: why don’t we see these elements on Earth? The answer, according to Amnon Marinov at the Hebrew University of Jerusalem, is that we do see them, but only in concentrations too small for most analytical techniques to detect. He’s even claimed to have found the superheavy element 122 in a sample of thorium, a story we looked at a couple of years ago.

Today, Marinov is back with a similar claim. He says that the superheavy element 111, also known as roentgenium, is chemically similar to gold and so ought to be found in tiny quantities in any lump of the glittering stuff. And now he says he’s found evidence of this.

His technique is to first concentrate the roentgenium in gold. He does this by heating gold to a temperature of 1127 degrees C, which is 63 degrees C above its melting point and leaving it in a vacuum. His thinking is that gold atoms ought to evaporate faster than roentgenium because they are lighter.

After two weeks, he took what was left and passed it atom by atom through a mass spectrometer to see what it was made of.

The results are an interesting mix. There’s plenty of stuff with an atomic mass of about 261, which roentgenium is expected to have. But Marinov can account for each peak close to 261. Combinations of gold and zinc, uranium and sodium, and thorium nitrogen and hydrogen, for example, all lie close.

But having discarded these peaks, he says he is left with one that corresponds exactly to roentgenium, proving its discovery.

That’s bound to be a controversial result. Measurements of the half life of the few atoms of roentgenium created in particle accelerators indicate it should decay in a gnat’s blink. And that means that any roentgenium that once existed on Earth should have long ago decayed into something else.

Marinov’s answer to this is that he’s found a new kind of nuclear isomer that is somehow much more stable than the plain vanilla roentgenium.

That’s not beyond belief but it is a big ask. And it will need independent confirmation from other groups before the nuclear physics community accepts it.

That won’t worry Marinov, who is no stranger to controversy. It’s fair to say that his claim to have found element 122 in thorium is disputed and not yet entirely accepted by the majority of his colleagues.

The discovery of roentgenium in gold is almost certain to trigger a similar response. So it’ll be interesting to see now whether anybody can repeat this result.

Ref: arxiv.org/abs/1011.6510: Enrichment of the Superheavy Element Rg in Natural Au

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