Tuesday, 2 March 2010

The new alchemists

One of the cool things doing nuclear physics is that it has realised the old alchemists' dream of turning lead into gold - or indeed any element into any other. While one of my colleagues has genuinely turned lead into gold, some of the most exciting work in nuclear physics comes from trying to make new elements.

The chemical elements start with element 1 - Hydrogen - with one proton in the nucleus, then on to element 2 - Helium - with two protons and so on. The heaviest element that you can dig out of the earth (in trace amounts) is Plutonium, with 94 protons. Beyond lead (element 82) all known nuclei are unstable against decay into lighter nuclei with characteristic lifetimes ranging from tiny fractions of a second to many trillions of years. As one gets, though, to heavier and heavier elements, the lifetimes get shorter and any nuclei heavier then plutonium that might have existed on the Earth have long decayed. This doesn't stop us trying to make new elements in the laboratory, though, to better understand the forces between neutrons and protons, and to try to understand what isotopes may have been made in nuclear reactions in stars.

These "superheavy" elements are made by colliding two lighter nuclei together and hoping that they fuse together. One then looks for the alpha particles that come from the decay and the resulting residual nucleus which one can hopefully identify as a known nucleus. Indirectly, by studying the decay chain, one gets a "genetic fingerprint" for the original superheavy nucleus. Recently, however, a group based at the GSI facility in Germany has actually measured a superheavy nucleus' mass directly, rather than by inferring it from the decay. By trapping it in a magnetic field and observing how fast it oscillates round the trap, one can determine its mass very accurately. Knowing the mass is important, as it is a measure of the stability of the nucleus. This helps us point to the possibility that there is a more stable region of superheavy nuclei inaccessible to experiment as yet, but containing nuclei long lived enough to make an appreciable amount of material from.

The work is published in Nature, and the IoP's Physics World blog has already reported it. It's perhaps not as earth-shattering, but before the Nature paper appeared, a PhD student of mine, and myself submitted a theoretical paper on the likely appearance of especially superheavy nuclei with very large numbers of neutrons. Fingers crossed the referees will return with positive comments!


  1. Heh, I remember doing a spring project on the exact subject back in Surrey, using neural networks. Good to see Darmstadt are still working on it, I wonder what scientists from Dubna have to say though!

  2. Should you have published in Nature then? Will these nuclei have any funky uses? What do you think they'll be called?

  3. Stavros - and you wrote a nice literature review of superheavy nuclei too, if I remember correctly!

    Natasha; perhaps I should have tried Nature. As for the names of the new nuclei, they'll be named by the experimental group that discovers them, not by a theoretician who predicts them. If I had any influence, and if my predictions are correct, then maybe I'd go for tensorium, since I think it sounds quite funky, and because my paper suggests that the tensor force will give stability to a region of nuclei not considered before.

    As for funky uses... I'm not sure. Perhaps as a tracer; they would give a unique signal as there wouldn't be any natural contaminant.

  4. Tensorium's a great name! Nicely geeky