Building new, heavy elements

28 March 2017

Interview with 

Rodi Herzberg, University of Liverpool

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Element structure

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As well as the naturally occurring elements, scientists can also make “artificial” atoms that wouldn’t exist normally. And this is how, last year, we were able to add a further four new elements, known as “super-heavy” elements, to the periodic table. They’re the biggest atoms known to exist.  Chris Smith was joined by Rodi Herzberg, a Professor of Super-heavy Nuclei at the University of Liverpool to discuss how to make these atoms in the first place.

Rodi - What you do in order to get to these very heavy elements, the neutron capture mechanism that Marialuisa just described no longer works up to that heavy mass. So you start out by two lighter nuclei and you start to fuse them together. So you throw them together as often as you can and you hope that, eventually, two of them will manage to fuse together and form one of these superheavy elements.

Chris - So you basically give them a huge amount of energy and hope that they collide hard enough that it will squeeze the two different nuclei together and you get the sum total of the two nuclei - the cores of both those two individual atoms adding together?

Rodi - Indeed. Yet this is a very delicate process because, if you give it just a little bit too much energy, then they become so unstable that they will immediately split apart again, so it has to be very, very finely balanced.

Chris - How many atoms of these new elements have actually been made?

Rodi - Let me take one of them - element 113 (nihonium). Of that element three atoms have been made by the Japanese group. Don’t laugh! Not only that but it took them about nine years to produce the third one.

Chris - Goodness. How do you actually detect when you’ve made a new atom of nihonium, for example?

Rodi - It’s a bit gruesome because you detect them by watching them die. The alpha decay that has been discussed previously, is a very characteristic way for the nucleus to die to decay to a different one. If you measure those decays, then you can get a very characteristic sequence of alpha decays that you don’t know. And finally, the same nucleus ends up in a couple of alpha decays that you do know and those give you then an anchor point, each of a particle is two protons and two neutrons, so you can do the math and work back upwards to what you originally must have had.

Chris - So by watching really carefully you’re measuring these radioactive decays and you’re seeing the particles coming off. So you know something is decaying and if you add up all those things, and you work out what you end up with, you can add them all back together to work out what you must have started with, and then you know you’ve discovered a new element potentially?

Rodi - Indeed.

Chris - But if they're so unstable that they only hang around long enough to fall apart in a fraction of a second, and three atoms have been made in nine years, why are we bothering to make these things?

Rodi - Because just the fact that you can make them teaches us an awful lot about nuclei. There are many, many places where you cannot do experiments so you need to have a very good understanding of what the binding forces inside a nucleus, inside a very complicated system like a nucleus are, and the best way to test this is if you go to very extreme systems.

Just because three atoms of this configuration of protons and neutrons actually were living long enough that we could detect them and do some physics with them, that means that our theoretical models have to be able to get that right and that’s the big challenge. If they can do that right, then they can also understand how the elements are made in stars. How the nuclear waste that we may want to incinerate can proceed. All of that comes indirectly from these.

Chris - Could we also use them as stepping stones? Even though they may be individually short is it possible that you could leapfrog off one of them if you quickly add something else to it and make an even bigger element, you make something where the nucleus is stable and it won’t immediately fall apart, and then you’ve got some exciting new chemical you can do something really, really impressive with?

Rodi - I think you can already do some impressive chemistry with some of them. For example, thaumium or with einsteinium people had little microscopic vile of einsteinium in their hand that they could do experiments with. It’s a question of quantity and if you increase your capability to create more, better beams, better targets, then you can make more.

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