CERN scientists turn lead into gold

The age-old dream of turning lead into gold has finally been realised…if only for a brief moment. It was not the work of ancient alchemists, who actually boiled up urine trying to do this, but instead physicists at CERN, who did it by using the world's most powerful particle collider. But, before you grab your shovel and a swagbag and head for Geneva, it’s not going to spark a new gold rush: the amount they’re making is measured in picograms! Nonetheless, it is a milestone, and could also help to shed light on how elements form across the universe. Marushka Soobben sat down with Cambridge University theoretical physicist Ben Allanach on the banks for Cam to hear how the team behind the discovery did it…

Ben - So atoms, if you remember, have a dense nucleus and then lots of space and they have some electrons around the outside. Protons are different kinds of particle. They've got positive electric charge and gold has 79 protons in its nucleus and lead has 82.

Marushka - So basically we lose three protons and we get gold.

Ben - If you manage to shave off three protons off a lead nucleus, you get a gold nucleus. And in modern scientific terms, that's really what we're talking about. Once you've got a positive nucleus, it's easy to get the right electrons to fill up the rest of the atom and so on.

Marushka - Okay, so the nucleus is the important part of this experiment. And how did the scientists at CERN manage to do this?

Ben - One or two months every year they fill the beams that they collide at CERN with lead nuclei and they fire them at each other at very close to the speed of light, really high energies. So you get these two lead nuclei. Often they collide and that's actually the main science purpose of doing this. Occasionally they kind of just miss each other. And that's where this interesting result came from.

Marushka - And what is that called when they just miss each other?

Ben - You could call it a glancing collision. But the important thing is this electromagnetic dissociation. So basically, because these protons have positive charge in the nucleus, the nucleus has a very strong electric field around it. And if the other one glances close to it, the electric field is so strong, it can upset one of them and it can lose a proton or two or three in this case. And so what they wanted to do is to see how often it lost a proton or two or three, which would change the nuclei from being lead ones to either thallium, mercury or gold nuclei, depending if it's one, two or three protons. So you detect how many protons come off and you infer that some of the lead nuclei have been changed to, for example, gold nuclei.

Marushka - Is this viable in any way?

Ben - The calculations from the experimental measurement tell us that since 2015, so over the last 10 years, CERN has produced 10 to the minus 11 grams of it, which is a lot less than a gold grain of sand. So you certainly wouldn't use CERN to produce gold. In no way is it scalable or practicable economically or otherwise.

Marushka - So why do we bother with doing experiments like this if it's going to create basically dust?

Ben - There are deep scientific questions these experiments are trying to answer, and the lead into gold was just kind of an interesting byproduct of trying to answer those scientific questions. So what you're doing, colliding lead nuclei together, is you're recreating the conditions that were around in the very early universe, in fact, like something around a billionth of a second after the Big Bang. There you don't have nuclei and atoms, everything's shoved together and it's too hot and too dense. And so you're trying to recreate, in the centre of the collision, a little bit of space where you've got a lot of particles and it's very dense and hot so you can measure and constrain that scenario and try and work out what was going on in the early universe.

Marushka - So there's a lot of implications for this work outside of just making a little bit of gold.

Ben - Yeah, that's right. In particular, you could ask, well, what about these glancing collisions? Why are they interesting and why did they write a paper? And what they really want to understand is this business about the high electric fields. Because it turns out you can use those to make measurements of interest and constrain particle physics if you can understand them well enough. So this is like a sort of precursor to that, to try and understand these very intense electric fields and make sure that you know what's going on with them. And then you can use the rest of the data to constrain what's going on with the particle physics. I mean, the lead into gold made a nice new story and it's kind of interesting in its own right. The big work of the science is in other areas really.