Positrons from Bananas
Departments Research impact and institutes 9 November 2022
In the latest in our mini-series of posts about the work our scientists are carrying out at CERN, we speak to Will Bertsche. Will is a lecturer with the Accelerator Physics group in the Department of Physics and Astronomy at the University, as well as a lecturer in the Cockcroft Institute. We started by asking Will how he got involved with working on the Alpha experiment at CERN.
“When I started my graduate student career, I started in plasma physics. I was kind of interested in nonlinear dynamics, but also experimental physics. And at the time, the supervisor that I worked for, Joel Fajans, at UC Berkeley, was doing some interesting work with non-neutral plasmas and the nonlinearities associated with those plasmas. And halfway through my studentship, my supervisor got contacted by the folks who were forming the Alpha collaboration at CERN – sort of a spin out of a collaboration called Athena, which was one of the first antihydrogen collaborations. And the work was really in the wheelhouse of some of the work that Joel had done in the lab at Berkeley. And so we as a lab agreed to work with Alpha and got involved pretty early on in then making the full Alpha experiment. I spent basically the second half of my studentship working on this prototype experiment, and then incorporating the ideas and designs from that aspect of the prototype into the overall first version of the Alpha experiment that was built at CERN and started operating in about 2006.”
Bananas turn out to be a reasonably good source of positrons because they’re a good source of potassium… a banana produces about 15 positrons a second
We asked Will what the Alpha experiment actually involves
“We’re making antihydrogen by combining anti-matter electrons called positrons with anti-matter protons called antiprotons. Positrons are relatively easy to come by as anti-matter particles are concerned. You can get them from the radioactive decay of species you can just find naturally occurring on earth. In fact, bananas turn out to be a reasonably good source of positrons because they’re a good source of potassium and some small fraction of naturally occurring potassium is a radioactive isotope that produces positrons when it decays. So a banana produces about 15 positrons a second. Okay, that’s not very practical for experiments; we use salts that have been activated in a reactor to get a good flux for ourselves. But that’s relatively straightforward. The connection to CERN is that antiprotons are more difficult. If you want antiprotons on earth, you need to produce them with a relatively high energy interaction. And in order to create that kind of reaction, you need accelerators. And so CERN’s not the only institute in the world that can and has produced antiprotons, but they are the unique facility in the world right now that produces antiprotons that are low enough energy for experiments like Alpha to trap those antiprotons, and then use them for other sorts of experiments.”
In one of our recurring questions, we asked Will whether he was frustrated with the way the work that’s taking place on the LHC is sometime reported in the mainstream media.
“It’s tricky, right? That this is what gets headlined in the tabloids. And I think when people have legitimate questions about the kinds of issues raised like this – for example, the black holes question – I think the community takes that sort of thing pretty seriously. And there was a really compelling scientific response to whether we should be concerned with micro black holes or something like that being produced at the LHC. And I think that’s an appropriate scientific response, so when the public raises those sorts of issues they can be addressed.
The salesperson just flat out refused to give us a quote because they thought that the work CERN was doing was evil
“There are more challenging kinds of things that that we do receive that don’t really have easy rational answers, shall we say. There are definitely people who don’t understand what CERN is and the way we work as scientists. And they’re concerned that we’re somehow developing secret technologies, which we definitely aren’t! I mean, Alpha as an experiment is entirely funded by public money. All of our results are fully accessible by the public. So that’s kind of how we operate; we don’t have some hidden agenda that that we’re working towards. And the only thing you can do is try and educate the public about it.”
It seems as though there may still be a lot of work to do in that area.
“I do have a funny story about this, where we were upgrading part of our spectroscopy experiment. We were in the process of improving our clocks; one of the limitations of our experimental results at the moment is how well we can tell time at our experiments, because we’re basically comparing time according to anti-hydrogen with time according to the rest of the matter universe on some level. And so we’re improving our clocks, which are pretty complicated devices – they involve all sorts of technologies and microwaves and lasers and electronics. And so you buy components, you plug them in, you get things operating to do what you want to do. And we had a contact with a company that has a good reputation of producing certain kinds of equipment. And so we got in touch and we wanted to get a quote to buy this equipment from them. And the salesperson just flat out refused to give us a quote because they thought that the work CERN was doing was evil!
“So, I mean, that’s certainly the first time I’ve seen that kind of negative press, you know, cycle back in in a way that has impacted our work. It means that we just have to find a different manufacturer for what we were trying to do. It was very strange – we even wrote the company and asked them if this was, you know, some kind of a joke. And they were like, no, this really isn’t a joke. And the European distributor confirmed to us that the people at the head of the company really believed this. This wasn’t just some kind of one off view by some random salesperson. So anyway, that was strange. We’re not even in the category of experiments that get accused of doing things like making black holes! So that was kind of a one off.”
Thanks again to Will for agreeing to speak to us, and giving us his valuable insight into the work he does at CERN. He gives much more detail in the full interview, which you can listen to below:
Transcript of the audio discussion with Will Bertsche (PDF document)
If you’d like to read more about the work our scientists are doing at CERN, you might like to read the previous articles in this series, where we talked about building equipment for the LHC here at the University, and the work Chris Parkes is leading on the LHCb experiment – one of the four main experiments, along with Alpha, that take place on the LHC. And don’t forget to join us next time, when we’ll be talking to Marco Gersabeck.
