Everyday electrons

We made some in-studio lightning!
06 August 2019

Interview with 

Alex Thom, University of Cambridge


A lightning bolt in the sky


Most of us probably don’t have cathode ray tube TVs in our living rooms anymore - but electrons are still very much a part of our lives. If you’ve ever gotten a spark from a nylon jumper, that’s because of static electricity. It’s actually the same physics as a lightning strike! Katie Haylor and Izzie Clarke were joined by Alex Thom, a chemist at the University of Cambridge, to make some lightning, right in the studio...

Alex - So I'm going to demonstrate a process called triboluminescence is where you create light from mechanical force. And so I've got a roll of sticky tape called Duct tape and we're going to need to turn studio lights down just to see what's going to happen.

Katie - Izzie’s just about to do that now…

Alex -  So yes if you're going to try this at home you'll probably want to be in quite a dark room at night time and get your eyes very used to the darkness. So I'm basically just gonna peel this tape. I'm going to watch for some light coming out from where the tape meets the roll

[Alex peels the tape]

Alex - Any light visible there?

Katie - I mean I'm not 100 percent convinced I saw anything. I hate to be the bearer of bad news! Is it not dark enough?

Alex - It might not be dark enough in the studio. Unfortunately there's quite a lot of light in here.

Izzie -We tried our best, but when we're recording it's still quite light.

Katie - OK. So say you did have a dark room, say it's night time you’re at home you've turned the blinds down you turn the lights off - what's actually going on?

Alex - So you see a little band of blue light and that's where as the sticky tape comes apart from the roll, electrons are caught on one side or the other. So the electron gets stuck on one side and leaves a positive charge on the other. And as you pull that further away that electron gets further away from the positive charge and eventually zaps back to the other side the roll. And emits light during that process.

Katie - So by moving electrons around we can result with light?

Alex - Yeah that's exactly the same as you get in lightning in fact.

Katie - OK. So can we create different frequency light then?

Alex - Yes. So the conditions you do it in change the type of light. So it turns out if you do this in a vacuum, you can generate x-rays at the same time. And so there's a team of scientists in 2008 who did this and they had an automated un-roller and they generated x-rays and actually took an x-ray of a finger using using sticky tape.

Katie - So that was moving electrons apart, which we're going to take your word for it results in light. You've also got a banana and some salt on the table so what are you trying to do with this? I'm hoping it's not some sort of odd snack!

Alex - Alas no. So I've got here a banana which is in fact a miniature particle accelerator!

Katie - Eh?

Alex - Yeah! So this banana sitting in the studio is generating 15 electrons a second, creating them effectively, which is very different from what we did with the tape which was just moving them around. So inside the banana there's quite a lot of potassium atoms and some of those potassium atoms are unstable and they decay to a more stable nucleus which is calcium. And in that process they give out an electron.

Katie - And it's the electrons that you're detecting on the yellow box which I'm pretty sure is a Geiger counter?

Alex - Exactly yes. This Geiger counter I'm going to point at the banana and we can see if we can detect these electrons being created as we speak. Every time an electron gets into the detector it will give a click. So it's gonna be pointing at the air and not clicking very much.

Katie-  So if we just take a listen ………. nothing.

Alex - Yeah. There's not a lot there. Under maybe one every three seconds or something like that.

Katie - So is that what you would expect, because there is some background level of radiation, right?

Alex - Yes. So actually this is a significantly lower level of radiation than in my house. It's probably because of the walls.

Katie - So there's not very much going on in air in the air that is around us right now. So question is what happens when you put the detector on the banana? This Geiger counter is a  - there's a yellow box as I said and then there's a cable and something which looks like you've wrapped it in foil. Is that the actual detector?

Alex - Yes there's a tube called a Geiger-Muller tube that I've wrapped in foil to try and reduce the background getting into this tube.

Katie - And what's happening inside that box then, how does the detector work?

Alex - So every time an electron goes into the tube, it sends a shockwave of electricity through the cable into the box and that's just converted into a little click. And I've got a read out here and I can tell you how many clicks per second.

Katie - So you've got a little dial or something.

Alex - And it's currently less than 1.

Katie -  OK. That's reassuring. So let's see what happens with the banana then!

Alex - So as we point it to the banana …

[points the detector to the banana]

...there's a couple of clicks.

Katie - Oh yeah.

Alex - I'd say it's about the same it might even be slightly less.

Katie - Why would it be less?

Alex -  This banana is actually shielding the radiation that's coming from the studio, because it's more dense than the air. So yes it turns out this banana isn't sufficiently radioactive for us to detect. Thankfully in a way, it's not quite got enough concentration of potassium.

Katie - But you said a banana is a particle accelerator of sorts.

Alex - Yes. So it's these potassium nuclei inside that are actually firing out electrons pretty fast actually, a big fraction of the speed of light.

Katie - So the other culinary item you've brought with you is some low sodium salt...which you’ve just spilt all over the studio!

Alex - There's still of a lot of low sodium salt here.

Katie - Enough for the experiment right? So if it's low in sodium does that mean it's high in something else?

Alex - Yes. So they replace the sodium in the salt with potassium, so as to avoid you getting high blood pressure.

Katie - So it's this potassium we're hoping might change the game a little bit?

Alex - Exactly so this is the most concentrated source of potassium I think I could find in the home. So I'm going to put the Geiger detector onto this salt and we'll have to listen carefully. So here we go...

[multiple clicks]

Katie - That's definitely more frequent. What's the reading?

Alex - The reading’s about three and a half. So that's quite a lot more.

Katie - And how did that compare to the banana?

Alex -  The banana was about half. Oh okay.

Katie - Now it's not just the things you'll find in the kitchen that are radioactive. What kind of other radioactive sources exist?

Alex - Oh yes there are quite a lot. There even some around the home. So in your smoke detector there's an Americium source, which is used to detect whether or not there's smoke in the air and that that doesn't give out electrons that gives our alpha particles, in that case, which are helium nuclei.

Katie - So considering that bananas aren't very radioactive, we don't need to be worried about having too many bananas and having a radioactivity issue?

Alex - I think you would be unable to eat that many bananas. A truckload of bananas might just set off a radiation detector but it's still perfectly safe. You get far less from exposure to that than you would for example by taking a transatlantic flight.


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