Ep. 315: Particle Accelerators

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Female Speaker: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Fraser Cain: Astronomy Cast episode 315, particle accelerators. Welcome to Astronomy Cast, our weekly facts based journey through the cosmos where we help you understand not only what we know but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville and the director of CosmoQuest. Hey, Pamela. How you doing?
Pamela Gay: I’m doing well. How are you doing, Fraser?
Fraser Cain: Good. For those of you listening on the podcast feed, it’s been a few months since we’ve been recording but now, we’re back to our fall schedule.
Pamela Gay: It hasn’t been a few months. It’s been a month and a half.
Fraser Cain: Yeah. And now, we’re back to our fall schedule and you’re teaching people in the class and teaching people through the podcastings.
Pamela Gay: Something like that.
Fraser Cain: Something like that. So good. Well, did you have a good summer?
Pamela Gay: Yeah. I went all the places.
Fraser Cain: Yeah, I know. You were in Europe. You were in New Zealand. I feel like I didn’t go – well, I went to the Penny Arcade Expo and that’s it.
Pamela Gay: I went to Dragon Con.
Fraser Cain: You went to Dragon Con. Did you extract any audio from Dragon Con?
Pamela Gay: No. I turned out that Astronomy Cast got left off of the feeds and off of the schedule and yeah, it just devolved.
Fraser Cain: Oh, well. Oh, well. No problem.
Pamela Gay: The other one I could have recorded, we’d already done so it is what it is.
Fraser Cain: It is. Usually you like to come back with some audio but not this year but maybe next year.
Pamela Gay: Yeah.
Fraser Cain: Okay, cool. So let’s get rolling.
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Fraser Cain: So who knew that destruction could be so informative? Only by smashing particles together with more and more energy can we truly tease out the fundamental forces of nature. Join us to discover the different kinds of particle accelerators, both natural and artificial, and what questions they can help us answer. So particle accelerators.
So I think we had this conversation a few years ago actually and you blew my mind that I actually had no understanding of how a particle accelerator worked. And typically, I know a lot about the stuff that we talk about but this was one that you were like, “Here’s how they work,” and I was like, “What? No.” So can you kinda of get that part where I think it’s just amazing, just the core purpose of a particle accelerator, the whole mass energy, energy mass thing. So what are they?
Pamela Gay: So this is where I think everyone gets confused is they’re like, “How is it that we’re just matching together protons and we’re getting this really heavy thing out?” Well, what’s happening is you use a magnetic field in one form or another to take either one or two particles and get them accelerating so that they’re moving as fast as you can get them moving before relativity starts to get in the way. And it’s the combination of their kinetic energy and their mass coming together and all of it becoming pure energy during the collision that leads to the discovery of things like the top cork, like the Higgs Boson.
But the awesome thing is is that’s not the only type of particle accelerator out there. That’s just the sexy kind that we hear about in the news. There’s particle accelerators that are used to create ion beams, to burn out tumors in human bodies, to create neutron sources that we can use to make heavy radioactive materials. So there’s all sorts of different types of accelerators. There’s hundreds and hundreds of them on the planet Earth and the only one anyone ever knows about is CERN when it’s active, or Fermilab when it’s active and they seem to take turns.
Fraser Cain: But yeah. There are particle accelerators in hospitals and stuff.
Pamela Gay: Yes.
Fraser Cain: Yeah. So but I think I wanna go back because I think you didn’t quite get there. This concept that light, that energy and matter are interchangeable and that by dumping energy into these particles as you fire them around, you create heavy elements when the collisions happen. What’s going on there?
Pamela Gay: Yeah. So there’s two different things that you’re combining. First of all, the particle has E equals MC squared worth of energy. This is its rest energy. So you’re taking its mass. You’re multiplying it by the speed of light squared. So that’s a pretty good chunk of energy right there. Now, you’re then taking that exact same particle and multiplying its mass times one half because it’s kinetic energy times V squared in a non relativistic scenario and then that V squared gets even more complicated as you get closer and closer to the speed of light.
And all of that energy gets combined, essentially in some cases, almost doubling the mass of the particles that – not the mass. The energy of the particles that are colliding and that becomes vast and all of that energy is then in a very, very small point and it has the option to freeze back out as matter in a variety of different ways. And it usually cascades through multiple different particles at it settles back down to, well, whatever it’s going to be on the other side of the collision.
Fraser Cain: So you collide these particles together in these accelerators. They have all this energy in the mass and you always hear you could use a sugar cube’s worth of matter would act like a nuclear bomb if you could release all that energy. Right? But if you keep these –
Pamela Gay: Yeah, but we’re not creating sugar cubes luckily.
Fraser Cain: No. No, I understand that. No, no. But we’re taking individual protons and individual electrons and things like that but we’re smashing them together and you’ve got all that energy and then in that moment, you suddenly have, I guess, like a soup of an enormous amount of energy that can now freeze out into particles.
Pamela Gay: Yeah. And what’s awesome is the stuff that we hear about most in the news is when people are accelerating protons or electrons, typically towards targets. And when I say accelerating, what I mean is charge particles, when they’re exposed to a magnetic field, will move purposely through the magnetic field and if you have a nice cone of wires, that will generate a magnetic field through the center of that coil of wires and you can take and shoot charge particles down that coil of wires.
Now, a charge particle isn’t just an electron, it’s isn’t just a proton. You can actually take an atom, strip off its electrons and it becomes an ion. Now, you have a charge atom, basically. An ion that you can accelerate through this magnetic field. So now you have a significantly heavier mass object than just that one electron, that one proton that you’re accelerating through the collider. So now, you’re looking to get even higher energy experiments. It gets quite and awesome quite quickly.
Fraser Cain: Right. And I guess, so why do we need such – there’s the different kinds of particle accelerators and the different sizes of them. The one we hear a lot about is that it took a facility as big as The Large Hadron Collider to discover the Higgs Boson. So why was that so necessary?
Pamela Gay: Well, you’re looking at a couple of different factors when you’re building huge accelerators. First of all, is how easy is it to maintain the containment? So when you’re accelerating the particles, you typically are creating a big circular device. There are linear accelerators but the bulk of the ones that people are familiar with that are used in hospitals and in many research settings are circular ones. So you have a giant torus, a giant donut that you’re accelerating particles through and you have two factors. You have to keep the beam contained in the center of this donut that you’ve sucked all the air out of so that they’re not gonna accidentally hit a molecule of air.
So you need to consider how easy is it to suck all the air out of that. Luckily, vacuum isn’t as big a deal anymore. The second thing you need to consider is how do you keep that precise bend so that they don’t accidentally hit the sides of the container and how do you build the machinery to provide these acceleration? So now you’re wrapping that tube and very finely made magnets of different types.
And then you’re bending the beam. Now, anyone who’s driven a car knows that it’s easier to a nice, big, gradual turn than it is to do sharp little tiny turns and this is also true in cyclotrons. If you’re trying to keep a nice, constantly accelerating beam going, that nice big circle is gonna be much easier to keep things contained in, especially as you’re approaching the speed of light.
Fraser Cain: Right. And so because some of your energy is gonna be going to just keeping it going around that curve.
Pamela Gay: That’s why it’s called constant acceleration. Velocity is your motion in a given direction. The second you start changing something’s velocity, that takes energy. That requires that acceleration to be taking place. So you’re upping both the velocity of the particle instantaneous velocity. You’re increasing its speed constantly but you’re also constantly having to steer. So these nice, giant circles allow you to have that constant acceleration and to not have as hard a time building the giant machinery that you need and keeping everything tightly focused as you go faster and faster and faster and faster.
Fraser Cain: And do you know how many times these particles are going around these accelerators? Are they just doing one loop and then they’re smashing?
Pamela Gay: No. They’re doing many different loops. Exact number is gonna vary with how fast you need them to go, how focused you need the beam, how many particles you’re injecting into the beam. It’s not just once. It takes many times around to get all the way up to the kinetic energy that’s necessary for the explosions that they have at the end.
Fraser Cain: Yeah. It’s kind of amazing that they are able to, as you say, dump in almost to the point that has double the energy because that original E equals MX squared is such a vast number. You have to get more of that energy into it.
Pamela Gay: And you can ever start to get more than that except then you have to switch to using the relativistic equations because as you go faster and faster and faster, your momentum increases. Your effective mass increases as you’re going faster from relativistic terms and kinetic energy has relativistic terms so now you have that vast velocity and it seems like you have significantly more mass so now you’re exceeding but you need a new equation, that factor of two. It’s kind of awesome.
Fraser Cain: Yeah. Totally. Right. So then what are the different kinds of particle accelerators? You mentioned linear, the circular ones. So what different flavors do they take?
Pamela Gay: Well, you can look at the flavors both in terms of technology and in terms of what they do. So if you look in terms of what they do, you have medical cyclotrons that are used to blast out tumors. You have neutron beams that are used often to fire at heavier atoms at a very precise rate to build these heavier and heavier atoms. This is how we end up discovering heavier atoms periodically and they end up announcing that they’ve now found unobtainium. That one isn’t one they’ve actually found but you know what I mean.
Fraser Cain: I see. Yeah. So they’ve got some target atom and they’re firing a beam of neutrons at it hoping they stick and then when you’ve got a certain number that stick, then you’re like, “Did it. We got 108.”
Pamela Gay: Well, and more than just getting the neutrons to stick. You also need them to undergo beta decay so that some of those neutrons now become protons and now you have a heavier atom. So here, you’re replicating the conditions that you get inside of the atmosphere of stars, and in some process, in supernovae that allow the heavier atoms to get built. A lot of these heavier atoms are unstable. They collapse quickly so we don’t even get to study their properties unless we are able to build them in one of these accelerators with a neutron beam.
Fraser Cain: Right. Okay. And so you mentioned the different kinds of flavors. Right? So we’ve got the different kinds of experiments. You’ve got the neutron beams. You’re making antiparticles for cancer treatment. What else are they doing?
Pamela Gay: So then you also have some of the ion accelerators that are smashing together heavier mass atoms and recreating the conditions inside of supernovae. So we hear all about CERN recreating the big bang but then you have other laboratories like the national super conducting cyclotron laboratory, which is the longest named of the labs, I think. It’s up at Michigan State University and there, they’re smashing together ions and recreating the conditions and supernovae to see how is it that these different stellar nuclear synthesis events can take place.
Fraser Cain: And what is the difference between the linear and the circular ones? Is it just – size or?
Pamela Gay: Well, if you think about it, it’s size and also the potential energies involved. With the cyclotron, you can just keep ramping up the velocity by circling and circling and circling until you have the energy that you want and the particles. With the linear accelerator, you’re kinda stuck with that one track but linear accelerators were how we focused for a long time before people committed to building Fermi National Lab and the National Superconductor and Brookhaven has a cyclotron. Harvard had one for a while.
It started out that the really big accelerators were often linear accelerators and cyclotrons were your university sized facility but once you started getting to, well, Fermi National Lab here in the United States, they disbanded a town to put the facility in. So where there used to be a town, there’s now a large pair of circles that are filled with buffalo and literally, Fermi Lab has buffalo.
And then CERN’s even bigger and it spans both the Swiss and French country sides. So once you need to reach the sorts of energies that are achieved by these giant facilities, it’s hard enough to find area big enough to build the circle. Imagine trying to build something linear to do that level of acceleration. You’re just not gonna do it.
Fraser Cain: Do you remember the plans to build, what was it, the Superconducting Supercollider back in the ‘80s and ‘90s and it got cancelled?
Pamela Gay: Yeah. Down in Texas. Yeah. That was actually a very ugly situation, especially for the farmers involved because they went down, it was in Waxahachie, Texas and the government went down and used eminent domain to take away a lot of farmer’s fields and paid them an amount that their claimed was fair market value but none of the farmers could afford to buy land, replicate their farms and they ended having to find new careers.
Built this huge facility that had it been completed, would have revolutionized a lot of our understanding of particle physics but at the point where they dug the giant hole where they had all of the caves in place where instruments were starting to get built at a variety of universities around the United States.
There was a congressional blowback that this project had taken too long. Well, it turned out it was harder to build the holes than they’d thought. It turned out the equipment that they had to innovate from scratch wasn’t as easy to innovate as they’d imagined. So there was congressional blowback just like there’s been with the James Webb Space Telescope and so many other major facilities. And so congress decided to close down the facility. Partially built. Fill in the hole. Cancelled all of the instrument plans. Essentially fired all of the scientists.
And then, when they were done filling in the hole, they sold the land for a cost significantly higher than they’d bought it from the farmers. Sold it off to developers. So now, you have no science, no farming, and a bunch of developers making money. And so that was a tragedy at every single turn.
Fraser Cain: How would it have compared to CERN, The Large Hadron Collider?
Pamela Gay: It worked differently from the way they’re working CERN with The Large Hadron Collider. This was one that was going to be looking at moving heavier mass objects and so instead of doing the proton electron, the colliding of hadrons that you see at LHC and with the prior instruments they had there, instead it would have been looking, from what I remember on this one, looking at colliding, again, the ions.
Fraser Cain: Right. So then we’ve talked about how the structure and a bit about how they work. So what kinds of answers in science and especially, in our case, we’re interested in astronomy. But what kinds of questions can we answer with these particle accelerators?
Pamela Gay: Well, depending on which one that you’re looking at, it’s, “How do I cure cancer, how do I replicate the insides of a supernova, how do I replicate the big bang?” And my favorite is, “Is it possible to create a microscopic black hole in the laboratory?” And I think the replicating the events in a supernova is in some ways both the most mundane and the most interesting.
We often say in astronomy, we’re made of stardust. That’s probably the most common stated. It’s on jewelry. It’s on posters. It’s on inspiration this, that and the other thing but it’s a very easy thing to say, “We’re made of stardust,” but let’s prove it and prove it in detail.
And when we look at supernovae, we see the heavy atoms in the clouds of dust and material around them but exactly how do you go from a normal composition star to all of this heavy atoms? Well, it’s those intermediate steps that we’ve worked out on paper. Even graduate students are required to figure out many of these reactions but how do we replicate it and make sure that our theories are right, make sure that our detailed understanding of particle physics is right?
And the awesome thing is is for the most part, it is proving right but then there’s the open questions of well, “How did we end up in a universe that has more mass than anti matter? Where are the different asymmetries, the things that break down when we look at the details of particle physics?” Well, it’s when we make these collisions when we start creating the antimatter; we’re able to figure out, “Oh, so this is where this symmetry breaks down. This is where this symmetry breaks down.” And it helps expose, well, what’s under the hood of our universe.
Fraser Cain: Right. Well, so what would one of those experiments look like? If you’re trying to replicate a supernova without an actual supernova, what would that experiment look like?
Pamela Gay: So you have several different processes that you’re worried about with supernovae. With supernovae, one of the things that you get is a flood of neutrons that come pouring out and when that happens, those neutrons bombard the centers of atoms and as they build up, as they hit certain densities, you end up with a form of beta decay that ends up with some of the neutrons becoming protons and they release energy and neutrinos and all sorts of stuff in the process and you can quickly climb up through the atomic levels if you keep bombarding that system with neutrons so that as it jumps from one unstable place to another unstable place, you can eventually land somewhere stable.
There are amazing science maps that show this band of stabilities in the isotopes and as you go up the center, it’s a graph of number of protons, number of neutrons and so you start down at one, one, and then you just build your way up and you can follow this line of stability and in a really good one of these isotopic maps, it will show you what are called the rapid process and the slow process, the R process and S process element formation pads that just show the various decay rates and growth rates that occur through beta decay and inverse beta decay.
Fraser Cain: And so you can try to replicate those different conditions and see if things pop out in the way that you’re expecting
Pamela Gay: Exactly. Exactly. And it allows you to get an experimental hold on things like what is the half life of this or that, trying to understand how long something lasts for mathematics is not exactly – it’s just easier to build the thing sometimes.
Fraser Cain: So one of the things that we’ve been dealing with since we started Astronomy Cast was this idea of dark matter and it’s still kind of a bit of a mystery but I know particle accelerators have been brought into this search for dark matter.
Pamela Gay: And it’s gonna be interesting in the next few years is they try to push The Large Hadron Collider to higher and higher energies. There’s super symmetry theories. Theories that many, if not all of the particles we’ve discovered so far have a partner, super symmetric particle that’s their partner and these sister particles, some of them are projected to be what we now perceive or observe as dark matter, particles that don’t really interact via the electromagnetic force. They don’t stick together but do quite politely interact via gravity, creating micro lensing, creating acceleration of galaxies that are orbiting, of stars that are orbiting in galaxies.
So we have to find these particles with these strange sets of interactions. And neutrinos have a lot of these characteristics but they don’t exist in high enough numbers to be all of the projected dark matter that we’re seeing. So with particle accelerators, what they’re hoping is as they push to higher and higher energies, in that chaos of forming particles that comes out of that high density region of energy, some of the lowest mass dark matter particles, lowest mass super symmetry particles, they’re hoping they’re the exact same thing, will get formed and we’ll be able to go, “Aha! I got it,” in the laboratory.
They’re also using large – basically the same detectors they use for neutrinos to look for dark matter and it’s hoped that they’ll perhaps be able to find some of these as they look for the flickering interactions that indicate that one of these mysterious particles has had one of it’s extraordinarily rare interactions with one of the forms of heavy water or other fluids that they use in these neutrino detectors.
Fraser Cain: Right. So I guess you got the two ways. Right? The one option is you just have this big detector and just hope to find natural dark matter particles or you generate them in the particle accelerator and then try to see if you’re catching them. So we talked about dark matter. What about dark energy? Are there ways that we can use particle accelerators to find dark energy?
Pamela Gay: That one starts to get much more challenging. We’re still trying to figure this out. We’re still trying to understand what the heck is dark energy and part of getting at it is understanding better how it is that particles form, how they change. One of the experiments that’s getting done is there’s a lab in Italy that’s generating a neutrino beam that they’re shooting up towards one of the instrument at CERN and they’re looking to try and measure how do the flavors of neutrinos change over time. How do they go back and forth between mule and tao and electron flavors or of neutrinoness?
There’s similar experiments in North America. And as we try and understand more and more about these different types of interactions, theorists are working to try and understand how is it that – well, we know that energy’s constantly turning into virtual particles and those virtual particles are turning back again into energy and one of the thoughts for dark energy is maybe somewhere in this, there’s energy released that everything isn’t properly conserved.
And people are trying to understand all of these pieces through accelerators. They are also building telescopes where they’re trying to look at what’s happening in the earliest moments of the universe. It’s a completely different discussion. So we’re doing everything from trying harder to understand particle physics to trying harder to understand the formation of our universe. Where we’re gonna find the answer to dark energy, I don’t think there’s even a gambler willing to pick up that bet.
Fraser Cain: Right. I love this idea that you just take your neutron beam and you just aim it in the general direction of CERN and it goes right through the Earth and reaches the detector. You don’t need to build a tube or anything because the neutrinos just don’t even care.
Pamela Gay: And nuclear power plants. You can tell whether they’re on or offline by the neutrinos you’re receiving.
Fraser Cain: Right. So the last thing, I think, is really interesting. Well, there’s two that I wanna talk about. I’m running out of time but one, it’s creating these black holes, which you’ve mentioned briefly. Whoa. How does that work?
Pamela Gay: Yeah. Well, so what is a black hole? It’s a extraordinarily dense mass. It doesn’t matter that you have a lot of mass. What matters is the density of the mass. Can you stand on the surface of that mass and have to go greater than the speed of light to escape the gravitational pull of that mass? And so it’s theoretically possible to create microscopic sized black holes by just slamming things together with a beam that is tight enough and an energy density that’s high enough that, well, you meet those criteria for forming a black hole.
Now, if you’re able to do this, one of two things is gonna happen. That sucker is either going to just quite haphazardly sink down to the center of the gravitational well that is the planet Earth. It will oscillate for a while as it works to get there. Happily passing through the bulk of all of the atoms on the planet. It will maybe eat like – I ran the numbers a few years ago and it was just a negligible number of atoms such that a couple grams will be eaten before the sun starts to destroy our planet. So this is not a concern if this happens.
But the more interesting thing that could happen is it could evaporate. Its event horizon would be so small that it’s evaporating faster than it can consume energy from normal conditions. And if that microscopic black hole is able to evaporate in the flash of light that’s predicted, then Steven Hawking finally gets his Nobel Prize, which I think would make a lot of people happy.
Fraser Cain: And so the last thing before we go is replicating the conditions of the big bang, which is crazy.
Pamela Gay: Yeah. So if you think about it, what was the condition of the big bang? It was dense. And so all that it takes to create the – all that it takes to start to replicate the conditions of the big bang, you have to take energy and compact it into the densities that were experienced at different points after our universe had started to expand out. And supernovae are pretty dense but the early universe was even more dense and that just requires higher energies and tighter focus.
Fraser Cain: So you’re just smashing the particles and they’re piling up in a pile in the middle of the accelerator, I guess, the experiment.
Pamela Gay: No pile. They’re turning into energy in the center of the experiment.
Fraser Cain: In the center and the density of that area gets higher and higher and higher until you’re starting to replicate. And I know I was doing a little research on this that in the LHC, they got into the trillions of degrees for one of their experiments.
Pamela Gay: And what I love is as you start talking about particle physics, when they discuss the massive things, they stop using normal units and start discussing the amount of energy that’s contained in something instead. Because when you’re dealing with relativity all the time, it’s just easier to work in units of energy. So here, normal energies are in the giga electron volts and you just work your way up from there. Tera electron volts is now not too uncommon for these giant research colliders.
Fraser Cain: What will be next? Peta –
Pamela Gay: Peta.
Fraser Cain: Electron volts? Yeah. Yeah. That’s crazy. Cool. Well, thank you very much, Pamela. That was awesome. It’s great to have you back.
Pamela Gay: It’s good to have you back as well. We both took turns not being here this time.
Fraser Cain: Totally. Alright. We’ll see you later.
Pamela Gay: Okay. See you later.
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Duration: 34 minutes

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