Ep. 515: Space Radiation

Posted on Jan 25, 2019 in Forces, High Energy Physics, Missions, Physics, podcast | 0 comments


Space is a hostile environment in so many ways. But one of its worst features is the various kinds of radiation you can find. When astronauts go back beyond the protective environment of the Earth’s magnetosphere, what are the various kinds of radiation they’ll encounter. And is there anything we’ll be able to do about it?

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Show Notes

Radiation – what is it?

Three kinds of ionizing radiationAlpha particles, Beta particles, and Gamma particles (and X rays)

Cosmic Rays  come from stars, supernovae and active galactic nuclei – and can’t be avoided in space travel

Earth is protected by our magnetic field (Van Allen Belts) generated by our active volcanic core

What does traveling through the Van Allen Belts mean for spaceflight?

Coronal mass ejections and solar winds

Ideas for Radiation Shielding

Transcript

Fraser Cain: Astronomy Cast, Episode 515: Space Radiation. 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.

I’m Fraser Cain, publisher of “Universe Today,” with me as always, Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of Cosmo Quest. Hey Pamela, How ya doin’?

Dr. Pamela Gay: I’m doing well, how are you doing, Fraser?

Fraser: Good, we just got the news the shutdown is over. Hopefully, people are gonna to be getting their paychecks, the science is going to be rolling out. The rovers, the telescopes are still gathering data. We just didn’t know what happened. So, now were going to find out. So, I think everyone –

Dr. Gay: Well –

Fraser: – should just buckle up for a news storm of space news.

Dr. Gay: I hope you’re right. I suspect that it’s gonna be more of a slow roll as everyone panics for three weeks to find out if the –

Fraser: If it’s coming back. Right.

Dr. Gay: – shutdown, yeah.

Fraser: But, as a person who has troll through – troll – troll – troll. Anyway, I as I have to look through all the news every day. I would say a third of the news that we get comes from NASA, directly. Pictures from the space station, information from the missions, press releases from the projects they’re working on and it’s been rough, to not have access to these sources of news. So, I’m so glad everyone at NASA is going to be back, and I can’t wait to get all the science.

Dr. Gay: Well, don’t count your votes until they’re cast. There’s agreement that there will be an agreement, but they haven’t voted yet. I’m gonna hold my breath, not literally.

Fraser: Sure, yeah. I may have to take this all back next week when the vote didn’t go through and shut down continues, but I hope not. I hope we will get to see tons – I’ve missed all these missions.

Dr. Gay: Yeah.

Fraser: What happened with OSIRUS-Rex, it’s at an asteroid right now. What’s happening with Parker Solar Probe – anyway –

Dr. Gay: That was a long sidetrack at the beginning of this episode.

Fraser: Yeah.

Dr. Gay: Hello, we love you all. We’re actually here to discuss space radiation.

Fraser: All right, let’s do it. Space is a hostile environment in so many ways, but one of its worst features is the various kinds of radiation that you can find. When astronauts go back beyond the protective environment of the earth’s magnetosphere, what are the various kinds of radiation they’ll encounter, and is there anything we can do about it?

Space sucks. We’ve mentioned this before, mention this again. It’s the worst; the entire universe is trying to kill you, and the radiation –

Dr. Gay: Every day.

Fraser: Every day, and the radiation is one, just one example of the ways that the universe has it in for you. What kind radiation is out there?

Dr. Gay: Well, in general, we are looking at three different kinds of radiation, and were going to go through them in Greek alphabet order. Because, one of the things that that happened, in science, is they discovered the radiation forms before they figured out what they were. So, they gave them these awesome names, alpha particles, beta particles, gamma particles. Then, we figure out what they are, and far less interesting it turns out. So, alpha radiation is the lamest of all forms of radiation. It can’t even penetrate your skin. So, as long as you don’t eat it, inhale it you’re okay.

Fraser: Right.

Dr. Gay: The problem is you can eat it and inhale it. So, this is the kind of radiation that that you get from like radium, radon, uranium, thorium just regular every day nuclear breakdowns and – yeah, it’s lame, but it will still harm you, cause death, destruction if you’re exposed for too long. Now, going back to the – we named it before we knew what it was – and when we figured out what it was, it was lame.

It turns out alpha particles are just ionized helium atoms, and so since helium doesn’t generally pass through your skin, your good until you inhale it. Now, not all helium is alpha radiation. Otherwise, inhaling balloons would be a deadly thing to do.

Fraser: Right.

Dr. Gay: So, here were looking at specific forms of high-energy helium that is ejected, bereft of electrons, when nuclear breakdowns occur.

Fraser: Okay, those are alpha particles.

Dr. Gay: Those are alpha particles.

Fraser: But, I mean we don’t just find those in space. You’re laying the ground work here for the different kinds of radiation that you’ve experienced…

Dr. Gay: Yeah.

Fraser: – and then, we’ll talk about where we find it in space.

Dr. Gay: Exactly, and you do find these in space.

Fraser: Yeah, we’ll get to that in a second.

Dr. Gay: Yeah. So then, we have beta radiation. So, alpha, beta, we’re lame. These are, again, particles. Here were starting to look more at electrons. So here, you have a high-energy electron sent your way and here – they can penetrate your skin, but they don’t get too far in. If you’re exposed to beta radiation for too long, it will harm your skin.

It’s not gonna kill you quickly, and for this we are glad. Because, beta particles come from things like carbon-14, which is everywhere we use it for carbon dating. So, beta particles, kinda lame; high-energy electrons they happened, they’re everywhere. We also get them from things like tritium, sulfur-35. All these regular every day, radioactive particles breakdown, throw off beta radiation. So, alpha, beta.

Fraser: Okay. I think you’re saving the worst for last, aren’t you.

Dr. Gay: Yeah, I am. So, far we’ve gone particle, particle, and now we’re kinda looking at gamma radiation, and also x-rays. They forgot about x-rays when the first name things, so they kinda get lumped together. This is photons, which are both a wave and particle, and so is everything else, but have no mass so they fall into their own thing. We call them light. Gamma rays and x-rays, these start to pack the kinds of energies that will blast apart your molecules. This is bad.

Fraser: Unless you’re the Hulk.

Dr. Gay: Or Spider-Man, I guess.

Fraser: Yeah.

Dr. Gay: Spider-Man did pretty good.

Fraser: Well, wait a minute. He was bitten by a radioactive spider, and so the [inaudible] [00:07:21].

Dr. Gay: … and he got super powers.

Fraser: Right, but I’m guessing it was more of an alpha or beta particle you think about it, right? While the Hulk –

Dr. Gay: That would make sense.

Fraser: – got hit by gamma radiation, and those what the Fantastic Four got hit by. The point is, don’t count on any of these kinds of radiation to give you valuable superpowers.

Dr. Gay: No, they might give you un-valuable deadly mutations. So avoid? Avoid.

Fraser: Right, but the gamma radiation – this is electromagnetic radiation that’s caused by stars, by supernovae, by nuclear reactors and they are just like light, but just way at one end of the electromagnetic –

Dr. Gay: Yeah.

Fraser: – spectrum, and bust up your DNA.

Dr. Gay: And, there are all sorts of different ways to produce both gamma rays and x-rays. If we required radioactive substances to produce x-rays. It would be a whole lot more dangerous to go to the dentist. So, it’s just light. They just have to produce high-energy light instead of like hue, Phillips bulb light. Those are the primary kinds of light that were easy to detect in the 1800s, which is when most of these things were first identified. Nowadays, we know that it’s not just the alpha particles, which is helium.

It’s not just the beta particles, which are generally electrons, is not just the gamma rays and x-rays which are light. There are also these nasty critters called cosmic rays. Cosmic rays are where you start to impact energy en masse. So, here were starting to look at bigger nuclei. We are starting to look at things that can be 100,000 times more powerful than gamma rays; and gamma rays will kill you.

Fraser: Right, all right. So, let’s go back around to the beginning, now. Essentially, you can have protons, you can have electrons, you can have particle – photons – and you can have like blobs of various –

Dr. Gay: Nuclei.

Fraser: – particles mashed together. Those are the flavors that you encounter. So, when you go to space, when do you encounter these different kinds of radiation? So, what’s the –

Dr. Gay: The most common things are going to encounter in space are those nasty cosmic rays. They are coming at you from a combination of the sun, from distant supernova, from the accelerators that we call accretion discs in the center of distant galaxies. All of these different high-power magnetic field systems are accelerating atomic nuclei, just like Stern and Fermi, except towards us. If you’re not careful, you’re gonna catch the wrong kind of cosmic ray.

Fraser: These cosmic rays are relentless. It is like a fog when you get outside of the Earth’s protective magnetosphere, it is like this fog that is constantly going on. That you are just receiving – your bathing in these high-energy cosmic rays, and there’s no place to run, and there’s no place to hide unless you hide.

Dr. Gay: Fair, fair.

Fraser: Unless you put some protons in between you and the cosmic radiation, but the point is that while you’re out in space walking around the surface of the moon, you’re going to be getting a constant, relentless dose of this radiation. What are the effects to astronauts?

Dr. Gay: Well, so far we haven’t generally sent astronauts, except for Apollo astronauts, beyond the Earth’s magnetic sphere. This is where we are actually kinda lucky to live on a planet with active volcanism and tons of earthquakes. Because, that internal dynamo that is driving plate tectonics is also driving a magnetic field that, admittedly is on the run, and currently escaping across Siberia.

Fraser: Yeah.

Dr. Gay: But, is still generating a powerful enough magnetic field that particles that are coming at the earth are, in general either in the magnetic fields – creating our Van Allen Radiation belts, or they hit our upper atmosphere, which also serves to protect us. Because, collisions between these cosmic rays and particles in the atmosphere ended up breaking the cosmic rays and generating a cascade of lower energy particles.

This is Cherenkov radiation that we can detect here at the surface of the planet. So, between this combination of a planetary magnetic field, and an atmosphere; a lot, not all but a lot of the cosmic rays get broken down into harmless bits and pieces.

Fraser: So, it’s interesting NASA’s Curiosity Rover, when it flew to Mars, it did the long multi-month journey, and carried an instrument on board called the Radiation Assessment Detector –

Dr. Gay: Yeah.

Fraser: –RAD, and it was essentially trying to figure out what kind of exposure astronauts would get over a mission like that. So, that if you know that you can be sending astronauts to Mars in the future, just see what happened to Curiosity, and then do the math. So, the problem is they got a lot the Curiosity Rover got a lot of radiation, and it’s all it’s almost entirely from this this cosmic this galactic cosmic radiation that you are mentioning. This nonstop fog that’s just out there all the time doing damage.

I’m trying to find the exact number but it was it was something like – essentially, it’s just an enormous increase risk of developing cancer over the lifetime of an astronaut. You do a mission to Mars, spend some time, jumping around the surface of Mars. Looking for Mars bugs, and then you come home, you will experience a dramatically increased exposure of radiation, over that that time.
And there’s really no way that we know to avoid that.

I’m surprised you went in this order. Because, that’s like the worst one, and you also mentioned the other forms, which is the trapped radiation that we see around planets, and then there’s one other I wanted to get into. So, let’s talk about the trapped radiation, the Van Allen belts, et cetera.

Dr. Gay: Right, so the Van Allen belt is essentially a set of – and it is actually two different belts – that go around the earth at different altitudes. There are temporary additional belts that can form and dissipate. These are places where the Earth’s magnetic field is like, “And, I shall keep you,” to high-energy particles. So, high-energy particles that would otherwise be happily making their way through the solar system, perhaps careening into our planet’s atmosphere, careening into our planet, careening into us.

Instead, they get bent by the magnetic field, just like iron filings do when you play with the iron filings and magnet; and where iron filings will lock into the shape of the magnetic field. These charged particles that already have the trajectory, are simply going to get bent into following those field lines and orbiting around our world. Caught up, and here orbiting isn’t quite the right word I should be using. It’s orbiting in the sense of something going in a circle caught up in this magnetic field.

Now, the lower of the two Van Allen belts is actually higher than low Earth orbit. The Apollo astronauts when they went to the moon. They actually steered around the lower Van Allen belt going above it, and they very briefly passed through the upper belt. We do everything we can to try and prevent people and spacecraft from going through these belts and enduring long periods of time there.

We’ve actually gotten into the habit, which is a good habit to have of just kind of shutting things down when they pass through the belts in hopes that any additional charge dumped into the system through an interaction with this charge and the belts won’t melt our circuitry

Fraser: All the Apollo astronauts were wearing a dosimeter –

Dr. Gay: Yeah, dosimeters.

Fraser: – yeah on their spaces while they were doing their pass through the Van Allen belt, and I think NASA had set some amount of rads, or millisieverts that they were able to receive during that mission. Actually after they did the mission, they only ended up with about 1 percent of the radiation load that NASA was concerned about. So, in fact, as you said, avoiding the lower Van Allen belts, moving quickly up and over the higher Van Allen belts really minimize the risk. That’s for the earth, but if you go to Jupiter it so much worse.

Dr. Gay: Don’t. Yeah, so the radiation levels that are allowed are actually set in the United States by the Occupational Safety and Health Administration, otherwise known as OSHA. They’re federal guidelines, and NASA has been able to get a variety of waivers allowing astronauts to receive higher dosages than your average employee working at like the pharmacy down the street is allowed to receive.

The Apollo astronauts, as you said though, did receive far less then that OSHA limit they were worried about hitting up against the high end of. Now, this was in part due to luck. The sun behaved quite nicely while the astronauts were up on or around the moon, and out away from the protection of our magnetic sphere.

So, yeah we got really, really lucky with the Apollo astronauts in this. This isn’t the kind of thing we want to rely on and we don’t want to only send people to Mars during like solar minima or things like that.

Fraser: Right, but that’s a whole other issue is we’ve got the trapped radiation that is around the Earth, the Van Allen belts, you have to navigate, go quickly. Don’t rely your electronics, while you doing this, you got the galactic cosmic radiation that is this constant stream, and then the wildcard as you mentioned, is the sun –

Dr. Gay: Yeah.

Fraser: – which can be completely safe, or deliver a lethal blow to astronauts in a matter of hours, depending on the level of activity on the sun. How bad can that get?

Dr. Gay: Well, it can get bad enough to destroy spacecraft. We’ve had coronal mass ejections that have – as the charged particles that are part of the coronal mass ejection pass through spacecraft, they will earn out sensors, they will add their charge to the internal systems doing the moral equivalent of blowing fuses. Then, they’ll also shake the Earth’s magnetic field.

So, when you move the magnetic field. This then generates electricity in nearby objects and when that electricity is generated in the Earth’s power grid, as has happened in the past. This will also blow out the Earth’s power grid. So, here on Earth we can have our spacecraft destroyed and our power grid shorted, and this is happened in the days before we had the low power, highly sensitive electronic systems we have today.

If any of you ever tinkered with a radio or television set back in the 60s or 70s, you remember being able to like manhandle the wires with tweezers and pliers, and check things with your sensors with your little box, you picked up at RadioShack. You could play with the system. You had to make sure you didn’t accidentally hurt yourself with the capacitor, and in general you were going to destroy anything. Today, our electronics are much smaller, they’re much more fragile. I certainly wouldn’t be using any of my pliers that I’ve had since undergraduate to fix anything I like today. Because, these are two big for any electronics I probably still own.

With this reduction in size, with the reduction in required electricity. We also have circuits that are much more sensitive to that one straight cosmic ray hitting the wrong piece of silicone and breaking through that molecule thick, thin film and destroying your whatever it is that you love.

Fraser: So, let’s talk about prevention, safety. What can you do if you’re – the plan right – the Orion capsule is under development, right now. The space launch system is in development. They’ll probably fly – if not them there, of course, is all of the work that SpaceX is going to be doing. Sending hundreds and hundreds people to colonize Mars. What can you do to protect yourself against that radiation in space?

Dr. Gay: The canonical thing that they’ve done is thick aluminum shells. By thick I mean 3 millimeters. This is enough to start to break a lot of stuff, but it’s really not can help you enough against those cosmic rays. Alpha particles, cool. Beta particles, cool. Gamma rays, they’d rather you have a lot thicker of a layer, but this is a start. Unfortunately, what you really need is a layer of soil or a layer of water surrounding you.

Fraser: Like, a lot of protons.

Dr. Gay: Yeah.

Fraser: Right. Of those three things we talked about, of the trapped radiation, and the material coming from the sun, those are relatively easy to block. They’re not moving with a lot of speed – your aluminum et cetera, but it’s the cosmic rays. The chunks of supernova that are coming your way, those will just go right through all kinds material.

Dr. Gay: Well, and so will the gamma rays and x-rays.

Fraser: Yes, yes.

Dr. Gay: So basically, the more likely it is to kill you, the harder it is to stop and this is where we start getting to weight issues as well. Human beings, we’re giant bags of water. We’re giant bags of water that need food, we need air, we need water. The question becomes how do we protect ourselves, and any other life we might be taking with us from all of that radiation, without making our spacecraft way so much that it becomes intractable for us to get there.

Various pie-in-the-sky ideas that have deeply amused me, but I don’t think would work, include things like – well, have your water stored in the outer hull of the spacecraft. Fill it with tilapia while you’re at it. I don’t think that would work. That would have a really bad moment of inertia.

Fraser: Water is heavy.

Dr. Gay: Water’s heavy, and it would have a really bad moment of inertia. There have been people have talked about – well, let’s just generate a magnetic field. That requires a ton of electricity.

Fraser: Yeah, yeah. I think, just to go into that for one second, I’ve been following this space very carefully about –

Dr. Gay: Yeah.

Fraser: – well, just generate a magnetic field. I’m sure a ton of the listeners that are listening right now are like, why don’t they just make an artificial magnetic field. We know how to run electricity through wire, and make a magnet. People have been struggling with this idea literally for 50 years, and even with superconductors with incredibly powerful power sources that we have available right now; they still can’t make the power and strength of the magnetic field that you would need be compared to just dirt or water.

Still dirt, water, aluminum is a much better plan than attempting to generate an artificial magnetic field. Now, it could happen in the future, but for now, we don’t have any way to be able to do it, and this idea – NASA has paid multiple times for studies to try to solve this. There was the folks at CERN had recently done some research on this as well. Attempting to generate a superconductor magnetic field, and will be great. Where you flick a switch, boom on come the shields just like Star Trek.

Unfortunately, we just – so far, that technology has eluded everybody who’s attempted to do it. But, there are still people out there. There are probably a dozen people still trying to work on this technology.

Dr. Gay: One of the great frustrations with magnetic fields is they also, like so many other things in science, follow what’s called the 1/r2 rule. This means as you get further from the center, the field strength goes down as the square of the distance. So, you triple your distance, you have nine times less magnetic field. Now, the inverse of that is the closer you get to the center the worse the magnetic field.

I remember when I worked at Harvard at one point we were moving the gignormous magnet that was from an NMR machine, and I was warned, “Do not stick your head inside the magnet. Your brain won’t appreciate it.”

Fraser: Right.

Dr. Gay: I’m not sure I want to have to live inside of a small magnetic field with the 1/r2 law, which means I am always experiencing more magnetic field than I might appreciate.

Fraser: Right, so other idea, of course – the future colonists that are all on their way to Mars; or the moon – is just live underground. As you said, get some dirt between you and space. Do you remember Seveneves?

Dr. Gay: Yes.

Fraser: At the end of the book, a bunch people settled in a crack deep down, but still exposed to space; but just by reducing the amount of – being at the bottom of a chasm, you just minimize the amount of – the total amount of space that’s shining down on you to just the stuff that’s can be directly overhead, and really dramatically minimize the amount of radiation that you’re going to receive.

So, you don’t have to necessarily live underground, but you definitely don’t want a lot of sky.

Dr. Gay: This is where what you start imagining is the high-tech version of the Mesa Verde people. Here in United States out in the Colorado four corners area, there were peoples that were cliff dwellers. They built into the sides of these amazing canyons, vast cities; and they just existed in the cliff caves and had amazing architecture. Someday, we may be replicating what they did. Except instead of being the Anasazi, it’s gonna be us, and I’m cool with that.

Fraser: Right.

Dr. Gay: Let’s become the Mole men of Mars. The cliff ladies of the moon, and see what we can find to live with down deep in the craters.

Fraser: All right, well you send me a postcard. I will enjoy living here on Earth right live outside, and see oceans, and trees and stuff.

Dr. Gay: Okay.

Fraser: But, all right. Well, thanks Pamela. We’ll see you next week.

Dr. Gay: My pleasure, talk to ya later.

Announcer: Thank you for listening to Astronomy Cast, A non-profit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 1900 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Searle, and the show was edited by Susie Murph.

[End of Audio]

Duration: 30 minutes

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