# A question about energetic protons (cosmic rays)

1. Mar 7, 2009

### fluidistic

I've read that some protons in the Universe can have an energy of about $$10^{20}eV$$, or in English, about a well-hit tennis ball. (The cosmic rays).
Is it possible for these rays to reach our brain? Or more precisely, what would happen if one gets hit by such an energetic particle?
P.S.: I didn't know in which section to post this question. Sorry if I did it wrongly.

2. Mar 8, 2009

### Chronos

Cosmic ray collisions occur every day with everyone . . . no news there. They are too few to have quantifiable physiological consequencesg

3. Mar 8, 2009

### Chalnoth

These high energy rays don't actually get very far through the atmosphere. They tend to impact and obliterate the nucleus of some atom in the upper atmosphere. What hits the ground is a massive shower of particles (it's by measuring these showers that we are able to detect these particles and measure their energies).

The products of these collisions that have the most effect upon matter on the ground are muons. Muons are like electrons but with around 200 times the mass or so (meaning they're around 1/10th the mass of a proton). When they strike normal matter, then, they can knock out electrons, and when they decay, those decays can cause more electrons to be knocked away from their atoms. These cosmic ray muons are a significant source of random mutation that we have to deal with all the time and can cause things like cancer. They're not really anything to be worried about, per se, because they're ever-present and we normally don't notice their effects. And we can't realistically do anything about them anyway.

And this is also why, by the way, we don't worry quite so much about small amounts of radiation exposure: we're exposed to radiation all our lives, after all, and so it's not really that big of a deal unless this exposure is increased significantly more than the background level.

4. Mar 8, 2009

### marcus

Fluidistic, I've read the same. Some cosmic ray protons have energies on the order of 10 joules. That is a lot. Like dropping a 1 kilogram book one meter, kerblam onto the table top.

These energetic particles spend their energy in the atmosphere. They cause showers of secondary and tertiary particles.

I hope you get a thorough answer, about the effects on the body. It's interesting. It is mainly interesting because of constraints on manned space missions. People have to be shielded from the radiation in space.

I can't give you a very satisfactory answer. Maybe you can find something in Wikipedia. One unintuitive thing is that the momentum of one of these protons is not so big.
The kinetic energy might be like a dropped book or a hit tennisball.
but the momentum wouldn't be like those things.

I'm heading off to bed. I'll check in tomorrow and see if someone (you or other) has found out more about the effects on the body.
You should probably expand the question and include the effect of less energetic more common cosmic rays. I assume those with a joule or more energy are comparatively rare.

5. Mar 8, 2009

### Chalnoth

Huh? As these are highly relativistic particles (kinetic energy much greater than their rest mass energy), their momentum and energy are essentially equal (up to a unit conversion factor given by the speed of light).

6. Mar 8, 2009

### fluidistic

Thanks all, that was very interesting. I also read on wikipedia that the cosmic ray can damage computers.

7. Mar 11, 2009

### v2kkim

Possibly is it safer living low altitude regions ?

8. Mar 11, 2009

### Chalnoth

I don't think it makes any meaningful difference. The muons generated by these cosmic rays tend to be very penetrating. Certainly there's no meaningful difference in the range where people usually live.

9. Mar 13, 2009

### v2kkim

Can muons penetrate even concrete ? How come so penetrating ?

10. Mar 13, 2009

### Chalnoth

Oh, certainly. They go quite far through basically any sort of matter. This is why neutrino detectors have to be put so far underground: if they aren't buried under hundreds of meters of rock, the muon signal completely swamps any neutrino signal.

The reason they are so penetrating is basically that they tend to be in sort of an in-between regime in energy where they don't react strongly with atomic nuclei, and they also have enough mass that it takes a long time for interactions with electrons to slow them down much (muons are about 200 times as massive as electrons, but only about 1/10th the mass of protons/neutrons).

11. Mar 13, 2009

### v2kkim

I think some medical suppliments are advertised to repair radical damage in our body. Maybe I have to take good ones.

12. Mar 14, 2009

### Chalnoth

I would stay away from those if I were you. The food supplement industry in the US is almost completely unregulated, and so there's a bunch of dangerous **** out there, and there's almost no demonstration of any positive effect whatsoever.

Besides, this really is nothing to be concerned about. Animals on Earth have lived with this continual low-level bombardment of cosmic radiation for hundreds of millions of years. We've evolved to compensate, and there may even be negative effects from shielding ourselves from it.