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Old Mar 27th 2018, 01:35 PM   #1
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Question Radioactive source problem

Hello!
I have a question about nuclear physics.

Let's assume that we have an a-particle radioactive source with very high activity, let's say 100kCi (hypothetical scenario).

If we leave this source in our office for example we are completely sure that we are safe from radioactivity: that is because the range of the alpha particles in the air is very small (in the order of cm I think).

Let us now cover the source with a material with low Z (atomic number), let's say up to Aluminium (Z=13). The question is: are we now more in danger? And why?

My intuition says that yes we are more in danger. But I'm not sure why. Is it because the alpha particles ionize the particles of the material that we covered the source? Is it something else?

Any ideas?
Thank you!
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Old Mar 27th 2018, 10:33 PM   #2
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The question here is what happens to an alpha particle when it's absorbed by the aluminium ...

It converts it to phosphorus and one neutron . the neutron is emitted as radiation.

High level Neutron radiation is damaging to humans ,

But the amount of neutrons we are dealing with here is not going to cause any harm, anyway the alpha particles will react with something ...with nitrogen in the air it is absorbed to create oxygen and emits a proton , which is probably worse than a neutron ....

I doubt you need to be concerned about this , if you are just put the source away from people ...
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Old Mar 28th 2018, 07:05 AM   #3
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Originally Posted by kvothe View Post
Hello!
I have a question about nuclear physics.

Let's assume that we have an a-particle radioactive source with very high activity, let's say 100kCi (hypothetical scenario).

If we leave this source in our office for example we are completely sure that we are safe from radioactivity: that is because the range of the alpha particles in the air is very small (in the order of cm I think).

Let us now cover the source with a material with low Z (atomic number), let's say up to Aluminium (Z=13). The question is: are we now more in danger? And why?

My intuition says that yes we are more in danger. But I'm not sure why. Is it because the alpha particles ionize the particles of the material that we covered the source? Is it something else?

Any ideas?
Thank you!
I agree with oz's answer. Just don't eat it. (They always stress that point in the radioactive safety manual. I don't think it needs to be mentioned... If anyone has deliberately eaten the stuff then I think they're in line for a Darwin Award.)

-Dan
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Old Mar 28th 2018, 11:20 AM   #4
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The question was asked by our professor during a lab class about aplha particles, it's a theoritical question.

We don't cover the source with aluminium only, we cover the source with a low Z material (up to Z=13 for example).

So the answer has to do something with materials with low Z (low Z means low densities?), not particularly aluminium. Maybe the alpha particles cause other (nuclear?) interactions, so it becomes more dangerous?

Anyway, if you have any ideas feel free to post them, thank you for your answers!!
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Old Mar 29th 2018, 02:11 AM   #5
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You would have to find out what the cross-section is for the particular alpha-capture reaction. Then you can find out a nuclear reaction rate. At terrestrial temperatures, the alpha-capture rate is going to be small, but non-negligible.

Presumably the question is targeted at whether the products of an alpha-capture are dangerous, so we need to investigate the products of nuclear reactions on a case-by-case basis.

Most aluminium is in the form of stable $\displaystyle ^{27}$Al, so we have $\displaystyle ^{27}$Al($\displaystyle \alpha, \gamma$)$\displaystyle ^{31}$P, $\displaystyle ^{31}$P is stable, so it's safe. It's probably going to be the dominant reaction as well.

We also have $\displaystyle ^{27}$Al($\displaystyle \alpha, n$)$\displaystyle ^{30}$P. $\displaystyle ^{30}$P is unstable ($\displaystyle \beta^+$ decay) with a half-life of 2.5 minutes, so that could be dangerous if you're close to it.

A sample of aluminium will have a small amount of $\displaystyle ^{26}$Al, so there's also the possibility of $\displaystyle ^{26}$Al($\displaystyle \alpha, \gamma$)$\displaystyle ^{30}$P, so it seems that there's a chance that you're going to get some radioactive $\displaystyle ^{30}$P.

EDIT: The gamma rays and neutrons from the reactions might be harmful too, but I'm not sure without looking into the energetics of it, which could take a while!

Last edited by benit13; Mar 29th 2018 at 02:48 AM.
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