# Ionizing Radiation in a Cloud Chamber

1. Mar 23, 2013

### rkum99

Hello!

I've been doing a lot of research on cloud chambers recently, and I've
come up with a quite a few questions on the behavior of certain types

1) For a start, I assume that gamma-rays and X-rays will induce Compton
scattering inside the cloud chamber. Would a photon realistically undergo
the compton effect multiple times?

My guess: Yes. However, after a few times, the photon will no longer possess
enough energy to undergo the compton effect.

2) I know the compton scattering equation:

λ' - λ = (h/mc) (1 - cosθ)

Unfortunately, I can only realistically approximate the value for λ, while I have
no way to find the value of θ or λ' based on the trails in the cloud chamber. Is
there any way I could figure out or at least estimate such values?

3) The trails caused by beta decay in the cloud chamber bend much less than electrons
created through compton scattering by gamma rays. Is there any scientific reason
for this phenomena?

I'm assuming that my "compton scattering assumption" is accurate. If it isn't I would
appreciate if a better explanation could be provided.

I'm not sure if this should have gone in the homework section. If it should

Thanks for the help!

2. Mar 24, 2013

### Staff: Mentor

If the energy is high enough, sure. Pair production is possible, too, if the energy is high enough.

Ýou will need the electron energy, the direction of the photon source or the direction of the photon afterwards, I think.

Less energy for Compton photons. That depends on the energies of your photons and beta decays.

3. Mar 24, 2013

### rkum99

Hello!

2) So it is unlikely that I will be able to mathematically analyze
what happens in a cloud chamber, since I cannot measure
the angle with which an electron shoots out in a cloud chamber.

3) Is it valid to say that when a free electron interacts with an
atom, the coulumbic forces between the two particles could
knock out an electron and bend the incoming electron (provided
it as enough energy)?

Note: THe gamma source I am analyzing is uranium ore. I am
comparing the electron trails from compton scattering to
the beta trails emitted by the uranium ore.

Thanks for the help!

Last edited: Mar 24, 2013
4. Mar 24, 2013

### Staff: Mentor

Anything would work, including the energy of the electron (curvature in a magnetic field?).
That is a possible process, indeed.

5. Mar 24, 2013

### rkum99

Hello!

So higher energy beta particles, that have more kinetic energy
and momentum are able to retain their original path better than
lower energy particles, which can be more easily bent by a force.

So why do some high energy beta particles not ionize at all. Would
it be due to a smaller timeframe between which the coulombic forces
between the two electrons interact?

6. Mar 24, 2013

### Staff: Mentor

Which particles do you mean?

The ionization rate drops with increasing velocity (and slowly rises again for very high energy), but it does not go to zero.

7. Mar 24, 2013

### rkum99

Hello!

Oh, that seems to make more intuitive sense.

In the cloud chamber, high energy beta particles didn't
create any trails, so I assumed that they were not
ionizing the vapor.

I suppose it simply didn't ionize enough particles to create
noticable trails. Another question that pops up:

Why would the electrons have a somewhat low energy? Is
there a scientific explanation for this phenomena?

Last edited: Mar 24, 2013
8. Mar 24, 2013

### Staff: Mentor

How did you know they were there?
Which electrons?
Compton electrons have a broad distribution of energy, as you can calculate with the help of the formula in the first post.

9. Mar 24, 2013

### rkum99

Hello!

That is a good point......:rofl:

The beta source was certainly radioactive though -
the geiger counter registered a large amount of radiation
from it. I have heard of cases where a substance is so
radioactive, the cloud chamber ceases to work well (I have
no idea why).

Sorry for the vague questions, but the electrons I was
talking about were those that were compton scattered in
the cloud chamber. It my cloud chamber, the electrons
that were scattered tended to bend easily, so I assumed
they had lower energy than beta particles (which did not
bend easily).

I was wondering if there was any reason that the electrons
tended to have lower energies. Lots of the electrons were
bending, so it didn't seem like it was completely randomized
(although it seems like it should be).