# Penetration of beta particles

1. Jan 6, 2008

### prochatz

If we want to secure an area from beta particles, we could use absorbers, for example aluminum foils. Is it preferable to use one thick aluminum foil or several aluminum foils (with same total density as the first one of course) with free space between them? In other words, does a beta particle lose energy differently while passing through a thick foil in comparison with a beta particle passing through several foils.

2. Jan 6, 2008

### malawi_glenn

it depends how tight you have the Al-foils and what beta-energy you have. Remember that beta particles are stopped in pure air too. But the range in air is of course much larger than for Al, so if you want to shield effectivly, I would use a thick Al- foil

Do you understand?

3. Jan 6, 2008

### pam

Only the total thickness of Al matters.

4. Jan 6, 2008

### malawi_glenn

but does not air play a role?

10cm-Al that is positioned 5cm from the source, or:
10 1cm-Al that has 1m spacing between each 1cm-Al pair

Is not the same thing...since beta particles has a finite range in pure air.

5. Jan 6, 2008

### prochatz

Suppose we have two identical aluminium foils and a source that emits a vertical beam of beta particles (Sr-90). Suppose that I place a G.M. detector in a distance of 6cm over the source. Then, I do two procedures:

a) I place the two identical Al-foils very close each other in the distance of 3cm from the source.

b)I place the first Al-foil in the distance of 2cm from the source and the second one in the distance of 4cm from the source.

Will I notice any difference in the counts of the G.M. scintillator? In other words, do the two procedures absorb equally the beta particles?

6. Jan 6, 2008

### malawi_glenn

you should get a very small difference, since we have only magnitudes of a few centimeters.

you know how to calculate this theoretically?

I dont remember excactly, was a time since i did basic nuclear experiments, but I belive that average beta particles has a range of like one meter in air.

http://trshare.triumf.ca/~safety/EHS/rpt/rpt_2/node23.html

7. Jan 6, 2008

### prochatz

Isn't it weird? In both the previous procedures, beta particles are traversing the same distance in air and two Al-foils. Shoudn't the counts be the same?

8. Jan 6, 2008

### malawi_glenn

the order plays role too.

If you have 1cm Al then 5cm air or vice versa etc, makes a small difference.

The mass stopping power depends on the incoming energy of the radiation, so if the particle exits the source with 5MeV then enters air, you have a specific value of the mass stopping power in air, and after passing the 5cm of air, you will have a specific value of the energy that enters the 1cm Al and another specific value of the mass stopping power in Al.

But as I said, it is a very very small difference in this case.

Have you worked with this theoretically as a preparation of this lab?

Last edited: Jan 6, 2008