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1. Oct 22, 2016

### m_p_w

This might be a very stupid question :(, but I am confused.

So I did an experiment.
we had radioactive material which was emitting beta particles, and we were using geiger counter to measure pulses (ionized beta particles). We were supposed to measure the time it takes for the geiger counter to reach 1000 pulses and time difference by adding aluminum foils (thicker aluminum foil = longer time).

I am confused about two things,
-How it is possible that aluminum foil is able to stop beta particles? (what happens to beta particles in aluminum(are they just reflected from aluminum nucleus or can they become also outer-shell electron of aluminum atom, can beta particle get ionized in the aluminum foil (steal an electron from aluminum atom)?

-Are ionized beta particles dangerous? (ionized alpha particle are not because they become helium, what happens with beta particles?)

Last edited: Oct 22, 2016
2. Oct 22, 2016

### secur

Beta particles aren't "ionized". They are "ionizing", perhaps that's what you mean. But alpha particles are ionized, they're helium atoms with a +2 charge - bare nuclei.

Your beta particles are probably electrons - "beta minus" (might be positrons, I doubt it). You seem to be thinking, incorrectly, they're protons - which would be ionized (+1). An electron hitting aluminum ... I suppose it becomes an outer-shell electron, making a +1 ion, which would soon get lost. Overall, aluminum will acquire a negative charge from beta radiation, soon lost to the environment.

Any such radiation, alpha or beta, will hurt you in sufficient quantities. For one thing they're pretty fast (carry energy and momentum), also they ionize atoms of your flesh. Both these things are disrupting. Obviously your lab experiment is designed to be safe - I hope - by involving a very small amount of radiation and/or appropriate shielding.

3. Oct 22, 2016

### m_p_w

So aluminum would acquire a beta particle (and loose it to the environment as free electron), and not just bounce it off to different directions?

4. Oct 22, 2016

### secur

I suppose many would get absorbed, giving the aluminum negative static-electricity charge, while some simply bounce off. But, sorry, others know those details much better than I do, so let them answer. I can say that such static electricity wouldn't be dangerous.

5. Oct 23, 2016

### vanhees71

Sure, $\beta$ radiation (electrons) are partially absorbed by material like a aluminium foil.

6. Oct 23, 2016

### houlahound

Not sure what the mean free path of an electron in air at STP is but I assume it is short. Dusty room even shorter.

7. Oct 23, 2016

Every time a radioactive particle interacts with an atom, eg by ionising it, the energy needed to ionise the atom is lost from the particle and as a result the particle loses energy and slows down
. Eventually the particle will have lost so much energy that it becomes non ionising and in effect we can say that it has reached the end of its range. The denser the medium through which the particle travels the greater the number of collisions per unit length and the shorter the range.

8. Oct 23, 2016

### DarkBabylon

One thing I can read from the web, and is unsurprising to me, that free electrons would be stopped by a few millimeters of aluminum. Basically shielding wouldn't be hard at all, at worst it is probably a trip costing 2\$ at least to the supermarket and back.