# Alpha and beta particles in gas ionization

1. Oct 14, 2012

### scientifico

Hello, why alpha particles are better at ionizing gases than beta particles ?
shouldn't the negative particles repel more electrons ?

thanks

2. Oct 15, 2012

### mathman

Try to be more specific. What do you mean by "better"?

3. Oct 15, 2012

### bcrowell

Staff Emeritus
I assume "better" refers to the fact that dE/dx is much higher.

This is basically because Rutherford-like scattering has a cross-section that varies as $v^{-2}$ (because high-velocity particles aren't deflected very much). MeV alphas have much lower velocities than MeV betas, and therefore the cross-section for an electron to scatter off of them is much higher.

There are lots of other factors involved (e.g., the square of the charge), but this is the dominant one in this comparison. For more detail: http://en.wikipedia.org/wiki/Bethe_formula

4. Oct 15, 2012

### Staff: Mentor

The magnitude of the force between two negative charges is the same as the force between one negative and one positive charge - the direction is different, but that does not matter here.
For the comparison alpha<->beta, see bcrowell's explanation.