# Bethe formula question

1. Jul 2, 2009

### jbb88

Im trying to use the Bethe formula (http://en.wikipedia.org/wiki/Bethe_formula) to find dE/dx for a particle through a material, but Im not getting the units to work out. In the part of the formula with (e^2/4PiEpsilon)^2, how should I convert this correctly? Those units are J*m, so can I just multiply by 100 to get it to J*cm and divide by 1x10^-6 to get it into MeV*cm?

2. Jul 2, 2009

### humanino

At first glance, wikipedia's formula looks suspicious, although they may be equivalent, I always use : the particle data book
You may find your coefficient in table 27.1 if you really want wikipedia's formula.

3. Jul 2, 2009

### jbb88

Thanks, ill use that. The one thing Im not sure of is the delta part of that equation. How do I figure out what to use for delta(beta gamma)?

4. Jul 2, 2009

### humanino

If you need this term at high energy, it is defined (and discussed) in 27.2.2
Also, look at "without delta" curve label in 27.1
For $\beta\gamma$<10 the effect is rather small