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