Trouble using the Bethe Formula

Click For Summary
The discussion revolves around difficulties in applying the Bethe formula for calculating stopping power of alpha particles. The user initially struggles with unit conversions, particularly receiving unexpected results in seconds squared instead of the correct units. After analyzing the formula, they identify a misinterpretation of the unit for Coulomb, which was read incorrectly, leading to the confusion. Once this mistake was corrected, the calculations aligned properly, indicating the importance of accurate unit interpretation in physics equations. The conversation highlights the collaborative effort in troubleshooting complex scientific problems.
septemberskies
Messages
2
Reaction score
0
So I'm doing research with a professor and he wants me to use the Bethe formula to calculate stopping power for alpha particles of various energies, but I'm having a lot of trouble using it, and I figured I'd ask here before I bothered him.
He wanted me to use the non-relativistic version listed on Wikipedia (from Sigmund 2006, and I've seen it other places in the same form, so I don't think it's a problem with the formula). Here it is: https://en.wikipedia.org/wiki/Bethe_formula
I was getting very confusing answers, so I tried just going through the formula with nothing but the units and seeing if they worked out. The units we want for dE/dx are eV/m or eV/cm (or Joules/distance, I guess), correct? The main issue I'm having is that, with the units, I keep getting an answer per seconds to the TENTH, when it's only supposed to be seconds squared, and I cannot for the life of me figure out where the extra s^-8 is coming from. My first instinct is that it's from the units of the permittivity squared, but the rest of the units of the permittivity seem to work out fine.
Any idea where I'm going wrong?
 
Physics news on Phys.org
You need to show us how you get the dimensions you see. One wild guess \beta is non-dimensional.
 
isn't mc^2 energy? So [energy]-1
then \Big( \frac{z^2 e^2}{4 \pi \epsilon_0} \Big)^2 has [force]2* [lenght]4 = [energy]2 * [length] 2 (distance times force = work = energy)
and finally n has # / [length]3

The result is:
[energy]-1 [energy]2 [length]2 [length]-3 = [energy]/[length] for what I see...
 
It turned out that I made a really stupid mistake. When I was looking up Coulomb in base units since I don't know it offhand, I apparently misread it as A/s instead of A*s. Everything works out now. Thanks for replying, everyone. It helped me narrow down to the part of the equation I was messing up on.
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
867
Replies
3
Views
6K
  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 1 ·
Replies
1
Views
11K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K