Trouble using the Bethe Formula

In summary, the speaker is struggling to use the Bethe formula to calculate stopping power for alpha particles. They have tried using the non-relativistic version from Wikipedia, but keep getting incorrect answers. They suspect the issue may be with the units of the permittivity, but after receiving help from others, they realize they made a mistake when looking up the unit of Coulomb.
  • #1
septemberskies
2
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?
 
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  • #2
You need to show us how you get the dimensions you see. One wild guess [itex]\beta [/itex] is non-dimensional.
 
  • #3
isn't [itex]mc^2[/itex] energy? So [energy]-1
then [itex]\Big( \frac{z^2 e^2}{4 \pi \epsilon_0} \Big)^2[/itex] has [force]2* [lenght]4 = [energy]2 * [length] 2 (distance times force = work = energy)
and finally [itex]n[/itex] has # / [length]3

The result is:
[energy]-1 [energy]2 [length]2 [length]-3 = [energy]/[length] for what I see...
 
  • #4
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.
 

Related to Trouble using the Bethe Formula

What is the Bethe Formula and how is it used?

The Bethe Formula, also known as the Bethe-Bloch Formula, is a mathematical equation used to calculate the energy loss of a charged particle passing through a material. It is commonly used in particle and nuclear physics to study the interactions of particles with matter.

Why do scientists encounter trouble when using the Bethe Formula?

While the Bethe Formula is a useful tool, it can become problematic when applied to certain scenarios. For example, it assumes that the particle is traveling at a constant velocity, which may not always be the case. It also does not account for the effects of multiple scattering, which can lead to inaccuracies in the calculated energy loss.

How can scientists address the limitations of the Bethe Formula?

To address the limitations of the Bethe Formula, scientists can incorporate corrections or modifications to the equation based on the specific scenario they are studying. This may include accounting for the particle's velocity or incorporating additional factors to account for multiple scattering.

What are some alternative equations to the Bethe Formula?

There are several alternative equations that scientists may use in place of the Bethe Formula, depending on their specific research goals and scenarios. Some examples include the Bethe-Heitler Formula, the Bethe-Block Formula, and the Rossi-Greisen Formula.

How can scientists ensure the accuracy of their calculations when using the Bethe Formula?

To ensure the accuracy of calculations using the Bethe Formula, scientists should carefully consider the limitations of the equation and incorporate any necessary corrections or modifications. They should also validate their results through experimental data and compare them to alternative equations to check for consistency.

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