Calculating the ionization rate in the Interstellar medium?

[unicornflyers]

I hope putting this in the high energy section is the right section (if not, please let me know which would be more appropriate!) I felt this was appropriate since the work I am doing is high energy astrophysics.

So I'm doing some research this summer, and my tasks were to take some data from satellite observations on cosmic rays, and find the Cosmic Ray intensity (sometimes referred to as flux, but is also known as the Cosmic ray spectrum) for several species. This includes protons, electrons, helium, and carbon.

The units on the intensity are $ [particles.m^{-2}.s^{-1}.sr^{-1}.(GeV/nuc^{-1}]$.

The next task is to find the ionization rate. Here is where I am confused.

I have these equations for intensity. I do not know how to get an ionization rate out of this. I know, in principle, what I should do to start, and that is the following:

1) compute the energy in the material per unit thickness
2) divide by the average ionization potentialBut here is my question. For the Interstellar Medium (ISM), what material are we considering to compute the energy? And how would we compute this per thickness?

Any time I have ever seen ionization potential, it was just looking it up on the periodic table. How do we actually go about computing the ionization potential?

Finally, to get the ionization rate, do we divide the energy by the ionization potential?

Thank you all!

 

[Astronuc]

But here is my question. For the Interstellar Medium (ISM), what material are we considering to compute the energy? And how would we compute this per thickness?

One more or less answered that question earlier in the OP.

some data from satellite observations on cosmic rays, and find the Cosmic Ray intensity (sometimes referred to as flux, but is also known as the Cosmic ray spectrum) for several species. This includes protons, electrons, helium, and carbon.

In addition to particles, one also has X-ray and gamma radiation. To get reaction rates, one would use the integrated product of the flux and the cross-section for the particular reaction.

Here is an article on ISM ionization rates with citations.
http://www.pnas.org/content/103/33/12269.full

See also - http://www.astronomy.ohio-state.edu/~pogge/Ast871/Notes/Intro.pdf for some background