Microdosimetry of Proton

Dear fluka developers and users,
My name is Victoria, I started working with proton microdosimetry and I’m having trouble finding the smallest targets and lowest energies that fluka can calculate with this type of beam. My tests with low energies (40 MeV) in conjunction with a micrometer sized target are not generating results.
When I just decrease the energy, I get results, but when combined with smaller target dimensions, it doesn’t produce data.
I would like to know if there is a minimum size limit for a target being hit by low energy proton beams and what these limiting factors would be.
Thanks in advance for the help!

Dear @victoria.rapos

Thank you for your question.

Could you please share me the fluka input file, please?
I would like to see what you intend to simulate in more detail.


Thank you so much for replying!!
I didn’t finish the input, I was testing the smallest target sizes and lowest energies, as I’m running on my personal computer, I used few primary particles. The plan is to simulate beams of proton passing through cells in very small doses. I’m sending the inputs so far.
Thank you.
menoralvo.inp (1.2 KB)
menorenergia.inp (1.2 KB)
modelo microdosimetria proton.txt (2.2 KB)

Dear @victoria.rapos,

Sorry for the delay in replying!

Just a few comments about your inputs.

  1. In menoralvo.inp: the usrbin that you are using is too big compared to the size of your water target. you can observe it in the following picture:

Here you can observe the bins of your usrbin, where only the first bins in z occupy one small part of your target. Try to redefine it according to your needs. You can see an example here:

Where I defined this usrbin:
Screenshot from 2023-02-06 11-32-04

One comment about the usrbin. In the inputs, you sent me you are interested in obtaining the “fluence” of the protons. In case you wanted to do this, it is correct. Still, if you were actually trying to get the energy deposited by all the particles in the regions occupied by the usrbin, then you need to use “Energy”, as you can see in the screenshot above.

Here you have info related to how to use usrbin properly:

  1. In menosenergia.inp you have a similar problem defining the usrbin, but with an extra due to the energy for your proton beam:

Here, you can see that your protons are not even moving beyond your first bins in z again.
Define the usrbin for this case to have a resolution according to the problem.

Let me know if this helps. In case you need more advice, don’t doubt in asking.

Have a nice week,


P.d: If you want to learn how to see the usrbin in the geometry tab of flair, you can take a look at the following slides (page 18 mainly):

And for more info about flair:

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