Muons from cosmic radiation at sea level

Scoring
1

Dear Fluka experts,

I’m trying to study the response of NaI(Tl) detector on muon radiation at sea level. As a first step I tried to model muon spectrum at sea level by using built-in cosmic rays source. As an input I used slightly modified files from Fluka CGR example, and files that were generated by ‘atmloc’ program. (all files that I used for this purpose are in ‘Input.zip’ archive that I attached to the message). To score muon flux at sea level I used USRYIELD card and USRBDX card (the resulting files are in ‘Output.zip’ archive). The resulting spectra for Mu+ and Mu- that I received for the USRYIELD card are in the picture. When trying to interpret the result of modelling I’ve faced with some complications. I compared the result of modelling with experimental results provided in several papers (I’ve attached the picture with the result from paper https://doi.org/10.1103/PhysRevD.58.054001 ). The result of modelling does not look like experiment at all. Could you, please, help me understand, if I on the right path:

  1. As far as I understood from the manual the result of USRYIELD is plain double differential of number of particles per primary: dN/(dE*d0), where E is energy and 0 is an angle. Is it correct to interpret the result as dN/dE integrated over given interval for the angle 0?
  2. Is it correct to interpret the result of USRYIELD modelling for my case as muon spectrum at sea level that can be further used as input spectrum to determine the detector response? Or should I make some processing for the modelling spectra in order to transform it to true muon spectra at sea level?
  3. Can I interpret the result of modelling as vertical component of muon flux averaged over given angle interval?

Thank you in advance,
Alexy

Input.zip (19.7 KB)
Output.zip (315.0 KB)

atmloc_input_1
atmloc_input_11557×864 30.9 KB

atmloc_input_2
atmloc_input_21538×883 31.4 KB

USRYIELD_output
USRYIELD_output1920×812 103 KB

Predictions_from_paper
Predictions_from_paper768×724 42.8 KB

3

Dear @Alexy,

Thank you for your question. I proceed to answer to the different points:

  1. In your input file, USRYIELD is set to calculate d2N/dE/dtheta/cos(theta), but unfortunately this option is discontinued as you can see in the FLUKA forum (7.22.94. USRYIELD — FLUKA Manual). Moreover, please note that in USRYIELD, the fluence is calculated as the proyection of the particle trajectory with respect to a fixed direction, instead of to the surface normal, which is probably what you may be looking for. Therefore, perhaps USRBDX might yield the desired result: d2N/dE/dtheta where theta is the solid angle between the normal and the particle, and theta bins is set to 1.

  2. The results of the USRBDX mentioned above produce an effective dN/dE, which can be used as input in the second leg of a two-step simulation. You need to use the source routine where the energy is sampled from an histogram.

  3. USRBDX outputs the double differential of the particle fluence as a function of the energy and solid angle. Setting the solid angle bins as 1 and proper maximum and minimum angles with respect to the normal, the result could indeed be considered as the vertical muon flux over the interval.

Please let me know if this is helpful.
Regards

Mario

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