# GCR Atmospheric model - pressure and densities values doubt

Dear Fluka experts,

Based on the standard US atmosphere model of 100 layers available in the Fluka Cosmic Rays examples (also attached here), I’m trying to modify it to run some simulations with summer and winter atmospheres in a different location.

atmomat.cards (27.8 KB)

As I understood reading this post https://fluka-forum.web.cern.ch/t/use-of-the-mat-prop-card/49, the values of densities from MATERIAL card and pressures from MAT-PROP card are used by the code to evaluate the Sternheimer-Peierls formula at Normal Temperature and Pressure (NTP).

The ratios between densities and temperatures are constant in the atmomat.card model and if multiplied by the Rspec the constant is a temperature of ~288 K or 15 C in each layer.

``````T = rho*Rspec/P

where rho is the density (kg/m^3), P the pressure (Pascal), and Rspec 287.058 (J⋅kg−1⋅K−1)
``````

Is it possible to simulate an atmosphere with temperatures from -60 to 30 Celsius, changing the atmospheric pressure values of the MAT-PROP? This way, this constant between density and pressure will be broken. Could this lead me to a calculation error?

Jordi

Dear Jordi,

There is no specific motivation to keep the ratio you are referring to between density and temperature a constant. As mentioned in the post by Anton the densities in the different layers need to be accurately implemented to make sure the cross sections are correctly converted to mean free paths for proper particle transport. Then, the stopping power in the different layers is corrected for the density effect, first through evaluation of the Sternheimer-Peierls formula at Normal Temperature and Pressure (NTP) and then corrected back to the pressure (and by consequence temperature through the ideal gas law) you provided using the MAT-PROP cards. In this way it is certainly possible to simulate atmospheres with the temperature ranges you quote without errors, keeping in mind of course that in having the correct density profile is the most important.

If you are worried about possible boundary effects when going from one layer to another: of course this is inherent to the model in itself since the atmosphere is anyway sliced up in layers of with different properties. So in short I see no obvious reason why this would not be possible.

Hope this helps,

Andreas

(PS: I believe the ideal gas law equation should be T = P/(rho*Rspec)

1 Like

Dear Andreas,

The question appeared when, analyzing the atmospheric model found in Fluka examples, this constant pattern was detected. Thank you for your clarifications!

All the best,

Jordi