Different dE/dx values by using Precision and Hadrontherapy

Dear FLUKA experts,

I tried to simulate 12C ions with a water target (incident kinetic energy 400 MeV/u).

image

I used two different models in the DEFAULTS card, i.e. Precision and Hadrontherapy.
Then I tried to output the stopping powers, dE/dx by using the DELTARAY card.

image

But the output of dE/dx by using the two models differ a lot, as shown below.

Is this correct? Which one is more reliable? Can anyone help me understand the physics?

One more question, which of the following is the printed dE/dx from the DELTARAY card (the 2nd column)?


or

Hello Kaiwen,

What is printed in the output file is the restricted stopping power (following the 2nd expression you point above).

Using DEFAULTS with HADROTHE, the delta-ray production threshold is 300 keV.

Using DEFAULTS with PRECISIOn, the delta-ray production threshold is 100 keV, i.e. more of the ionization losses are sampled explicitly as delta rays instead of in an aggregate manner along the step via a stopping power, hence the PRECISIO stopping power is lower than that with HADROTHE in your plot.

You may also want to take a look at this post.

Hope this helps,

Cesc

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Dear Cesc,

Thanks a lot for your explanation!
But according to Table 7.1 of the FLUKA manual, the default value of delta-ray production threshold is 100 keV for both DEFAULTS and PRECISIOn (WHAT(1) of DELTARAY is 0.0001). I’m not sure whether I understand the Table correctly.

Best,
Kaiwen

Hello Kaiwen,

I fail to find this table in the FLUKA manual as distributed in https://fluka.cern , where instead you’ll find (the “Delta ray production” line is what matters here):

and

If you run a quick input simply changing the DEFAULTS from PRECISIO to HADROTHE and you look for differences in the output file you’ll retrieve the aforementioned values (note that delta-ray production cuts are printed as total energy i.e. rest mass + kinetic energy).

With kind regards,

Cesc

Dear Cesc,

Thank you very much for your explanation.
I ran a quick input using HADROTHE and indeed it showed
" ***** Delta ray production activated above 3.0000E-04 GeV ***** "
But is this a typo for DELTARAY in the online manual, where it shows

You are right, it shall be fixed in the note 9 of the DELTARAY card. Thanks for that!

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Thanks, well spotted! Will be amended and included in the manual for the next release.

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