Dear colleagues,
In the setup I have implemented, I have charged particles (40 GeV positrons) propagating in a magnetic field in vacuum. I enabled the emission of synchrotron radiation via the SYRASTEP card, enabling it in the two regions MAG0 and MAG1, and setting a threshold energy of 1 eV (the lowest available value according to manual)
SYRASTEP 1.0000e-09 0 MAG0 MAG1
I am using a LYSO calorimeter to measure the energy of emitted photons. However, I noticed a strange behavior in the measured spectrum, showing a discontinuity at ~ 1 MeV energy (see below)
The same threshold effect is visible if I run the simulation with positron beam at 60 GeV.
I can run some more detailed study of this effect, for example by printing the energy of all synchrotron radiation photones emitted via mgdraw.f, USDRAW routine: what would be the ICODE to use for this process?
I am using a custom FLUKA-based executable to score the energy measured in the LYSO-based calorimeter. However, for debugging purposes maybe it will be easier for you to just use the DETECT card for this? If necessary I can share with you the application!
The discontinuity is given from your thresholds: you apply a production and a transport cut equal to 1 MeV. Therefore, all the particles whose energy is lower than 1 MeV will deposit all their energy when they touch a material. If you want to have more realistic results, you need to change your EMFCUT cards.
For what concerns synchrotron radiation photons, indeed most of them are below this threshold.
Consider the critical energy formula in case of e+/e-:
E_c = 6.63E-7 * p[GeV]**2 * B[T]
In your case, you should have the critical energy equal to 784 keV for primary positrons entering in your magnetic field perpendicularly. Therefore, most of the SR photons will be anyway below the 1 MeV threshold and should not even be able to arrive at the detector.
Dear Daniele,
thanks! You are absolutely right, I really did a dummy mistake
I was fixing the threshold before, looking at the calorimeter, but I forgot to change it after implementing synchrotron radiation effects! Fortunately I can play with materials/regions to distinguish these.
