Radiative processes included when using the PAIRBREM card

Dear experts,

I am running a simulation using the PAIRBREM card to obtain a spectrum of X-rays produced by bremsstrahlung of primary protons injected into a thick-target (see post Proton bremsstrahlung).

Continuous emission of X-rays can be produced in proton–atom collisions by nuclear bremsstrahlung (NB), atomic bremsstrahlung (AB), secondary-electron bremsstrahlung (SEB), and quasi-free-electron bremsstrahlung (QFEB). Which of these radiative processes are included in FLUKA?

Thank you in advance,

Sergio

Dear Sergio,

Thanks for your question.

Concerning Bremsstrahlung by muon and charged-hadron projectiles (p), in FLUKA you’ll get a photon energy spectrum following

\frac{\text{d}\sigma}{\text{d}\nu} \sim \frac{1}{\nu}\left[ 1 - \nu + \frac{3}{4} \nu^2\right],\qquad \nu = \frac{E_\gamma}{E_p},

where E_\gamma and E_p are the energies of the emitted photon and the kinetic energy of the projectile, respectively.

That should essentially correspond to Nuclear Bremsstrahlung in the list above, with a complementary screening/polarization term applied to it. Needless to say, if a delta ray (secondary electron) is produced in another interaction, it too will emit Bremsstrahlung (depending on EMFCUT settings) as per the postscript below.

It’s worth pointing out that muons and charged-hadron projectiles (p) of less than

E_\text{min}=m_pc^2\sqrt{\frac{2000}{Z_t}}\ \text{ GeV},

in a material with atomic number Z_t will not emit Bremsstrahlung in FLUKA in view of its low likelihood compared to e.g. ionization or even nuclear reaction processes. For protons in H, Al, and U, E_\textrm{min} is about 41.9 GeV, 11.16 GeV, and 4.4 GeV, respectively.

Cheers,

Cesc

PS: for electron (and positrons) FLUKA will give you electron-nucleus and electron-electron Bremsstrahlung.

Dear Cesc,

Thank you very much for your reply. It helped to better understand why I am only getting a few photons in my proton bremsstrahlung simulations, complementing the reply I got from Andreas Waets to my previous post (Proton bremsstrahlung - #6 by anwaets).

Cheers,

Sergio