About modifying the energy cutoff value for nuclear reactions

Dear FLUKA experts:

Please forgive my intrusion. I would like to inquire about when the cutoff energy value for nuclear reactions (1.1 MeV/n) in FLUKA code could be modified. In fact, some reactions (such as D+3He) have considerable cross sections below this cutoff, which is quite important for calculating nuclear reaction physics.
The figure below shows the reaction cross section for a 3He beam bombarding a D target, with the horizontal axis representing the 3He energy in the laboratory frame.
I sincerely hope that FLUKA developers can resolve this issue as soon as possible. Thank you for your generous help and patient response. I wish you the very best .
屏幕截图 2023-11-10 193450

Dear Yu,

My apologies for the delay.

The 1.1 MeV/n cutoff below which no nuclear reactions generally occur is meant to (somewhat loosely) account for Coulomb barrier effects - at the very least to have a systematic rule from our general-purpose code perspective.

There are notable exceptions to this threshold:

  • Neutral kaons
  • Antineutrons
  • Deuterons (to accommodate for the d+D and d+T reactions with maxima in the order of 100s of keV)
  • For particular hadron + nucleus combinations, such as p+11B (which will be further refined in an upcoming release)
  • the trivial case where the user switches off nuclear reactions with a THRESHOLd card

For now, reaction cross sections below the 1.1 MeV/n cut are extended on a case-by-case basis, provided of course that our hadron-nucleus interaction model yields reasonable final-state predictions.

We take note of the 3He on D case for future detailed consideration.

Many thanks,


Dear Cesc
Thank you very much for your answer. Due to the existence of the Coulomb barrier, nuclear reactions below this barrier can occur through quantum tunneling effects. For certain reactions, such as D+3He and D+T, there is a significant resonant cross-section below the Coulomb barrier. Additionally, I would like to ask, what can I do now to change this situation? Or do I just have to continue waiting for the developers’ modifications?

Or do I just have to continue waiting for the developers’ modifications?