Fission energy simulation

we have an application where we simulate an accelerator driven multiplicative system (ADS) with Geant4. We use Neutron_HP and we score the energy components of the fission process n(U235,F). According to the literature we should have

  • Instantaneously released energy
    • Kinetic energy of fission fragments 169.1
    • Kinetic energy of prompt neutrons 4.8
    • Energy carried by prompt γ-rays 7.0
  • Energy from decaying fission products
    • Energy of β−-particles 6.5
    • Energy of delayed γ-rays 6.3
    • Energy released when those prompt neutrons which don’t (re)produce fission are captured 8.8
  • Total energy converted into heat in an operating thermal nuclear reactor 202.5
    • Energy of anti-neutrinos 8.8
  • Sum 211.3

Running the simulation with Geant4, we find

1 gamma and 2.44 neutron / fission

  • neutron Mean Energy : 1.97 => 4.80
  • gamma Mean Energy : 0.8
  • fission Mean Energy : 164.4
  • total Mean Energy : 171.6

If you do not count the (n,g) reactions, we should have 193.7 MeV while we only have 171.6.

  • The FF kinetic energy seems to be too low 164.4 instead of 169.1
  • The neutron kinetic energy is OK
  • The gamma energy is way too low
  • There is no production of beta rays

We could enable the production of FF, but it is stated in the doc that these are not decayed, so we still would not get the beta, and this would not help the prompt gamma.

Thanks in advance for your help. Best regards, Federico Carminati

Hello, Federico,

I would compare results for QGSP_BIC and QGSP_BIC_HP for better understanding of the problem.


Hello Vladimir,
most of these fissions if not all are <20MeV, so it most a problem with NeutronHP. Best,

HI Federico,

I have run Hadr03 with the attached macro and got the following.
(please see readme of Hadr03 to well understand what this rather simple example does)

  • from histo 10, we can say that total instantaneously released energy is < Q > = 179.4 MeV

  • from histo 7, we can say that there are 2 fragments (obvious !) of 84.57 MeV each. Total = 169.14 MeV

  • from histo 3 : there are 2.43 prompt neutrons with energy 1.97 MeV. Total = 4.79 MeV

  • from histo 2 : 8.742 prompt gamma of 625 keV. Total = 5.46 MeV

    So, fragments + neutrons + gamma = Q = 179.4 MeV

nFission.mac.txt (743 Bytes)

Thanks Michel,
is this with GENERATE_FISSION_FRAGMENTS or with WENDT? Best,

with default neutronHP package and GENERATE_FISSION_FRAGMENTS

HI Federico,

I have continued the previous exercice with a slightly modified Hadr06 : kill the prompt neutrons after to have collected their kinetic energy.
In this situation, Hadr06 output gives directly the energy balance of a single fission, including the decay of the fragments.
I joint macro and output. As you can see, the total energy deposit in an " infinite " medium is ~192 MeV/fission and the energy carried out by neutrinos is ~8 MeV/fission.
fission.mac.txt (364 Bytes)
fission.out.txt (2.4 KB)