Fe 56 heavy ion energy sampling from a histogram file

Source Definition
1

Dear FLUKA experts,

I am trying to simulate an Fe56 heavy ion source using the new source.f routine and the HEAVYION option in the BEAM card. I am sampling the energy from a histogram file.

I have set:

heavyion_atomic_number = 26
heavyion_mass_number   = 56
heavyion_isomer        = 0

energy_logical_flag = .true.

My spectrum contains the total kinetic energy of the Fe56 ion in MeV.

Should I use:

momentum_energy = sample_histogram_momentum_energy(
     &        "fe_spect.dat", "MeV" )

or should I divide the sampled value by the mass number

momentum_energy = sample_histogram_momentum_energy(
     &        "fe_spect.dat", "MeV" ) / 56.0D0

I would like to confirm how momentum_energy is interpreted for a heavy ion in this case whether the value should be the total kinetic energy of the ion or the kinetic energy per nucleon.

Thank you for your guidance.

Warm regard,
Dibi

3

Dear Dibi,

For a HEAVYION beam, the energy (or momentum) is expressed per nuclear mass unit, not as the total kinetic energy of the ion, as written in source_newgen.f:

! For heavy ions values are per nuclear mass unit.

This means that for your histogram file, containing the total kinetic energy of the Fe-56 ion, you should divide the sample value by the precise nucleus mass expressed in nuclear mass units of 55.936 (due to the excess mass). This assures you will have correct tracking in magnetic fields.

Best regards,
Barbara