Re: FLUKA: missing energy

[paola sala <paola.sala@cern.ch>]

Dear Gregor,
The 'missing' energy comes from the variations in nuclear binding energies
due to nuclear reactions. It is usually positive, since most nuclear
reactions are endothermic (very roughly,  about 8 MeV are spent  to produce
each secondary nucleon). However, low energy neutrons can be  captured
without emission of secondary hadrons ; in this case the reaction is
exothermic, and about 8 MeV per capture are emitted as gamma rays. The
detailed balance depends of course also on the target material and on the
target dimensions.  You can find a short discussion and some examples in
the  A.Ferrari presentation at the Calor2000 conference :
http://fluka.web.cern.ch/fluka/talks/cal-1.html
                                        Ciao
                                        Paola

Gregor Wagner wrote:

> Dear Fluka-users,
>
> I am using a beam of neutrons as primary particles. For every run I get a
> large value of 'missing' energy in the run statistics table for deposited
> energy per beam particle:
>
> e.g.: for a beam of 140 MeV neutrons 33.5% of the deposited energy is
> 'missing'
>
> Neutron beams of lower energies cause even a negative value of
> 'missing' energy. In this case, the energy deposited by EM-cascades and
> by low energy neutrons is much larger than the energy of the primary beam
> particle:
>
> for example:
> 4.200E-05 GEV (100.%) DEPOSITED PER BEAM PARTICLE  OUT OF WHICH
> 1.488E-04 GEV (****%) BY EM-CASCADE,
> 2.464E-11 GEV ( 0.0%) BY PARTICLES BELOW THRESHOLD,
> 4.837E-05 GEV (****%) BY LOW ENERGY NEUTRONS,
> -1.552E-04 GEV (****%) MISSING.
> all other entries are zero
>
> if the beam energy is further decreased (1E-8 to 1E-6 GeV), the energy
> deposited by EM-cascades stays in the range from 1.E-4 to 2.E-4 GeV.
>
> Does anybody know, where these 'missing' energy values could come from?
> And what is the reason, that the energy deposited by electromagnetic
> cascades is larger than the beam energy?
>
> Regards,
> Gregor
>
>