Method

This set of routines generates the photon-induced fission in the nuclei of heavy materials. The code is a straight translation into the GEANT style of the corresponding code from the GHEISHA Monte Carlo program.

The information contained in this chapter is mainly taken from the GHEISHA manual to which the user is referred []. In fissionable elements the inelastic reaction of photons may be accompanied by the fission of the nucleus. This channel is taken into account only when the nuclear mass is between 230 and 240. The fission cross-section for uranium is tabulated, and for other elements the parameterisation of the A-dependence at 3 MeV neutron energy is used:

$\sigma$_f( 3 MeV ) = - 67.0+38.7 &sp;Z^4/3 A

which implies that the fission may occur only for $Z\; \ge 90$ . The fission products are generated in an approximate way. The giant resonance effect is included here as nuclear photoabsorbtion. The photo-fission is activated by the data record PFIS. Secondaries coming from the interaction of the virtual photon with the nucleus will be in the GEANT temporary stack. If IPFIS=2 the secondary particles will not be generated and the energy of the photon will be summed to DESTEP. A table with the photo-fission cross-sections as a function of the energy is put in a bank at initialization time for all the materials with A bigger than 230. See material bank structure for details.

PHYS250