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| Geant 3.16 | GEANT User's Guide | PHYS240 ##
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Author(s) : F. Carminati Submitted: 20.12.85
Origin : H.C.Fesefeldt Revised: 17.12.92
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|CALL GPFISI |
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GPFISI computes and stores in the appropriate bank (see JMATE data structure) the value of the photo-fission cross sections as a function of the energy for a given material. It is called at initialization time by GPHYSI.
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|CALL GPFIS |
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GPFIS is called by the tracking routine GTGAMA every time a photon-induced fission is to happen. It generates the final state particles. A call to GUHADR is performed if IPFIS (which is the variable set by the PFIS data record) is equal to 1. If the GHEISHA interface is used, a fission is forced. The secondaries from the photo-fission are always generated if IPFIS is equal to 1, irrespective of the value of IHADR.
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 GHEISHA routines PFISS and CALIM have been used.
The information contained in this chapter is mainly taken from the GHEISHA manual to which the user is referred [bib-GHEI]. 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 bigger than 230. The fission cross-section for uranium is tabulated, and for other elements the parameterization of the A-dependence at 3 MeV neutron energy is used:
4/3
sigma (3Mev) =-67. 0+38. 7Z A
f
which implies that the fission may occur only for Z>=90. The fission products are generated in an approximate way. The photon is replaced by a pion of random charge with the same kinetic energy. Then the GUHADR routine is called to generate a pion-nucleus inelastic scattering. The photo-fission is activated by the data record PFIS. If IPFIS=1 has been specified, secondaries coming from the interaction of the virtual photon with the nucleus will be in the GEANT temporary stack. If IPFIS=2 has been specified, then 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.