MICAP (A Monte Carlo Ionization Chamber Analysis Package) [], [] is a Monte Carlo system to analyze ionisation chamber responses. As a standalone program it contains the code for formatting the cross-section files, neutron and photon transport, the geometry definitions and the code for the chamber response. In GEANT, only the sampling of the neutron interactions from the already prepared cross-section file is included. The interface between GEANT and MICAP has been extracted from GCALOR package[] by C.Zeitnitz and T. Gabriel.
When using GEANT-MICAP interface the low-energy
neutrons are handled in MICAP routines.
Other hadrons and high-energy neutrons are
passed to FLUKA interaction routines.
For low-energy neutrons,
the total cross-section is given by MICAP
and if the neutron interaction is chosen by GEANT
tracking routine,
GMICAP reads the cross-section for neutron interactions
processes,
samples and generates the interaction and the returns the
secondary particles (nucleons, heavy fragments, or
photons) to GEANT. Information on the recoil
nucleus (atomic number AMED, charge ZMED and
kinetic energy ERMED) can be found in MCRECO
common block. The program flow is shown in figures
and .
Figure: Program flow for calculation of the distance to
the next interaction point
Figure: Program flow for generating secondary particles
MICAP uses pointwise cross-section data (as a difference to so called group cross-sections where the data are averaged over certain energy intervals). This method has the advantage that the resonances are not smoothed by averaging the data. The neutron cross-section are available for the following isotopes:
| Hydrogen (bound) | Sodium | Copper |
| Hydrogen (free) | Magnesium | Molybdenum |
| Lithium (5) | Aluminium | Barium |
| Lithium (6) | Silicon | Tantalum |
| Boron (10) | Chlorine | Tungsten |
| Boron (11) | Argon | Lead |
| Carbon | Calcium | Uranium (235) |
| Nitrogen | Chromium | Uranium (238) |
| Oxygen | Iron | |
| Fluorine | Nickel |
If the cross-sections are not found for some of the defined materials, a warning is printed first at the initialisation time telling which cross-section are used (the closest Z available) instead. Then, an additional warning is printed each tracking step. parbox # #
F.Bruyant