1. NAME AND TITLE

MICAP: A Monte Carlo Code System for Analysis of Ionization Chamber Responses.

AUXILIARY ROUTINES

RDNDF: Reads and processes ENDF/B-formatted cross section files.

MICRO: Manipulates the microscopic cross section data sets.

MACRO: Creates macroscopic cross section data sets.

NEUTRON: Neutron transport module.

RECOMB: Calculates the saturation effects correction data.

HEAVY: Recoil heavy ions and charged particle transport module.

PECSP: Generates photon and electron cross section and material data.

PHOTPREP: Generates photon source input for the PHOTON module.

PHOTON: Photon and electron transport module.

DATA LIBRARIES

ENDF/B-V data pre-processed through the RESEND5-LINEAR/SIGMA1 programs so that all cross section data are linearly interpolable over the entire energy range have been included in the package for the following nuclides: hydrogen, carbon, nitrogen, oxygen, fluorine, aluminum, argon and calcium. Pair production data is also included for input to PESCP.

2. CONTRIBUTOR

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

3. CODING LANGUAGE AND COMPUTER

Fortran IV and Assembler Language; IBM 3033 (P00261I303300).

4. NATURE OF PROBLEM SOLVED

MICAP has been developed to determine the response of a gas-filled cavity ionization chamber or other detector type (plastic scintillator, calorimeter) in a mixed neutron and photon radiation environment. In particular, MICAP determines the neutron, photon, and total response of the detector system. The applicability of MICAP encompasses all aspects of mixed field dosimetry analysis including detector design, pre-experimental planning and post-experimental analysis. MICAP is a modular code system developed to be general with respect to problem applicability. The transport modules utilize combinatorial geometry to accurately model the source/detector geometry and also use continuous energy and angle cross section and material data to represent the materials for a particular problem.

5. METHOD OF SOLUTION

The calculational scheme used in MICAP follows individual radiation particles incident on the detector wall material. The incident neutrons produce photons and heavy charged particles, and both primary and secondary photons produce electrons and positrons. As these charged particles enter or are produced in the detector material, they lose energy and produce ion pairs until their energy is completely dissipated or until they escape the detector. Ion recombination effects are included along the path of each charged particle rather than applied as an integral correction to the final result. The neutron response is determined from the energy deposition resulting from the transport of the charged particles and recoil heavy ions produced via the neutron interactions with the detector materials. The photon response is determined from the transport of both the primary photon radiation incident on the detector and also the secondary photons produced via the neutron interactions. MICAP not only yields the energy deposition by particle type and total energy deposited, but also the particular type reaction, i.e. elastic scattering, inelastic scattering, (n,p),(n,alpha),etc., which produced the particle depositing the energy. Physics to handle ENDF/B-V partial cross section data have been incorporated in the neutron transport module to account for all processes which may contribute to the output signal. The transport modules utilize continuous angular distribution and secondary energy distribution data when selecting the emergent direction and energy of a particle. Furthermore, reactions are treated as discrete and are allowed to occur with any of the constituent nuclides comprising a mixture. Finally, MICAP incorporates a combinatorial geometry package and input cross section processors to eliminate restrictions in the modeling capability of the code system with respect to geometry, physical processes, nuclear data and sources.

6. RESTRICTIONS OR LIMITATIONS

Present dimensions limit the number of media to 10 in PHOTON. Dimensions restrict the number of media to 15 and the number of nuclei per medium to 11 in the RECOMB module. The RDNDF module is currently configured to process one nuclide at a time.

7. TYPICAL RUNNING TIME

Running time is problem dependent. The sample problem requires no more than 25 seconds in any individual module.

8. COMPUTER HARDWARE REQUIREMENTS

MICAP is operable on the IBM 3033 computer. Core storage required varies among modules. Typical problems require approximately 1000 K bytes of memory.

9. COMPUTER SOFTWARE REQUIREMENTS

The Fortran H-Extended Enhanced compiler was used under MVS.

10. REFERENCES

a. Included in documentation:

J. O. Johnson and T. A. Gabriel, "A User's Guide to MICAP: A Monte Carlo Ionization Chamber Analysis Package," ORNL/TM-10340 (January 1988).

b. Background information:

J. O. Johnson and T. A. Gabriel, "Development and Evaluation of a Monte Carlo Code System for Analysis of Ionization Chamber Responses," ORNL/TM-10196 (July 1987).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one DC6150 cartridge tape in TAR format, with source programs, sample input and output.

12. DATE OF ABSTRACT

June 1988.