1. NAME AND TITLE
COHORT-II: General Purpose Monte Carlo Radiation Transport Code System.
EXECT: Main Control Code.
INPUT: Input Data Processor.
SORCE: Primary Source Data Generator.
HTA: Particle Tracking and Scoring Code.
OUTPUT: Edit and List Code.
SECGAM: Secondary Gamma-Ray Source Data Generator.
RAND: FORTRAN Random Number Generator.
The original design of the COHORT code dates back to work done at General Dynamics, Fort
Worth, Texas, in 1962. Development continued in the COHORT series at Radiation Associates
(RRA), Fort Worth, and Brown Engineering (BE), Huntsville, Alabama, for NASA Marshall Space
Flight Center (1964). COHORT was further developed by RRA for Aerojet Nuclear Systems for
CCC-191/ACOH. The BE work resulted in CCC-169/CAVEAT. COHORT-II is a major revision
and modernization of the original COHORT (1966).
NASA Lewis Research Center, Cleveland, Ohio.
3. CODING LANGUAGE AND COMPUTER
FORTRAN IV; IBM 7094.
4. NATURE OF PROBLEM SOLVED
COHORT-II is a Monte Carlo general purpose shielding code which tracks neutrons and photons through flexible shield geometry configurations.
Printed output includes number fluxes that are averaged over regions and fluxes that are at
arbitrarily located point detectors. The volume averaged region fluxes can be sorted according to
arbitrary energy bins. The point-detector fluxes list uncollided (for isotropic sources only) and
scattered flux contributions separately and can be sorted according to their polar and azimuthal
angles of arrival at the detector as well as their energies. An estimate of the statistical precision is
included for both volume and point detectors. Energy integrated quantities such as dose rates,
heating rates, reaction rates, and fluxes greater than a given energy can also be computed for both
volume and point detectors by entering suitable response functions. Where only one type of
detector is of interest, the computation associated with the other type can be omitted to save time.
All scoring, both for volume and point detectors is performed by statistical estimation.
5. METHOD OF SOLUTION
Primary particles are generated from previously known spatial, angular, and energy distributions supplied by the user. The conventional code method is employed where individual particles are generated, tracked, and analyzed. The shielding geometry allowed is flexible with space divided into homogeneous regions bounded by surfaces describable by a general quadratic equation. Spherical, cylindrical, and rectangular parallelepipeds are allowed for the source regions. Biasing options include selection of source particles from preferred locations, energies, and directions. The exponential transform can also be used during particle tracking. Secondary gamma rays can be generated and placed on tape during a neutron problem to be tracked during a subsequent computer run. Variable dimensioning is employed for efficient use of computer storage.
The program does not require the user to handle tapes except when a leakage or a secondary
gamma-ray tape has been requested. A complete analysis of a typical reactor-shield problem would
require three separate Monte Carlo problems to be run on the computer. These runs would be used
to track and analyze, respectively, primary neutrons, primary photons, and secondary photons. A
physical source tape for the secondary gamma problem would be generated during the primary
6. RESTRICTIONS OR LIMITATIONS
The code requires input cross-section data in its own specialized format and cannot accept
multigroup cross-section data as used in conventional transport codes.
7. TYPICAL RUNNING TIME
No study has been made by RSIC of typical running times for COHORT-II.
8. COMPUTER HARDWARE REQUIREMENTS
COHORT-II is operable on the IBM 7094 computer.
9. COMPUTER SOFTWARE REQUIREMENTS
A FORTRAN IV compiler is required as well as the Overlay feature with a main link and five
dependent links. Variable dimensioning has been incorporated.
L. Soffer and L. Clemons, Jr., "COHORT-IIA Monte Carlo General Purpose Shielding
Computer Code," NASA TN D-6170 (April 1971).
11. CONTENTS OF CODE PACKAGE
Included are the referenced document and one (1.2MB) DOS diskette which contains the source
codes, data libraries, and sample problem input and output.
12. DATE OF ABSTRACT
September 1975; revised September 1982.
KEYWORDS: NEUTRON; GAMMA-RAY; MONTE CARLO; COMPLEX GEOMETRY