**1. NAME AND TITLE**

ACOH: Aerojet COHORT Monte Carlo Code System.

**AUXILIARY ROUTINES**

H01: Monte Carlo History Generator.

A01: Analysis of H01 Histories for Point Detectors.

A02: Region/Volume Detector Analysis.

A03: Analysis of Uncollided Expectation Flux by Region.

S01: Monte Carlo Primary Source Generator.

S02: Monte Carlo Secondary Gamma-Ray Source Generator.

UDAP: Data ProcessorA02 Output to VORSO Input.

ADD: Combiner CodeData Merging for COHORT.

VORSO: Source Data Generator for Volumes of Revolution.

CROS2: Neutron Cross Section (ENDF/B) Data Generator.

SPCT2: Inelastic Neutron Spectrum Probability Tables (ENDF/B) Generator for H01.

SCAT2: Differential Elastic Scattering (ENDF/B) Data Generator.

J01: Multiple Super Group Data Processor.

C01: Edit Code for Source, History, Leakage, or Sorted Data.

The original design of the Monte Carlo codes in this package dates back to work done at General Dynamics, Fort Worth, Texas, in 1962 and development continued in the COHORT series at Radiation Research Associates (RRA), Fort Worth, and Brown Engineering (BE), Huntsville, Alabama, for NASA Marshall Space Flight Center (1964). COHORT was further developed at NASA/Lewis Research Center (CCC-198/COHORT-II, 1972) and also by RRA for Aerojet for ACOH. The BE work resulted in CCC-169/CAVEAT. The ENDF format treated is that of late 1971, early 1972.

**2. CONTRIBUTOR**

Radiation Analysis Group, Aerojet Nuclear Systems Company, Sacramento, California.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; IBM 360/370 (A) or UNIVAC 1108 (B).

**4. NATURE OF PROBLEM SOLVED**

ACOH is part of an integrated system of codes generalized to be applied to many radiation analysis and shielding problems, ranging from simple point source/infinite air scattering to complex 3-dimensional Monte Carlo analyses (CCC-189/ADO, CCC-190/AKERN). The packages are based on modular programming with extensive code coupling with uniform geometry routines (as in CCC-98/FASTER). A typical reactor problem can be started as a discrete ordinates analysis, carried through complicated 3-D configurations with the exactness afforded by the Monte Carlo technique and involve any combination of these two or point kernel analyses at any point in the progression of the solution.

ACOH is a Monte Carlo code system for the solution of neutron and photon transport problems designed to be used in predicting the radiation environment of the NERVA engine, associated space vehicles, and test facilities. The modularized approach with coupling, variable dimensioning, and the common (FASTER) geometry routines add to ACOH's flexibility for application to a wide range of problems.

**5. METHOD OF SOLUTION**

Reliance is placed on the generation of particle history information with specific analysis and reanalysis for information of different types during the execution of the problem, as opposed to a "single" Monte Carlo calculation. Extensive use is made of tagging routines to preserve specialized information for later reuse. Primary data for neutron cross sections are obtained from an evaluated data set such as ENDF/B or from other appropriate sources. The photon cross section data are derived from an evaluation made by Lawrence Radiation Laboratory.

The modularized approach is evident in the list of auxiliary routines (Item 1) and the title indicating the use of each code.

**6. RESTRICTIONS OR LIMITATIONS**

None noted.

**7. TYPICAL RUNNING TIME**

None noted for the IBM 360/370 computer. The packaged sample problem was timed as follows on the UNIVAC 1108: H01-1 1/2 minutes; A01-4 minutes; A02-2 1/2 minutes; A03-1 minute; S01-10 seconds; S02-35 seconds; UDAP-23 seconds; ADD-2 minutes; VORSO-1 minute.

**8. COMPUTER HARDWARE REQUIREMENTS**

ACOH is operable on the IBM 360/65/75/91 or UNIVAC 1108 computers and requires a maximum of 5 storage devices in addition to I-O.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A FORTRAN IV compiler is required.

**10. REFERENCES**

E. A. Warman, D. R. Rogers, and B. A. Lindsey, "NERVA Radiation Analysis Computer Codes CollectionVolume I Summary," ANSC EOR N8140R: 72-0015 (April 1972).

D. G. Lindstrom, "Shielding Code Improvements," ANSC SRT-FRS20-W393al (February 1971).

D. G. Lindstrom and K. O. Koebberling, "Shielding Code Development Program," ANSC RN-S-0541 (February 1970).

J. K. Warkentin, J. H. Price, and M. B. Wells, "User's Manual for COHORT, A Monte Carlo Program for Calculation of Radiation Heating and Transport on the IBM 360," RRA-T7014 (October 1970).

J. H. Price and M. B. Wells, "COHORT with Specular Reflection Surfaces and Albedo Techniques," RRA-T7105 (June 1971).

N. M. Kosko, "Tape-Read Code, C01," ANSC Informal Note P E16810 (June 1969).

J. H. Price and J. K. Warkentin, "Utilization Instructions for CROS2," RRA-N921 (June 1969).

J. K. Warkentin, "Utilization Instructions for VORSO," RRA-N705 (March 1970).

J. Price and K. Warkentin, "Utilization Instructions for SCAT2," RRA-N927 (June 1969).

J. Price and K. Warkentin, "Utilization Instructions for SPCT2," RRA-N923 (June 1969).

J. H. Price and M. B. Wells, "Biasing Techniques in Monte Carlo," RRA-T7014 Appendix A (June 1971).

M. B. Wells and J. D. Marshall, "The Application of Adjoint Biasing to Monte Carlo," RRA-T7014 Appendix B (June 1971).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents and one (1.2MB) DOS diskette which contains the source code and sample problem input.

**12. DATE OF ABSTRACT**

September 1975.

**KEYWORDS:** NEUTRON; GAMMA-RAY; MONTE CARLO; COMPLEX GEOMETRY;
ENDF/B FORMAT