**1. NAME AND TITLE**

CYGNUS-C SPHERE: Monte Carlo Neutron Transport Code System in Spherical Geometry.

**2. CONTRIBUTOR**

Department of Engineering, Kyoto University, Japan.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; IBM 360/370.

**4. NATURE OF PROBLEM SOLVED**

CYGNUS-C SPHERE uses the Monte Carlo method for calculating the neutron energy-angular
distribution in an homogeneous sphere at the center of which there is a volume neutron source.
The monoenergetic or energy-distributed neutrons are assumed to be uniformly distributed in the
source and to be isotropically emitted from the source.

**5. METHOD OF SOLUTION**

CYGNUS-C SPHERE solves neutron transport problems in a spherical medium by the collision
density Monte Carlo method. the Coveyou technique was adopted for selecting neutron elastic
scattering angles.

**6. RESTRICTIONS OR LIMITATIONS**

The thermal neutron cannot be treated with this code system. The energy range to be
calculated is equal to that of the cross section data. The energy mesh points of the cross section
data are within 410 points. This code is presently limited to 5 elements in one medium.

**7. TYPICAL RUNNING TIME**

About 12 minutes are required in 20,000 histories for a graphite of 80-cm radius and the
energy cutoff of 500 keV.

**8. COMPUTER HARDWARE REQUIREMENTS**

CYGNUS-C SPHERE is operable on the IBM 360/370 computers. It uses 52 K of storage.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A FORTRAN IV compiler is required.

**10. REFERENCES**

H. Hirayama and T. Nakamura, "Monte Carlo Calculation of Neutrons Transmitted through
Matter," *Memoirs of the Faculty of Engineering, Kyoto University, Vol. XXXIV, Part 2*, 187-204
(April 1972).

T. Nakamura, H. Hirayama, S. Nishino and T. Hyodo, "Spacial Distribution of Photoneutrons
in an Iron Slab Produced by 20-MeV Electron Bombardment," *Memoirs of the Faculty of Engineering, Kyoto University, Vol. XXXVI, Part 1*, 60-69 (January 1974).

E. J. McGrath and D. C. Irving, "Techniques for Efficient Monte Carlo Simulation: Vol
IIRandom Number Generation for Selected Probability DistributionsAppendix B, MIRANA
Machine Independent Package for Generating Uniform Random Numbers," ORNL-RSIC-38, Vol
II (SAI-72-590-LJ) (April 1975).

**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 and output.

**12. DATE OF ABSTRACT**

July 1975; revised October 1982.

**KEYWORDS: ** NEUTRON; MONTE CARLO; SPHERICAL GEOMETRY