**1. NAME AND TITLE**

CAVEAT: General Purpose Monte Carlo Time-Dependent Radiation Transport Code in Complex Geometry.

**AUXILIARY ROUTINES**

CSIR-ENDF/B: Tape Handling Cross Section Library Code.

LEGWORK: Average Differential Elastic Scattering Distribution Generator.

CAVEAT is based on an early version of COHORT developed by Radiation Research Associates (RRA) for NASA/MSFC. See also CCC-198/COHORT II, contributed by NASA/LRC, based on the same original source.

**2. CONTRIBUTORS**

Teledyne Brown Engineering and NASA George C. Marshall Space Flight Center, Huntsville, Alabama.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV and Assembler language; IBM 360.

**4. NATURE OF PROBLEM SOLVED**

CAVEAT is a general purpose Monte Carlo code system which treats the transport of neutrons, gamma rays, and secondary gamma rays in evaluating radiation shielding requirements. Its routines solve the general quadratic surface equations with the additional features of time dependence, exponential density completion of a shielding problem from source generation to analysis of fluence and/or dose in a series of job steps for third generation computers.

**5. METHOD OF SOLUTION**

CAVEAT employs the logic of random walk processes in the Monte Carlo numerical techniques for solving radiation shielding problems in complex geometry. Isotropic inelastic and anisotropic elastic scatterings are treated. Exponential transformation and Russian roulette procedures are available as importance sampling techniques.

One method of analysis in CAVEAT calculates the fluence and/or dose collided and uncollided contribution at point detectors as a function of time, energy, polar angle, and azimuthal angle. Analysis may also be done by using estimates of the average track length within each geometric region. Source parameter descriptions are selected for energy, angle, spatial coordinates, time and weight from either fixed or discrete probability tables. Secondary gamma-ray generation is accounted for.

A stepwise typical procedure for a CAVEAT shielding problem may be:

S01 Neutron source particle generation

H01 Transport of neutron source particles

A01 Analysis of neutron response

S02 Secondary gamma generation

H01 Transport of secondary gamma particles

A01 Analysis of gamma response.

**6. RESTRICTIONS OR LIMITATIONS**

As a result of the variable dimensioning technique, a judicious tradeoff with data parameters between detailed geometry description, point cross section table values, and other library data for anisotropic scattering and inelastic scattering data needs to be exercised by the user. A restriction on computer execution time may be above average for similar problems performed by CAVEAT rather than by another Monte Carlo program. CAVEAT has no capability for performing the adjoint method of solution in a radiation shielding problem.

**7. TYPICAL RUNNING TIME**

The sample problem used the following on an IBM 360/91 computer:

Code S01: 18 sec CPU time, 124K bytes for the GO step, and 2 tapes/direct access devices in addition to I-O.

Code H01: 1.64 min CPU time, 188K bytes for the GO step, and 5 tapes/direct access devices in addition to I-O.

Code A01: 3 min CPU time, 182K bytes for the GO step, and 4 tapes/direct access devices in addition to I-O.

**8. COMPUTER HARDWARE REQUIREMENTS**

CAVEAT is operable on an IBM 360/75/91 computer with a maximum of 5 tapes or direct access devices in addition to I-O. With variable dimensioning, the program storage size is limited only by computer storage capability and the proper alteration to the blank COMMON statements in CAVEAT. The clock is sampled in the random walk procedure.

**9. COMPUTER SOFTWARE REQUIRMENTS**

A FORTRAN IV compiler and an OS-360 operating system are required. OVERLAY is used. Three special routines (Random Number Generator, IDAY, and TIME) are used and are included in the code package.

**10. REFERENCES**

**a. Included in the documentation: **

N. R. Byrn, "CAVEAT: A Revised Version of the General Purpose Monte Carlo Program COHORT," Technical Note SE-290. Vol 1--Theory and Techniques (October 1969). Vol 2--User's Manual (August 1969).

**b. Background information:**

H. T. Smith, "Preliminary Results of CAVEAT Verification on Benchmark Problems," SMD-SSL-1130 (April 1970).

A. E. Profio, ed., "Shielding Benchmark Problems," ORNL-RSIC-25 (1969).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document (10.a) and one (1.2MB) DOS diskette which contains the source code and sample problem input and output.

**12. DATE OF ABSTRACT**

September 1972; revised April 1975.

**KEYWORDS: ** MONTE CARLO; NEUTRON; GAMMA-RAY; COMPLEX GEOMETRY;
TIME DEPENDENT