**1. NAME AND TITLE**

GADJET: Monte Carlo Gamma-Ray Adjoint Energy Transport Code in Complex Three-Dimensional Geometry.

**AUXILIARY ROUTINE**

EZGEOM: Geometry Input Data Processor.

This code package is retained in RSIC to preserve technology developed in civil defense programs in the 1960s. It was initially developed by the first two contributors below and was later (1971) substantially revised at Kansas State University.

**2. CONTRIBUTORS**

Radioptics, Inc., Plainview, New York.

U. S. Naval Radiological Defense Laboratory, San Francisco, California.

Office of Civil Defense, Washington, D. C.

Kansas State University, Manhattan, Kansas.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV: CDC 6600.

**4. NATURE OF PROBLEM SOLVED**

The code is designed to calculate the effectiveness of structures (of arbitrary complexity) in shielding against fallout fields (finite or infinite), and to calculate the relative importance of each fallout region in contributing to the exposure rate in the structure. Complex realistic structures can be assumed, with windows, sills, black surfaces, etc., being allowed.

**5. METHOD OF SOLUTION**

The code solves the adjoint transport equation for the so-called "importance" function. A knowledge of the importance function, coupled with the source distribution, solves the problem of determining the response of an arbitrary gamma-ray detector located in a structure that is exposed to fallout gamma-ray sources.

GADJET handles the transport of photon energy through matter having a three-dimensional geometry composed of rectangular parallelepipeds which, in turn, may contain spheres, cylinders, parallelepipeds, or wedges.

The source is assumed to be composed of isotropic, monoenergetic gamma-ray emitters distributed uniformly on non-overlapping planes parallel to the air-ground interface. The detector can be either a point or a cylindrical volume detector. It is assumed that the gamma radiation is scattered (Compton scattering) by air, ground, and structure with the photoelectric effect included in the absorbing term. Pair production is excluded. The ground or air can be replaced by air or ground or structure. The structure is composed of a finite number of walls, floors, and roofs, which can be above or below the ground level. They can be made of any material (including perfect gamma absorbers). Apertures such as windows can be included.

EZGEOM takes a simplified geometrical description of the physical system, as provided by the problem originator, and produces a rather complex set of data required by the transport program.

The original GADJET code was written to utilize a hypothetical point detector, which is an adequate approximation for large structures. To make the code more versatile, the code was modified to handle a volume detector as well as a point detector. The volume-detector routine was written so it would pick a starting point inside a cylindrical detector with equal probability per unit volume. The cylindrical detector is placed in the structure so its axis is parallel to the z-axis of the structure which is perpendicular to the plane of contamination.

**6. RESTRICTIONS OR LIMITATIONS**

Some dimensional limitations are as follows:

Maximum number of regions (ordinary and nonordinary): 200

Maximum number of nonordinary regions: 127

Maximum number of distinct nuclides: 33

Maximum number of compositions: 20

Maximum number of nuclides for any composition: 5

Maximum number of energies: 100

**7. TYPICAL RUNNING TIME**

No studies of typical running time have been made by RSIC.

**8. COMPUTER HARDWARE REQUIREMENTS**

The code is designed to run on the CDC 6600 and requires 157,000 bytes of storage space for execution.

**9. COMPUTER SOFTWARE REQUIREMENTS**

The code is operable on FORTRAN IV systems.

**10. REFERENCES**

**a. Included in package:**

F. A. Verser, Kansas State University, Informal Notes on EZGEOM (1971).

S. Presier, M. Kalos, A. Stathoplos, J. G. Beckerley, E. R. Friedman, G. Rabinowitz, H. Sadowski, L. A. Willis, "Calculation of Gamma Exposure Rates in an Open or Covered Basement in Fallout Fields Using the GADJET Code," NRDL-TRC-68-25 (1968).

E. R. Friedman, M. H. Kalos, S. Presier, G. Rabinowitz, J. G. Beckerley, "The Numerical Solution of the Adjoint Transport Equation for Gamma Rays by the GADJET Code," NRDL-TRC-68-27 (1968).

**b. Background information:**

B. Eisenman, F. Nakache, "UNC-SAM, A FORTRAN Monte Carlo System for Calculation of Neutron or Gamma-Ray Transport in Three-Dimensional Geometry," United Nuclear Corporation, Report UNC-5093 (1964).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents (10.a), and one (1.2MB) DOS diskette which contains a cross-section data library, the source codes and input and output for a sample problem.

**12. DATE OF ABSTRACT**

May 1969; updated July 1981; revised September 1991.

**KEYWORDS: ** CIVIL DEFENSE; MONTE CARLO; GAMMA-RAY; COMPLEX GEOMETRY; ADJOINT