**1. NAME AND TITLE**

ANTE 2: Adjoint Monte Carlo Time-Dependent Neutron Transport Code in Combinatorial Geometry.

AUXILIARY ROUTINE

PAT: Neutron Element Data Tape Generator (from ENDF Format.)

ADCROS: Adjoint Data Generator.

MAS: Monte Carlo Calculation.

Two versions are packaged: ANTE 2 for the CDC 6600 (A) and ANTE-BELLM for the IBM 360 (B).

**2. CONTRIBUTORS**

Mathematical Applications Group, Inc. (MAGI), White Plains, New York.

Bell Telephone Laboratories, Whippany, New Jersey.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; CDC 6600 (A) OR IBM 360/75/91 (B).

**4. NATURE OF PROBLEM SOLVED**

Given a finite neutron transmitting medium (hereafter called the object or transmission object) and given a neutron detector embedded in that medium, what would be the response of the detector to an arbitrary neutron flux field in which the object is immersed? ANTE 2 computes an importance weighting function over a surface which contains the object. Thus any arbitrary flux field may be weighted by this function to determine the effect this field would produce upon the enclosed detector.

**5. METHOD OF SOLUTION**

Whereas conventional neutron Monte Carlo programs seek to generate flux distributions (which may be called the contravariant aspect) from specified sources and are usable in estimating effects upon arbitrary (within practical limits) detectors, this program deals with the covariant aspect and seeks to generate importance or adjoint distributions for definite detectors usable in estimating effects from arbitrary (within practical limits) sources.

There appear to be four principal features of the program.

1. Geometry. The following objects are building blocks of the geometry: sphere, right elliptical cylinder, truncated right angle cone, ellipsoid, or convex polyhedron of 4, 5, or 6 sides. These building blocks may be combined in arbitrary fashion--unions or intersections. An elegant Boolean notation is used to describe the combinations.

2. Scattering kernels. Differential cross-section data must be analyzed to construct probability distributions of the phase coordinates of a particle prior to a collision which produces some definite exit phase coordinates. This data preparation may be viewed as the heart of the calculation and may be usefully adapted to other Monte Carlo calculations of adjoints.

3. Standard Monte Carlo techniques are used in particle tracking and construction of histories.

4. Scoring. The transmission object is considered to be completely enclosed by a scoring surface which must be a rectangular parallelepiped or a sphere. Scoring bins represent meshes of time, energy, polar, and azimuthal angles. The surfaces of the rectangular parallelepiped may be further subdivided to provide spatial binds. In the case of spherical enclosure, no provision is made for surface subdivision or for recording azimuthal angles of escape. Hence, only spherically symmetric problems can be addressed with this option.

Included in the package are the following routines: PAT abstracts required cross section data from ENDF/B files; ADCROS receives cross-section data from PAT, operates on it to provide scattering kernels and other basic data required for adjoint calculation and makes an ADCROS tape; CPROC processes geometric description provided in input and places results on ADCROS tape; and MAS performs the calculation after the above preparations are made.

**6. RESTRICTIONS OR LIMITATIONS**

None noted.

**7. TYPICAL RUNNING TIME**

Estimated running time for the sample problem on the IBM 360/75: PAT, 1 minute; ADCROS, 5 minutes; and MAS, 7 seconds.

**8. COMPUTER HARDWARE REQUIREMENTS**

The codes are operable on the CDC 6600 or the IBM 360/75/91 computers with standard I/O, and a maximum of 9 tape units or direct access devices. Approximately 400K is required in the GO step.

**9. COMPUTER SOFTWARE REQUIREMENTS**

ANTE 2 was designed for the FORTRAN IV CDC 6600 Operating System. It is also operable on the IBM 360/75/91 Operating System using an OS 360 FORTRAN H compiler.

**10. REFERENCES**

**a) Included in documentation:**

O. Cohen, "ANTE 2A FORTRAN Computer Code for the Solution of the Adjoint Neutron Transport Equation by the Monte Carlo Technique," DASA-2396 (January 1970).

O. Cohen and W. Guber, "ANTE-BELLMA Computer Program for the Solution of the Adjoint Neutron Time Dependent Transport Equation by the Monte Carlo Technique," MR-7003

(March 1970).

**b) Background Information:**

W. Guber, "The Combinatorial Geometry Technique for the Description and Computer Processing of Complex Three-Dimensional Objects," MR-7004/2 (March 1970).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents and one (1.2MB) DOS diskette which contains the source codes and sample problem input. A library of cross sections (ENDF/B-Version I) for use in the sample problem is included in the package.

**12. DATE OF ABSTRACT**

August 1971; revised July 1982, February 1985.

**KEYWORDS:** ADJOINT; MONTE CARLO; TIME-DEPENDENT; NEUTRON; COMBINATORIAL GEOMETRY