**1. NAME AND TITLE**

PIXSE: A Generator of Multigroup and Multipoint Cross Sections for Thermal Reactor
Calculations.

**2. CONTRIBUTOR**

United Kingdom Atomic Energy Authority, Winfrith, Dorchester, Dorset, England, through the
OECD NEA Data Bank, Gif-sur-Yvette, France.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV; IBM 360/370.

**4. NATURE OF PROBLEM SOLVED**

PIXSE computes, from the scattering law, generalized energy transfer cross-section matrices and source terms for thermal reactor calculations. Either group or point cross sections may be obtained so that data may be obtained from PIXSE for both multigroup and multipoint calculations.

Energy transfer calculations may be performed for any scattering law; the free gas and ``effective
width'' models are built into the program, and a tabulation of S(alpha,beta) of any other law may be
used as input data.

**5. METHOD OF SOLUTION**

The integrals are evaluated by Gaussian quadrature; the constants for a 3, 5 or 7 pint Gaussian are included in PIXSE, and other n-point Gaussian for n between 3 and 19 may be used if the Gauss ordinates and weights are specified as data. The differential scattering cross section is computed from the scattering surface and the particular values required in evaluating the integral are found by liner interpolation.

PIXSE can calculate either a scattering matrix of point values for values of the energy as specified
by the input data or group averaged values of the cross section weighted by a spectrum function.

**6. RESTRICTIONS OR LIMITATIONS**

None noted.

**7. TYPICAL RUNNING TIME**

Running times for PIXSE depend somewhat on the problem being solved. A 40-group gas
calculation appears to take about 2 min but may take somewhat longer for H or D where the source
calculation occupies a relatively large amount of the computing. 40-group calculations from a
tabulation of S(alpha,beta) have taken between 4 and 20 minutes; the difference is probably due to the
length of time required to carry out the table search.

**8. COMPUTER HARDWARE REQUIREMENTS**

PIXSE is operable on the IBM 360/370 computers.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran IV compiler is required.

**10. REFERENCE**

J. D. MacDougall, "PIXSE," AEEW-M 318 (April 1963).

**11. CONTENTS OF CODE PACKAGE**

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

**12. DATE OF ABSTRACT**

March 1984.

**KEYWORDS: ** MULTIGROUP CROSS SECTION PROCESSING; NEUTRON CROSS
SECTION PROCESSING