1. NAME AND TITLE

DIFBAS: A Bayesian Approach to Unfolding a Neutron Spectrum From a Spectrum of Recoiled Protons.

AUXILIARY ROUTINES: CUPR, FOC, GOALRE, MB, RMC, SPHC, TRANSMAT, TRANSPHS

2. CONTRIBUTOR

Physikalisch-Technische Bundesanstalt, Braunschweig, Germany and Institute of Radiation Dosimetry, Czech Republic.

3. CODING LANGUAGE AND COMPUTER

FORTRAN-77; VAX and IBM PC (P00334/MNYCP/00).

4. NATURE OF PROBLEM SOLVED

DIFBAS is used to unfold pulse height spectra measured by a proton recoil detector (e.g. H2 filled proportional counters or organic scintillators) to obtain neutron spectra. It can be used generally for the unfolding of arbitrary many channel spectra containing original particle spectra folded by a detector response (e.g. spectra of photon detectors).

5. METHOD OF SOLUTION

The algorithm is based on the Bayesian conditional probability assuming normal distributions of both the pulse height and the a priori spectra. The covariance filter method is employed to calculate the a posteriori spectrum and covariance matrix of the neutron spectrum.

6. RESTRICTIONS OR LIMITATIONS

Uncertainties of the response matrix are not taken into account. This is due to their unavailability and to the intention of keeping the computer requirements of the code in the range of a PC.

The SPHC utility reads unformatted files written by SPEKT (G. Dietze, "A Dialog Program for Multichannel Spectra Analysis", PTB-ND-13, June 1978). SPEKT is not included in the PSR-334 package and is not available at RSIC.

The MB and RMC codes are interdependent and read formatted files written by NRESP7 (G. Dietze, H. Klein, "NRESP4 and NEFF4 Monte Carlo Codes for the Calculation of Neutron Response Functions and Detection Efficiencies for NE 213 Scintillation Detectors" PTB-ND-22, 1982). NRESP7 is not included in the PSR-334 package and is not available at RSIC.

7. TYPICAL RUNNING TIME

DIFBAS (PC) - 37 seconds (with SMARTDRV)

DIFBAS (VAX) - 2 minutes 23 seconds (average)

8. COMPUTER HARDWARE REQUIREMENTS

PC Version: A desktop machine based on an INTEL or comparable processor with at least 500K of available RAM.

VAX Version: A DEC VAX computer.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran 77 compiler is required. The code system was tested by RSIC on a VAX 6000-420 running VMS 5.5 using the Fortran compiler, version 5.9 and on a Northgate 486/66 running MS-DOS 6.0 using MS Fortran 5.0.

10. REFERENCE

M. Tichy, "The DIFBAS Program - Description and User's Guide," PTB-7.2-93-1 (April 1993).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one DS/HD 5.25" (1.2 MB) diskette in DOS compressed format containing the PC and VAX source codes, utilities, and data files.

12. DATE OF ABSTRACT

August 1993.