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[Program Service | Recent programs]

NEA-0643 DISCUS. (Abstract last modified 10-FEB-1993)


DISCUS, Neutron Single to Double Scattering Ratio in Inelastic Scattering Experiment by Monte-Carlo

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Abstract Table of Contents:

NAME | COMPUTER | PROBLEM | SOLUTION | RESTRICTIONS | CPU | FEATURES | AUXILIARIES | STATUS | REFERENCES | REQUIREMENTS | LANGUAGE | OPERATING SYSTEM | OTHER RESTRICTIONS | AUTHOR | MATERIAL | CATEGORIES |

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1. NAME OR DESIGNATION OF PROGRAM - DISCUS: A computer program for the calculation of multiple scattering effects in inelastic neutron scattering experiments.


2. COMPUTER FOR WHICH PROGRAM IS DESIGNED AND OTHER MACHINE VERSION PACKAGES AVAILABLE -

To request or retrieve programs click on the one of the active versions below. A password and special authorization is required.

Explanation of the status codes.

Program-name         Package-ID  Status
DISCUS               NEA-0643/01 Report

Machines used:
Package-ID     Orig.Computer                       Test Computer
NEA-0643/01                                        

3. DESCRIPTION OF PROBLEM OR FUNCTION - DISCUS calculates the ratio of once-scattered to twice-scattered neutrons detected in an inelastic neutron scattering experiment. DISCUS also calculates the flux of once-scattered neutrons that would have been observed if there were no absorption in the sample and if, once scattered, the neutron would emerge without further re-scattering or absorption. Three types of sample geometry are used: an infinite flat plate, a finite flat plate or a finite length cylinder. (The infinite flat plate is included for comparison with other multiple scattering programs.) The program may be used for any sample for which the scattering law is of the form S(/Q/, omega).


4. METHOD OF SOLUTION - Monte Carlo with importance sampling is used. 
Neutrons are "forced" both into useful angular trajectories, and useful energy bins. Biasing of the collision point according to the point of entry of the neutron into the sample is also utilised. The first and second order scattered neutron fluxes are calculated in independent histories. For twice-scattered neutron histories a square distribution in Q-omega space is used to sample the neutron coming from the first scattering event, whilst biasing is used for the second scattering event. (A square distribution is used so as to obtain reasonable inelastic-inelastic statistics.)


5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM - Unlimited number of detectors. Max. size of (Q, omega) matrix is 39*149. Max. number of points in momentum space for the scattering cross section is 199.


6. TYPICAL RUNNING TIME - Typically 0.42 secs. per energy bin per 1,000 neutron histories on the Harwell IBM 370/165.


7. UNUSUAL FEATURES OF THE PROGRAM - An essential feature of the code is its calculation speed due to consideration of only single and double scattering effects, and sophisticated importance sampling.


8. RELATED AND AUXILIARY PROGRAMS - A comparable program is the Monte Carlo code 'MSC' which included up to 10th order scattering effects.


9. STATUS
NEA-0643/01: 10-FEB-1993 Report Only


10. REFERENCES  - 
- M.W. Johnson: 
  "DISCUS - A Computer Program for the Calculation of Multiple 
  Scattering Effects in Inelastic Neutron Scattering Experiments" 
  AERE-R7682 (1974). 
- F.G. Bischoff et al.: 
  (MSC) 
  Nucl. Sci. Eng. 48, 266 (1972). 
NEA-0643/01:


11. MACHINE REQUIREMENTS - 120 K bytes of core storage are required by the program. 


12. PROGRAMMING LANGUAGE(S) USED -
NEA-0643/01: 


13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED - 


14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS - In ad- dition to the four subroutines in DISCUS, the user must supply the following subroutines which are required in connection with the gen- eration of the pseudorandom number sequence. (These are all stan- dard HARWELL Subroutine Library Programs.):
REAL FUNCTION FAO1AS (I) 
The function value returned by FAO1AS is a real pseudorandom number in the range (0.0 to 1.0) if I is positive or zero; or in the range (-1.00 to 1.00) if I is negative.
SUBROUTINE FAO1BS (MAX, NVALUE) 
This subroutine will set NVALUE to a pseudorandom integer in the interval (1 to MAX) inclusive. MAX should always be positive otherwise there will be a bias towards zero.
SUBROUTINE FAO1DS (I,J) 
Resets the value of the generator words used in FAO1AS or FAO1BS according to the input values of I,J. J must always be odd if one uses the Harwell subroutine library programs.
SUBROUTINE FAO1CS (I,J) 
Passes back the current contents of the generator words via the variables I,J.


15. NAME AND ESTABLISHMENT OF AUTHOR - 
          M. W. Johnson 
          Materials Physics Division 
          AERE Harwell 
          Oxfordshire, United Kingdom. 


16. MATERIAL AVAILABLE -
NEA-0643/01:
report                                                              REPPT


17. CATEGORIES  - 

- O.  Experimental Data Processing


Keywords: INELASTIC SCATTERING, MONTE CARLO METHOD, NEUTRON FLUX

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