NEA-0643 DISCUS.
DISCUS, Neutron Single to Double Scattering Ratio in Inelastic Scattering Experiment by Monte-Carlo
NAME OR DESIGNATION OF PROGRAM, COMPUTER, DESCRIPTION OF PROBLEM OR FUNCTION, METHOD OF SOLUTION, RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM, TYPICAL RUNNING TIME, UNUSUAL FEATURES OF THE PROGRAM, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED, OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES
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| Program name | Package id | Status | Status date |
|---|---|---|---|
| DISCUS | NEA-0643/01 | Report | 10-FEB-1993 |
Machines used:
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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).
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).
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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.)
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.)
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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.
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.
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Keywords: Monte Carlo method, inelastic scattering, neutron flux.