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Manuscript Title: Slit height smearing correction in small angle X-ray scattering I: intensity correction program.
Authors: M. Deutsch
Program title: CORECTEX
Catalogue identifier: AASB_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 17(1979)337
Programming language: Fortran.
Computer: IBM 370/168.
Operating system: OS/VS2.
RAM: 47K words
Word size: 32
Keywords: Crystallography, X-ray, Scattering, Diffraction, Smearing, Slit.
Classification: 8.

Subprograms used:
Cat Id Title Reference
AASC_v1_0 FFITEX CPC 17(1979)345

Revision history:
Type Tit le Reference
adaptation 0001 CORECTSP See below

Nature of problem:
The use of pinhole collimators in small angle X-ray scattering is impractical due to the low intensity obtained at the detector. Instead, long narrow slits, or their equivalents are used to collimate the beam. Consequently the measured intensity is an integral of the intensity scattered through a range of angles rather than the intensity scattered at the nominal measured angle. This effect is known as the slit-height smearing effect. To obtain the ideal intensity scattered at a unique angle, as if pinhole collimation was feasible, the data must be corrected for this effect. The present program is an implementation of our exact solution to this problem. It yields highly accurate results.

Solution method:
Each corrected intensity value is obtained by integrating an expression involving the measured data and a correction function g(t). This function is the solution of an integral equation involving the slit transmission function f(t). A method was developed for solving this equation exactly using Laplace transform techniques. Prior to using this program, the following preparatory procedure is required. First, the transmission function f(t) of the apparatus to be used in the experiment must be measured. Then, an appropriate form of f(t) is chosen and fitted to the data using another program (AASC). The parameters obtained in the fit automatically define the g-function to be used for correcting the scattering intensity data measured with the same apparatus. These parameters and the measured intensity values serve as input to the present program. Note that the data fitting procedure need be performed only once for a given apparatus.

Restrictions:
Only 250 intensity values can be corrected by the present version in a single run.

Running time:
About 50 s for 250 intensity values.

ADAPTATION SUMMARY
Manuscript Title: Slit height smearing correction in small angle X-ray scattering III: intensity correction program adaptation to arbitrary slit transmission function.
Authors: M. Deutsch
Program title: 0001 CORECTSP
Catalogue identifier: AASB_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 18(1979)143
Programming language: Fortran.
Classification: 8.

Subprograms used:
Cat Id Title Reference
AASD_v1_0 GTSPLINE CPC 18(1979)149

Nature of problem:
Two previous papers in this series described an implementation of the author's exact solution of the slit height smearing correction problem encountered in small angle X-ray and neutron scattering experiments. That implementation presumed, however, that an analytic form could be found which closely fitted the actual slit transmission function used in the experiment. The adapted program can be used with any slit function and is especially useful in cases where no suitable analytic form for the slit function is available. The program yields highly accurate results, and running time is less than half that of the original program.

Solution method:
The Method described in C.P.C.(17(1979)337). The only differnce is that the measured values of the slit transmission function are now fitted by a piecewise continuous cubic spline function, rather than by an analytic function. The fitting and parameter calculations are done by a separate program which must be run prior to using this program. The input section of the original program and the subroutine calculating the correction function derivative were altered to accommodate the new correction function.

Restrictions:
As in the original program, only 250 intensity values can be corrected in a single run.