Monte Carlo simulations and data fitting for neutron three-axis spectrometers

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1. Introduction


RESTRAX is a tool for simulating TAS resolution functions and data fitting. The program includes both a high-speed analytical (Gaussian) convolution algorithm and a Monte Carlo ray-tracing code providing enhanced accuracy in description of most of the spectrometer components. The non-linear least-squares fitting routine is available with several scattering function models, which may be used either directly or as templates for other models created by users and called by Restrax as a dynamically linked run-time module. Graphical output permits visualisation of resolution functions in an arbitrary projection in the (Q,ω) space, plotting both simulated and experimental data and mapping S(Q,ω) as 2-dimensional sections in reciprocal space.

Typical tasks where RESTRAX may help:
Planning an experiment
RESTRAX permits to find optimum instrument configuration with respect to required size and orientation of the resolution function.
Simulating data for a given scattering model
Smearing due to instrumental resolution and relative intensities of diverse signal components can be assessed by simulation of experimental data with an expected scattering law.
Analysis of experimental data
The data fitting with RESTRAX is particularly useful in two cases: (1) when the Gaussian approximation of the resolution function is not sufficient and/or (2) when a complex scattering model is needed, which cannot be expressed as a simple analytical formula. With RESTRAX, you can also simultaneously fit multiple datasets with a single set of model parameters.

Note: This page does not refer to another modification of RESTRAX called SIMRES - an enhanced ray-tracing code useful for simulation of newly designed or upgraded instruments and optimisation of their configuration. Please consult the home page for more information and downloads.