[ Identification | Description | Input parameters | Output parameters | Links ]

# The `ILL_D1A` Instrument

Simple monochromator Diffractometer for powders (D1A), with container/sample environment and radial collimator. May simulate a silica phase transition experiment.

## Identification

- Site: ILL
- Author: E. Farhi
- Origin: LLB/ILL
- Date: 13 Apr 2006
- Version: 1.3

## Description

    D1A is a reliable diffractometer for standard crystallographic problems. It gives
    excellent results with the Rietveld method owing to its near perfect Gaussian
    peak-shape in the 2θ-range 30° to 150°.

    Special features include
      a high fixed take-off angle of 122 deg, giving high resolution at large
        scattering angles (up to 160 deg);
      a bank of 25 high efficiency collimators and counters;
        an anisotropically squashed germanium monochromator focussing a 250
        mm high beam onto only 30 mm;
      a wide choice of wavelengths, from 1.39 Angs to 2.99 Angs, quickly available by
        simple rotation of the focussing monochromator;

    The large monochromator take-off angle means that the diffraction pattern is
    focussed for the parallel geometry shown (2θ = 122°). The counter can be swept
    through 0 deg to 2θ = 160° deg for the highest angle counter, usually in steps
    of 0.05 deg.
    Monochromator           Neutron wavelength
    Ge 117 DM=0.7946 AA     1.390
    Ge 335 DM=0.8655 AA     1.514
    Ge 115 DM=1.0925 AA     1.911 (optimal)
    Ge 113 DM=1.712 AA      2.994

    The sample is a powder or a liquid, in a container can, all positioned in an
    Al environment (e.g. cryostat/furnace shield).
    This instrument model does not include the guide. For the 'SiO2' sample, one may
    change the Temperature to simulate a phase transition (for teaching purposes):
       T[C]        573          1650
       quartz alpha < quartz beta < melt silica

    Example: mcrun D1A.instr lambda=1.911
             mcrun D1A.instr -N 10 lambda=1.911 Powder="SiO2" Temperature=300,2000

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default
--- | --- | --- | ---
lambda | Angs | Wavelength at monochromator | 1.911
DM | Angs | d-spacing of monochromator. Use DM=0 to compute the values from the requested wavelength. | 0
powder | extension .qSq | [str] File name for powder description, or S(q) file | "SiO2"
Temperature | K | Sample temperature, to study phase changes. Only applies when Powder is set to SiO2. | 300

## Links

- Source code for `ILL_D1A.instr`.

[ Identification | Description | Input parameters | Output parameters | Links ]