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

The ILL_D1A Instrument

Identification

Description

Input parameters

Links

The `ILL_D1A` Instrument