[ Identification | Description | Input parameters | Links ]

The Test_Monitor_Sqw Instrument

A simple ToF with cylindrical/spherical sample, and furnace/cryostat/container. The sample can be hollow.

Identification

• Site: Tests_samples
• Author: E. Farhi
• Origin: ILL
• Date: Feb 2014

Description

This instrument models a generic, tunable, neutron time-of-flight spectrometer.

The incoming flux at the sample brings neutrons with 'beam_wavelength_Angs' wavelength.
The energy resolution at the sample is given as 'beam_resolution_meV'.
The beam size at the sample is set to the sample cross section (e.g. ~2 x 5 cm).

The sample geometry is either cylindrical ('sample_radius_m' and 'sample_height_m')
or spherical ('sample_height_m=0'). The sample can be hollow when given a thickness
'sample_thickness_m', or filled ('sample_thickness_m=0'). When in cylindrical geometry,
it is surrounded by a container with thickness 'container_thickness_m'. The container
material is specified as a powder file name 'container' in the McStas Sqw or PowderN format,
e.g. 'Al.laz' or 'Nb.laz'. Setting 'container=0' removes the container.

The sample scattering is characterised by its coherent and incoherent contributions
given as 'sample_coh' and 'sample_inc' file names in McStas Sqw or PowderN format.
Setting the 'sample_coh=sample_inc=0' removes the sample, e.g. to study the container or
environment only contribution.

The sample and its container are located inside a cylindrical shield with radius
'environment_radius_m' and thickness 'environment_thickness_m'. The material is set from
the 'environment' file name in the McStas Sqw or PowderN format (e.g. 'Al.laz').
This way, it is possible to estimate the contribution of a cryostat or furnace.
Setting 'environment=0' removes the environment.

The detector has a cylindrical geometry, with a radius 'sample_detector_distance_m'
and tubes with height 'detector_height_m'. The detector covers a -30 to 140 deg angular range
with 2.54 cm diameter tubes (the number of tubes is computed from the distance).
The direct beam (non scattered neutrons) is discarded.

The detector produces both (angle,tof) and (q,w) data sets, for:
total scattering
coherent single scattering from sample
incoherent single scattering from sample
multiple scattering from sample
scattering from the container and sample environment
The (angle,tof) results are corrected for the parallax effect from the detector height.

Known configurations:
ILL_IN4:
beam_wavelength_Angs=2, beam_resolution_meV=0.5,
sample_detector_distance_m=2.0, detector_height_m=0.3
ILL_IN5:
beam_wavelength_Angs=5, beam_resolution_meV=0.1,
sample_detector_distance_m=4.0, detector_height_m=3.0
ILL_IN6:
beam_wavelength_Angs=4.1, beam_resolution_meV=0.1,
sample_detector_distance_m=2.48, detector_height_m=1.2
PSI_Focus:
beam_wavelength_Angs=4.1, beam_resolution_meV=0.1,
sample_detector_distance_m=2.5, detector_height_m=1.2
FRM2_TOFTOF:
beam_wavelength_Angs=3.0, beam_resolution_meV=0.3,
sample_detector_distance_m=4.0, detector_height_m=2.0
SNS_SEQUOIA:
beam_wavelength_Angs=1.0, beam_resolution_meV=3.0,
sample_detector_distance_m=5.5, detector_height_m=1.2
SNS_ARCS:
beam_wavelength_Angs=0.3, beam_resolution_meV=20.0,
sample_detector_distance_m=3.0, detector_height_m=1.46
NIST_DCS:
beam_wavelength_Angs=3.0, beam_resolution_meV=0.2,
sample_detector_distance_m=4.0, detector_height_m=1.2
ISIS_MERLIN:
beam_wavelength_Angs=1.0, beam_resolution_meV=2.4,
sample_detector_distance_m=2.5, detector_height_m=3.0
ISIS_LET:
beam_wavelength_Angs=4.0, beam_resolution_meV=0.1,
sample_detector_distance_m=3.5, detector_height_m=4.0

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
beam_wavelength_Angs	Angs	incident neutron beam wavelength	2
beam_resolution_meV	meV	incident energy range full width	0.1
sample_coh	str	sample coherent Sqw data file or NULL	"Rb_liq_coh.sqw"
sample_inc	str	sample incoherent Sqw data file or NULL	"Rb_liq_inc.sqw"
sample_thickness_m	m	thickness of sample. 0=filled	1e-3
sample_height_m	m	height of sample. 0=sphere	0.03
sample_radius_m	m	radius of sample (outer)	0.005
container	str	container material or NULL	"Al.laz"
container_thickness_m	m	container thickness	50e-6
environment	str	sample environment material or NULL	"Al.laz"
environment_radius_m	m	sample environment outer radius	0.025
environment_thickness_m	m	sample environment thickness	2e-3
detector_height_m	m	detector tubes height	3
sample_detector_distance_m	m	distance from sample to detector	4.0

Links

• Source code for Test_Monitor_Sqw.instr.
• The Isotropic_Sqw sample
• The PowderN sample
• The Samples_Isotropic_Sqw example instrument
• The nMoldyn package to create Sqw data sets from MD trajectories

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[ Identification | Description | Input parameters | Links ]

Generated on 2024-01-03 11:47:43

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Last Modified: Tuesday, 16-Apr-2024 20:05:21 CEST