IMAT: Imaging and Materials instrument

Technical information and expected performance parameters of IMAT

Technical Summary

IMAT will be placed on a broad-pulse, coupled liquid hydrogen/solid methane moderator on the ISIS TS-2 source which is operated at 10 Hz, in order to achieve a high cold neutron flux for radiography, tomography, and rapid texture analysis. Two double-disk choppers will prevent frame overlap and a T0 chopper will remove fast neutrons and gamma radiation. A supermirror straight neutron guide will transport neutrons to an aperture selector at 46 m from the moderator, offering a choice of apertures including one open position for the beam to pass through for diffraction experiments. The distance from pinhole selector to the sample position is 10 m. The resolution Δλ/λ for energy-selective imaging will be better than 0.8%. A single-frame mode with a wavelength bandwidth of 6 Å, and a double-frame mode with a bandwidth of 12 Å, will benefit both imaging and diffraction experiments. For texture and strain analysis IMAT will have a high neutron flux at medium resolution, ideal for time-dependent in-situ loading and in-situ processing studies. 

The main instrument components for the two operating modes, imaging and diffraction, are summarised in Table 1. An initial assessment of the neutron performances of both modes has been carried out by Monte Carlo simulations using McStas [1, 2] (Table 2). The incident energy spectra and timing resolution requirements for both modes are similar, which is the prerequisite for a combined instrument on the same moderator. 

Instrument Parameters

Table 1: Main instrument components.

GeneralModeratorcoupled, L-H2/S-Ch4 (W5 port on TS-2)
Repetition rate5, 10 Hz
Neutron guidem=3, straight, square
100×100 mm2 in 2 m long shutter section
95×95 mm2 for ∼42 m guide
ChoppersT0 (20 Hz), 2 double-disk choppers (10 Hz)
Single frame bandwidth0.68-6.8 Å
Double-frame bandwidth2-14 Å
Flight path56 m to sample
ImagingL: distance pinhole-sample
D: Aperture diameter
L/D
10 m

5, 10, 20, 40, 80 mm

2000, 1000, 500, 250, 125
Max Field of View200×200 mm2
Detector typesGated CCD camera/ZnS-LiF scintillator
High-resolution Bragg edge pixel detector
   
DiffractionSecondary flight path2 m at 90 degree
Detector typeWavelength-shifting fibre coded ZnS
Detector coverage4 steradian (1 sr at 90 degree; Stage-1)
Minimum gauge volume1×1×1 mm3
   
Sample positioningHeavy duty Ω-XYZ system (1.5 t) + Tomography rotation stage
2 Theodolithes; Touchprobe or laser tracker
SScanSS software package [3,4]
Sample preparation
and storage
Sample preparation and analysis laboratory
Storage space for activated samples
Safe and humidity/ temperature controlled storage space
Storage space for collimator sets

 

Table 2: Expected performance parameters of IMAT evaluated by Monte Carlo calculations.

Imaging

Wavelength resolution

Δλ/λ=0.7% (at 3 Å)

Gated CCD:

 

Max. Field of View (FOV)

200×200 mm2

Best spatial resolution:

 

     FOV=200×200 mm2

200 μm + above

     FOV=100×100 mm2

100 μm

     FOV=80×80 mm2

80 μm

     FOV=50×50 mm2

55 μm

High-resolution Bragg edge pixel detector:

Based on Tremsin-MCP detector specification

Max. Field of View (FOV)

30×30 mm2

Best spatial resolution

50 μm

Timing resolution

<1 μs

Estimated (typ.) counting times:
     White-beam radiography                  1-60 s
     λ-dependent radiography(CCD)       1-10 min, per λ-slice
     Full TOF spectrum MCP                   10 min-2 hours
     White-beam tomography                   2-6 hours

 

 

 

Diffraction

Integral neutron flux on sample [n/cm2/sec]

2×107

Single frame d-spacing range:
         20 deg                                           2-20 Å
         45 deg                                           0.9-8.9 Å
         90 deg                                           0.5-4.8 Å
         125 deg                                         0.4-3.8 Å
         155 deg                                         0.35-3.5 Å

Horizontal divergence

< 0.2 degree

Spectral resolution Δd/d

0.7% (3 Å) at 90 degree

Strain resolution

70 microstrain

Estimated (typ.) counting times:
        For one diffraction pattern               5-60 min
        Texture (ODF)                                 5-60 min

References

[1] K. Lefmann, K. Nielsen, McStas, a General Software Package for Neutron Ray-tracing Simulations, Neutron News, 10 (3), 20-23, (1999)

[2] P. Willendrup, E. Farhi, K. Lefmann, McStas 1.7 – a new version of the flexible Monte Carlo neutron scattering package, Physica B, 350, 735-737 (2004)

[3] J.A. James, J.R. Santisteban, L. Edwards, M.R. Daymond, A virtual laboratory for neutron and synchrotron strain scanning, Physica B: Condensed Matter, 350 (1), 743-746 (2004)

[4] J.A. James, L. Edwards, Application of robot kinematics methods to the simulation and control of neutron beam line positioning systems, Nucl. Instr. Meth. A, 571 (3), 709-718 (2007)

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