Sans2d technical information

SANS2d is a second-generation time-of-flight small-angle scattering instrument combining the advantages of white beam techniques with TWO large independently-moveable area detectors.

Technical Summary

Incident wavelengths2.0 - 14.0 Å at 10 Hz
Momentum transfer, QDepends on sample-detector distances and detector offsets: Qmin~0.002 Å-1, Qmax~3 Å-1

Notes for proposers:

  1. Users are expected to provide their own sample cuvettes/cans. But where necessary, some quartz cuvettes are available for loan. Please discuss with the instrument scientists. ISIS does not endorse any particular manufacturer of quartz cuvettes but both Hellma (stock codes: 110, 120 & 404; material codes: QS/QX) and Optiglass (stock codes: 21 & 32; material code: Q) manufacture suitable products.

If the ratio of H:D present in a hydrogenous sample is more than 50% H the sample path-length (thickness) should not exceed 1 mm (or absorbtion, incoherent and inelastic scattering effects may manifest themselves).  Otherwise path-lengths of 2 mm are acceptable.  In predominantly deuterated and/or very dilute samples 5 mm path-lengths can be used.  Exceptionally 10 mm path-lengths may be necessary.

The volumes required for different 1 mm path-length cells are approximately (minimum in brackets):

10 mm wide rectangular -    0.25 ml  (0.15 ml)

20 mm wide rectangular -    0.55 ml  (0.40 ml)

disc-shaped ('banjo')     -     0.25 ml  (0.25 ml)

 

The advantage of disc-shaped cells and the 20 mm wide rectangular cells is that a larger diameter neutron beam can be used, increasing the count rate on the sample, where appropriate.

Instrument Parameters

Isis BeamlineE2, viewing the coupled cold moderator
Primary flight pathcNi super-mirror bender (to remove neutrons with wavelengths less than 1.5 Å), upstream scintillator monitor, overcount protection fast shutter, variable-opening counter-rotating disc chopper, 5 x 2 m moveable evacuated collimation sections (each with choice of Ni guide sections or plain pipe) for variable incident collimation, 5 moveable aperture strips (each with different size apertures), sample position scintillator beam monitor, sample aperture strip, final collimation tube.
Sample positionAround 19 m from moderator. Side access. No height restriction. Beam is approximately 1 m above base plate. Crane access possible (SWL <5000 Kg). Sample transmission scintillator monitor on motorised rack. Provided with water, helium and electrical services.
Beam size at sampleDefined by sample aperture strip and final collimation. Up to 15 mm diameter is possible, typically 8 mm diameter.
Neutron flux at sampleDependent on collimation, accelerator performance and target type. Typical time-averaged flux is currently estimated to be >106 cm-2 s-1 (ISIS TS2 at 10Hz, 40 uA 800 MeV proton beam, tantalum target).
Secondary flight pathEvacuated tank containing detectors.
DetectorsTwo 3He-CF4 filled ORDELA "area" detectors. Active area of each is 96.5 cm x 96.5 cm with 5 mm resolution. The detectors can be moved in the vacuum tank both along the beam (to vary sample-detector distance between 2 and 12 m) and to give a sideways offset (to extend the Q range at a given detector distance) of up to 1200 mm. The front detector can also be rotated to face the sample. Detector mapping under software control.

References

RK Heenan, SM King, DS Turner & JR Treadgold, SANS2D at the ISIS Second Target Station, Proc ICANS-XVII (2006), 780-785

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