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.
|Incident wavelengths||2.0 - 14.0 Å at 10 Hz|
|Momentum transfer, Q||Depends on sample-detector distances and detector offsets: Qmin~0.002 Å-1, Qmax~3 Å-1|
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.
|Isis Beamline||E2, viewing the coupled cold moderator|
|Primary flight path||3ΘcNi 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 position||Around 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 sample||Defined by sample aperture strip and final collimation. Up to 15 mm diameter is possible, typically 8 mm diameter.|
|Neutron flux at sample||Dependent 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 path||Evacuated tank containing detectors.|
|Detectors||Two 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.|
RK Heenan, SM King, DS Turner & JR Treadgold, SANS2D at the ISIS Second Target Station, Proc ICANS-XVII (2006), 780-785
|Other STFC||News||Site Sections||Important Links|