LOQ normally operates at 25 Hz but 50 Hz operation over one half of its normal wavelength range is possible and sometimes advantageous (see the section on Instrument Setups). Please contact the instrument scientists if you think 50 Hz operation may be of use to you.
|Incident wavelengths||2.2 - 10.0 Å at 25 Hz, 2.2 - 6.7 Å or 6.3 - 10.0 Å at 50 Hz|
|Momentum transfer, Q||0.006 - 0.24 Å-1 (main detector)|
0.15 - 1.4 Å-1 (high-angle bank)
|Dynamic range in Q||40 (on main detector), 230 (simultaneous use of all detectors)|
If the ratio of H:D present in a hydrogenous sample is more than 50% H the sample path-length (thickness) should ideally 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||N5, viewing the 25 K liquid hydrogen (lower) moderator.|
|Primary flight path||Soller supermirror bender (24 mrad, to remove neutrons with wavelengths less than 2 Å), upstream scintillator monitor, aperture dial No 1, variable-opening (2 - 126 degrees) disc chopper, frame overlap mirror (removes neutrons with wavelengths greater than 12 Å), 3 m evacuated flight tube, sample position scintillator beam monitor, aperture dial No 2, final collimation tube.|
|Sample position||Around 11.1 m from moderator. Approximate size is 0.4 m (parallel to beam) by 1.5 m. No height restriction. Beam is approximately 0.63 m above base plate. Crane access possible (SWL 1000 Kg). Sample transmission scintillator monitor on motorised rack. Provided with water, helium and electrical services. Secondary, top-loading, in-vacuum sample position with limited access and services around 12.5 m from moderator (giving an approximate Q range of 0.01 - 0.34 Å-1).|
|Beam size at sample||Defined by aperture No 2 and final collimation. Between 2 - 20 mm diameter. Typically 8 mm diameter.|
|Neutron flux at sample||Dependent on collimation, ISIS accelerator performance and target type. Typical time-averaged flux is 2x10^5 cm-2 s-1 (ISIS TS1 at 40Hz, 160 uA 800 MeV proton beam, tantalum target).|
|Secondary flight path||Evacuated tank to main detector.|
|Detector||3He-CF4 filled ORDELA "area" detector 15.15 m from moderator. Active area is 64 cm x 64 cm with 5 mm resolution. Detector mapping under software control. External, annular, high-angle, scintillator "area" detector bank 11.6 m from moderator.|
RK Heenan, J Penfold & SM King, SANS at Pulsed Neutron Sources: Present & Future Prospects, J Appl Cryst (1997), 30, 1140-1147
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