Liquid Bridges

 

2b. LOQ pit photographs

This picture shows the beam and samples on the rack.

This picture gives the same view as previous, except with the detector hood cover removed for clarity.

LOQ specifications

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	0.008 - 0.24 Å^-1  (main detector), 
			0.15 - 1.4 Å^-1 (new high-angle bank)

Dynamic range in Q	30 (on main detector), 175 (simultaneous use of all detectors)

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.

Instrument

ISIS Beam line 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 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 2x10⁵ cm^-2 s^-1 (ISIS at 50Hz, 200 mA 800MeV proton beam, tantalum target). Secondary flight path Evacuated tank to main detector.

Detector³He-CF₄ filled ORDELA "area" detector 15.15 m from moderator. Active area is 64 cm x 64 cm. Detector mapping under software control. External, annular, high-angle, scintillator "area" detector bank 11.6 m from moderator (from mid-1996).

Computer System

Data Acquisition		Standard ISIS DAE (DAE I).

Hardware			DEC VAXstation 3200 with colour monitor.  1.6Gb fixed disk
			(allows online storage of data for about 1 ISIS cycle).  EtherNet
			connection to ISIS HUB computer (twin VAX 4000 Model 500's
			with WORM optical storage unit).  Also i486 PC running MS
			Windows NT and an additional Tektronix-type terminal.  A 
			25-pin RS232 connection to an ISIS terminal server is also
			 available for users with laptop computers.

Software			VAX VMS 7.1 operating system, GENIE, COLETTE
			(instrument-specific data reduction in one or two dimensions
			 either online or fromfile), FISH (sophisticated model-fitting),
			VULOQ (data visualisation, colour and b/w, 1D, 2D and 3D
			 plotting).  SANDRA (data manipulation utility)

Sample Environment

Control			Standard ISIS CAMAC where used.  PC control is also available.
			User-supplied monitoring equipment can be interfaced provided
			that sufficient notice is given.

Standard			In air.  Alignment laser to position samples.  Computer-controlled
			 sample changer connected to computer-controlled water/oil bath
			 (-20 to +95 degrees C) taking any two of; two 10-position racks
			 for 10 mm wide quartz cells (maximum path-length 10 mm) or
			 two 4-position racks for 50 mm x 50 mm cadmium masks with
			 various diameter apertures or two 8-position racks for 20 mm
			 wide quartz cells or two 9-position racks for disc-shaped quartz
			 cells.  A 4-position rotating sample rack, a nitrogen gas purge,
			 electrical heaters and Pt-100 or K-type thermocouples are also 
			available.

Non-standard		"Orange" helium cryostat, closed-cycle refrigerator, RAL furnace, (Must be requested on	Newport electromagnet (for field across neutron beam),
proposal)			Goudsmit electromagnet (for field across or along neutron beam),			
			Couette-type and Poiseuille-type shear flow cells (please contact
			the instrument scientists). Other apparatus, including a 1 kbar
			Pressure Cell, may be available through negotiation with the
			relevant University groups (please discuss your requirements).
			User-supplied apparatus.

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Instrument Setups

 

LOQ is normally operated in one of the following three basic configurations. In decreasing order of usefulness, they are:

Please note that the chopper phases in the above table are illustrative examples only. Actual phases may differ from the above values, particularly after chopper maintenance, by as much as 100 us. All of the data in the above table assumes a chopper sector opening of 126 degrees. Other configurations of LOQ may be possible, please consult the instrument scientists.

Defining Distances

Lm-s is the moderator-to-sample distance, and Ls-d is the sample-to-detector distance. Both values are given in metres.

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Comparison of 4 Leading SANS Instruments

(With acknowledgements to "The Yellow Book", Guide To Neutron Research Facilities At The ILL, April 1994 and the 1994 World Directory of SANS Instruments compiled by K Ibel)

This table has been compiled for the benefit of potential users with the best intentions from the best available information.