Purpose
SANS Xpress Access at ISIS is suitable for:
- new and infrequent users who want to test the feasibility of a potential SANS experiment prior to submitting a full proposal
- existing users that need to probe their results or systems further because they are not yet sufficiently well-understood, or well-developed, to warrant a proposal in their own right
- existing users that have a ‘desperate need’ to make a small number of additional measurements on samples related to their recent beam time proposals (eg, to complete a parametric data set, or ‘round-off’ a PhD thesis)
- the facilitation of ‘blue sky’ and/or ‘in-house’ research
- commercial users only requiring small durations of beam time and who are willing to accept ISIS involvement in the running of their samples – billing for this service is on a per hour basis.
But, please note, SANS Xpress Access is not intended to provide data of high statistical precision.
Principles
At least 1 day per cycle on each instrument will be devoted to Xpress Access. But it may also be possible to run small numbers of Xpress Access samples as and when the instrument schedules permit.
Due to its high over-subscription, Xpress Access samples will only be run on the SANS2D instrument when there is a clear and justifiable case for doing so.
No guarantee is given that measurements will take place on any particular day, even if advertised, and normal peer-reviewed experiments will usually take priority. When Xpress Access samples cannot be run as advertised they will be held over – subject to their useful lifetime – until a new measurement session can be scheduled, or will be returned to the user if so requested.
Above all, it is expected that Xpress Access samples will be straightforward and uncomplicated, and easily run on a sample changer.
Experimental considerations
We prefer to use an incident neutron beam collimated to between 8 - 12 mm in diameter so as to maximise the number of Xpress Access samples that can be mounted on the sample changer in one session.
The duration that each Xpress Access sample is measured for will be at the discretion of the instrument scientists on the day.
Measurements will normally be performed at 25°C (298 K). However, applicants may discuss other measurement temperatures in the range 5-95°C (ie, those possible with our normal circulator baths) with us. Temperature variation work will only be performed after all ambient temperature measurements are completed (to remove the possibility of thermally-induced damage to other samples), and only if time permits.
Do remember that you must consider, for example, a background solvent as an Xpress Access sample in its own right; i.e. if your sample is a surfactant or protein in an electrolyte solution you must not only supply that sample, but also the pure electrolyte solution!!!
If absolutely necessary the instrument scientists may agree to pipette supplied solutions into our own cuvettes. But the undertaking of any practical work beyond this is outside of the scope of Xpress Access. You should apply for Rapid Access instead.
Biological samples
Unfortunately it has been our experience that many biological samples sent for Xpress Access have been of poor quality, resulting in wasted beamtime.
Therefore, with effect from Autumn 2018, if you request Xpress Access for biological samples you should be prepared to be challenged for evidence of the samples purity and non-aggregation.
Sample containers
Solution/dispersion samples should be contained in quartz cuvettes of 1 mm or 2 mm path-length (Hellma stock codes 110, 120 or 404; Starna stock codes 21 or 32). Some powders can also be contained in 'open-top' or two-part ('dish-and-cover') cuvettes.
Solid samples and granular materials should be contained in aluminium foil 'envelopes'. Leave small 'wings' of foil (5 mm is plenty) on either side of the 'envelope' for mounting purposes. Ensure the filled area is between 10 - 15 mm across.
Sample shipping
Xpress Access samples may be sent by whatever route is appropriate to the hazard that they present, but is the legal responsibility of the sender to ensure that they comply with all necessary packaging, documentation and transport regulations.
Where ISIS supplies transport packaging it should normally be used for sample shipment.
Measurements
At the start of each Xpress Access session the Instrument Team will, as a matter of routine, measure:
- the scattering from an intensity calibration standard;
- the background scattering for the intensity calibration standard;
- the transmission of each of the above;
- a 'direct beam' transmission
They will then measure the scattering and the transmission of each supplied Xpress Access sample.
Data output
New and commercial applicants will be provided with fully reduced and corrected (ie, instrument-independent) data. More experienced applicants may simply be provided with details of the relevant files and expected to perform their own data reduction.
No analysis or interpretation of the data will be provided for any users, except where this is part of a separate collaboration or contract.
Beamtime limits
SANS Xpress Access must not be viewed as a way to circumvent the normal peer-review process associated with the Direct Access or Rapid Access mechanisms. For this reason, the Instrument Team reserve the right to cap excessive usage(*) and report those applicants to the relevant Facility Access Panel (FAP3). FAP3 may, in turn, require a Direct Access or Rapid Access proposal before further beam time is allocated.
(*) As a rough guide, more than 4 Xpress Access samples a cycle, or 12 Xpress Access samples a year.
Data policy
Data collected using SANS Xpress Access are subject to the normal ISIS policy regarding publication of scientific results, and bibliometric criteria, among others, will be used to assess the productivity of the scheme.
