MSUG Newsletter

Since the last user group meeting there have been many changes made to the instruments and staff of the crystal analyser group at ISIS. Recently it was announced that Colin Carlile, head of ISIS Science Spectroscopy and Support Division, has been offered the position of British Director of the ILL. We wish him well at this ‘continuous’ challenge and we shall no doubt see him at the annual NBUMS meetings.

TOSCA

Considerable progress has been made on TOSCA, which is the replacement for TFXA. The instrument design uses a larger number of detector banks. These are correspondingly more difficult to shield and some effort has been devoted to substantially improving this shielding, introducing some collimation and modifying the cryostat. The cryostat itself is a triple-headed closed-cycle device that has a base temperature of 12K. Occasionally temperatures down to 1.5K are required and a special liquid helium centre-stick has been constructed to address this need.

The diffraction detector bank in near-backscattering has been re-installed and calibrated and is now routinely available.

The major focus for the immediate future is the design of its second phase, TOSCA II. This is scheduled for installation during the shutdown in the first spring of the new millennium. The basic concept is clear: the forward scattering detector bank on TOSCA II will closely resemble the current backscattering bank i.e. a graphite analyser and a cooled beryllium filter. The details are being finalised and the project is on track for time and finance.

As always, the science on TOSCA is both varied and exciting. Catalysis continues to form a large part of the programme, studies of the adsorption of probe molecules on catalyst supports have been very successful, as have studies of precursors for the active species on ammoxidation catalysts. Work on model compounds for surface species, that are apparently well understood has shed new light on the dynamics and prompted revisions of the assignments. Hydrogen-bonded materials are still a source of intense interest for biological systems and crystal engineering applications. Ice in its many manifestations is a major focus of activity.

OSIRIS

The OSIRIS instrument is, for scientific purposes, scheduled as a diffractometer and operates in this mode for up to 50% of the time. Many important instrumental aspects have been tested with most sample environment; for example the 7T magnet can be used without causing detector problems. Recent users were able to use the first diffraction detector module. A further two modules will shortly be available, during the next cycle, which will lead to a tripling of the neutron data-rate. The remaining five modules will be installed as they become available

The other 50% of the instrumental time is used for tests on the new polarisers and analysers. The OSIRIS project development team of David Martin and Dennis Engberg has been joined by the new instrument scientist, Dr. Ken Andersen. Ken was formerly instrument scientist on the polarisation spectrometer, D7, at the ILL. This appointment will accelerate the progress of development work. It is planned that incident beam polarisation will be ready for users in about six months time and for "Full Polarisation Analysis" to be available in the year 2000!

eVS/VESUVIO

In 1998 a European Union Award of 800,000 ECU was forthcoming for the development of user access to neutron beams of the highest energy, the VESUVIO project. This collaboration between ISIS, University "Tor Vergata" in Rome and Liverpool University in the U.K. is progressing well. At present a new filter cooling and cycling device is being designed in Rome and this will be ready for installation early in 2000. This device will explore improvements to the resolution, by about two. Tests on possible new types of detector are in progress at ISIS and once a final decision on the type of detector to be used has been made, construction will start with the aim of installing a new large angle circular detector early in 2001. This will increase the count rate by about three.

An important new software development is the installation of new programs for reconstructing the three dimensional momentum distribution of atoms in single crystal samples, in collaboration with Professor George Reiter of the University of Houston. All instrumental effects are removed from the data by the program and the data is reduced to between 10 and 20 coefficients, which measure anharmonicity in the potential. It is, in effect, a new type of neutron spectroscopy. The coefficients can be compared directly with theoretical calculations or in systems with inversion symmetry, one can directly reconstruct the wave function and potential energy surface of the atom in a model independent way. The method is thought to be particularly useful for hydrogenous systems such as metal hydrides and hydrogen bonded systems.

A VESUVIO workshop is planned for November 26-27 1999 at Cosener’s House, Abingdon. The workshop will discuss the types of measurements, which can be made on eVS and will be illustrated by talks from users. The VESUVIO project and the impact it will make will also be discussed. Another important aim of the workshop is to investigate new fields of interest for eV neutrons. Members of the molecular sciences user group would be particularly welcome. Details of the workshop can be obtained from Andrew Fielding (A.L.Fielding@RL.AC.UK) or Jerry Mayers (J.Mayers@RL.AC.UK).

IRIS

A major change on IRIS has been in its physical environment. The installation of OSIRIS led to a radical re-think of the space available in what is now the IRIS/OSIRIS area. New work-benches and storage cupboards have been purchased and installed which have actually improved matters for the IRIS users.

The science carried out on IRIS continues to be world class with more publications produced in 1998/99 than on any other spectrometer at ISIS.

The move towards studies of magnetic systems and quantum fluids continues apace. Layered manganese perovskites and a very high accuracy study of the roton dispersion curve in superfluid liquid helium being particularly fruitful. Both these areas of research require the use of specialised low-temperature equipment such as dilution refrigerators and sorption cryostats and much effort has been put in to ensuring that these types of experiments are made more straightforward by installing new control software based upon the commercial LABVIEW © package.

The new liquid-helium-cooled graphite analyser project is nearing completion and final installation is expected to take place in September. This should give a factor ~ 2.5 increase in count-rate with an associated improvement of signal-background from 1350:1 to 5000:1.

All-in-all, the last six months have been as busy as ever and the next six months will no doubt be the same with plans already taking shape for development work to be associated with the proposed ISIS second target station project.

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