ISIS Neutron and Muon Source
The ISIS facility is a scientific research institution, situated at the Rutherford Appleton Laboratory in Oxfordshire, UK. It contains a pulsed or spallation neutron source, the most powerful in the world, which enables muon and neutron scattering science to probe the structure and properties of matter, from the atomic to the biological scales. It provides a powerful research tool for universities and companies across many disciplines, including physics, chemistry, materials engineering, biology and even archaeology.
Neutrons and muons
Neutrons are uncharged constituents of atoms and penetrate materials well, deflecting only from the nuclei of atoms. The statistical accumulation of deflected neutrons at different positions beyond the sample can be used to find the structure of a material, and the loss or gain of energy by neutrons can reveal the dynamic behaviour of parts of a sample, for example diffusive processes in solids. At ISIS the neutrons are created by accelerating 'bunches' of protons in a synchrotron, then colliding these with a heavy tantalum metal target, under a constant cooling load to dissipate the heat from the 160kW proton beam. The tantulum atoms slough off neutrons, and these are channelled through guides, or beamlines, to about 20 instruments, individually optimised for the study of different types of matter. The target station and most of the instruments are set in a large hall. The penetrating neutrons are a dangerous form of radiation so the target and beamlines are heavily shielded with concrete.
ISIS produces muons by colliding a fraction of the proton beam with a graphite target, producing pions which decay rapidly into muons, delivered in a spin-polarised beam to sample stations.
Science at ISIS
ISIS is administered and funded by the CCLRC in partnership with other countries. Experimental time is open to academic users from funding countries and is applied for through a twice-yearly 'call for proposals'. Research allocation, or 'beam-time', is allotted to applicants via a peer-review process. Users and their parent institutions do not pay for the running costs of the facility, which are as much as £11,000 per instrument per day. Their transport and living costs are also refunded whilst carrying out the experiment. Most users stay in a hostel on the site or at a CCLRC-run conference centre in Abingdon. Over 600 experiments by 1600 users are completed every year.
A large number of support staff operate the facility, aid users, and carry out research. Instrument scientists oversee the running of each instrument and liaise with users, and other divisions provide sample environment, data analysis and computing expertise, maintain the accelerator, and run education programmes.
ISIS was opened by then Prime Minister Margaret Thatcher in October 1985. The source had been approved in 1977 for the RAL site on the Harwell campus and recycled components from earlier UK science programmes including the accelerator hall. Among the important and pioneering work carried out was the discovery of the structure of high-temperature superconductors and the solid phase of buckminster-fullerene.
A second target station is funded and under construction, due to open in 2007. It will use low-energy neutrons to study soft condensed matter, biological systems, advanced composites and nanomaterials. To supply extra neutrons for this, the accelerator is being upgraded.
The name ISIS is not an acronym: it refers to the Ancient Egyptian goddess and the local name for the River Thames.