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ISIS neutron source
From Wikipedia, the free encyclopedia
The ISIS neutron source is currently (2006) the most powerful spallation neutron source in the world. Situated at the Rutherford Appleton Laboratory in Oxfordshire, United Kingdom, it is used to enable 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.
It currently (2007) generates the most powerful neutron beam of any such facility in the world, but may possibly be overtaken in this by the Spallation Neutron Source currently being constructed at Oak Ridge, Tennessee.[1]
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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 160 kW 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.
ISIS is administered and operated by the CCLRC, and funded by it in partnership with European Union's Neutron and Muon Integrated Infrastructure Initiative. 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, the control room is staffed 24 hours a day, every day of the year. 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.
The source was approved in 1977 for the RAL site on the Harwell campus and recycled components from earlier UK science programmes including the accelerator hall which had previously been occupied by the Nimrod accelerator. The first beam was produced in 1984, and the facility was formally opened by the then Prime Minister Margaret Thatcher in October 1985.[2]
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. The name was selected for the official opening of the facility in 1985, prior to this it was known as the SNS, or Spallation Neutron Source. The name was considered appropriate as Isis was a goddess who could restore life to the dead, and ISIS made use of equipment previously constructed for the Nimrod and Nina accelerators[3].