The ISIS Neutron and Muon Source is a pulsed neutron and muon source at the Rutherford Appleton Laboratory (RAL) of the Science and Technology Facilities Council (STFC), on the Harwell Science and Innovation Campus in Oxfordshire, United Kingdom. It has been operating since 1984. It uses beams of neutrons and muons to allow the study of materials at the atomic and molecular level. It has a suite of 35 instruments, each of which is individually optimised to investigate different aspects of atomic- and molecular-level properties. The research conducted at ISIS plays an important role in addressing global challenges, answering fundamental questions, and delivering scientific and socio-economic impact. Hundreds of experiments are performed every year at the facility by industrial and academic researchers from around the world, in diverse science areas such as clean energy, advanced manufacturing, quantum computing, healthcare, agriculture and archaeology.
Background physics Neutrons are uncharged constituents of atoms and penetrate matter well, deflecting primarily from atomic nuclei. The statistical accumulation of deflected neutrons at different positions beyond the sample can be used to find the atomic structure of a material, and the loss or gain of energy by neutrons can reveal atomic-level dynamics, for example ionic diffusive processes in solids. They are good at studying where atoms are and what atoms are doing. At ISIS, the neutrons are created by accelerating "bunches" of protons in a synchrotron, then colliding these with a tungsten target. The impacts cause neutrons to spall off the tungsten atoms, and the neutrons are channelled through guides, or beamlines, to around 30 neutron instruments. The target stations and most of the instruments are set inside two large halls known as target stations. Since the proton beam is pulsed, the energy of the neutrons that are produced can be determined by time-of-flight (TOF) techniques – this is a key bit of information needed to study atomic-level structures and dynamics. ISIS is one of several proton accelerator-based neutron sources in the world, alongside J-PARC in Japan, SNS in the US, the CSNS in China and the European Spallation Source currently under construction in Sweden. ISIS Neutron and Muon Source 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 the muon instruments – ISIS has 7 different muon experiment areas, five of which are normally in use. ISIS was approved in 1977 for the RAL site on the Harwell campus and used recycled components from earlier UK science programs, including the accelerator hall, which had previously been occupied by the Nimrod accelerator. The first neutron beam was produced in 1984, and the facility was formally opened by the then Prime Minister Margaret Thatcher in October 1985. 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 chosen for the official opening of the facility in 1985; before this it was known as the SNS, or Spallation Neutron Source. The name was considered appropriate as Isis was a deity who could restore life to the dead, and ISIS made use of equipment previously constructed for the Nimrod and NINA accelerators. The second target station (TS2) was given funding in 2003 by Lord Sainsbury, then science minister, and was completed on time and budget, with first neutrons delivered to seven instruments on 2 August 2008. In March 2011, the Science Minister, David Willetts, gave a £21 million investment to build four further instruments. TS2 uses lower-energy neutrons to study soft condensed matter, biological systems, advanced composites and nanomaterials. In 2023, £90 million of funding was announced for the Endeavour programme that, over the subsequent decade, will bring two new instruments to the facility, as well as six significant upgrades to existing instruments. The build of these instruments began in 2025, with the first planned to begin operations in 2028. ISIS Neutron and Muon Source was originally expected to have an operational life of 20 years (1985–2005), but its continued success has led to a process of refurbishment and further investment, intended to advance the facility and extend the life of ISIS beyond 2040.
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