Polarized neutrons for pulsed neutron sources

Polarized neutrons provide a powerful tool for research at today’s continuous neutron sources, permitting unique information to be obtained from neutron-scattering experiments and in the area of fundamental neutron physics. The information obtained is indispensable to important areas of current research such as magnetism, spin fluctuations in correlated-electron materials, nanoscience, astrophysics, and cosmology. Unfortunately, the polarized neutron capabilities that already exist at reactor neutron sources, mainly in Europe, cannot be transferred directly to pulsed spallation sources because many of the devices used at reactors to manipulate neutron spins operate only at a single neutron wavelength or with a neutron beam of limited divergence. Both of these restrictions must be overcome for devices to be useful at pulsed spallation sources. This report identifies the significant R&D efforts that will be required to achieve these goals. These efforts must be undertaken now, if they are to be useful early in the lifetime of the spallation neutron source (SNS) or its Japanese counterpart, Japanese proton accelerator research complex (J-PARC). A workshop on the use of polarized neutrons at pulsed neutron sources was held on February 10-13, 2003, in Gaithersburg, Maryland, USA. Sixty-one scientists representing work in Europe, Japan and the US attended the workshop whose purpose was to discuss research opportunities with polarized neutrons at pulsed spallation sources and to develop a roadmap for the technology R&D required to facilitate this type of work. Well-funded efforts to develop polarization capabilities are under way in both Japan and Europe. The workshop concluded that it makes sense for the US to collaborate with these activities, as well as to develop its own R&D program, as it is beginning to do. There is ample opportunity within the R&D portfolio outlined in this report for research activities both at universities and at national neutron centers. Synergy between these efforts will contribute to other goals such as the development of a robust programme of instrument innovation that will be required at new pulsed sources to maintain their vitality in future decades.