40 Years of Neutron Scattering: A Perspective

摘要

James Chadwick discovered the neutron in 1932, identifyingthe product of alpha-particle irradiation of beryllium as aneutral particle having about the same mass as the proton.Enrico Fermi led the team that demonstrated the first self-sustaining fission reaction in 1942, after which reactorsdeveloped rapidly, optimized for the use of thermal neutronbeams for studying materials properties. Eventually,research reactor designs met engineering heat transfer limitsthat constrain their performance (excellent, though it is).Now, new reactors are optimized more for special purposesthan for highest flux. In recognition of reactor flux limita-tions, accelerator-driven pulsed spallation neutron sourcesarose, capitalizing on averaging out the heat removalbetween intense source pulses and on the relatively lowerheat dissipation per useful neutron produced in spallation.Pulsed sources and the required time-of-flight methodsimproved over the years, and now, in terms of the peakavailable neutron flux, exceed the most powerful reactors.Recently, charged-particle reactions driven by low-energyaccelerators have come onto the scene, which are inexpen-sive to build and operate, and provide needed testing andtraining venues that support the large sources.