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Two World Records Fine print is much easier to read under a spotlight than a penlight in an otherwise dark room. The human eye needs a bright light—a high concentration of photons—to resolve the letters. For scientists using neutron scattering to determine the arrangements and motions of atoms and molecules in a material, the concentration of neutrons in a beam is critical. The higher the concentration, the "brighter" the beam is. With a very bright beam, scientists can obtain experimental data not possible when working with less intense neutron beams. For that reason, in November 2007 ORNL researchers were excited to learn that the recently upgraded High Flux Isotope Reactor may have set a world record for cold neutron beam "brightness." The concentration of slow neutrons available for experiments at HFIR may have exceeded the cold neutron record established by the Institut Laue Langevin research reactor in Grenoble, France. Lee Robertson, who leads the instrument development group and conducted the time-of-flight experiments designed to determine the brightness of the new cold source, said he and his colleagues measured a peak brightness exceeding ten trillion neutrons per unit solid angle per square centimeter per angstrom per second (the units in which source brightness is measured). Uncertainty about whether HFIR equaled or surpassed ILL's record stems from the lack of sufficiently detailed data on the brightness of other cold sources. Recent experiments already performed on the two new world-class, small-angle neutron scattering instruments at HFIR range from experiments examining the nature of radiation damage in materials to studies of the structure of complex polymeric materials formed from branched chains (including "comb" structures that have long linear chemical chains with short attached side chains). Before the recent upgrade, HFIR lacked the cold neutrons that have been available for years at other neutron scattering facilities. Cold neutrons are slower and have a longer wavelength than HFIR's thermal neutrons. Now that HFIR has a "cold source," which contains liquid hydrogen for slowing down the medium-fast thermal neutrons after they are reflected by the beryllium reflector surrounding the reactor core, experimenters can obtain more detailed information on biological and organic materials, such as proteins and polymers. Meanwhile, the Spallation Neutron Source surpassed the world record for beam power for an accelerator-based source of neutrons. The SNS operated at 183 kilowatts last August; the previous record of 160 kw for beam power was held by the United Kingdom's ISIS facility. Although a world record, the beam power has reached only about 10% of ultimate capability at the SNS.
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