Enhanced Performance of Small Angle Neutron Scattering at the McMaster Nuclear Reactor

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The aim of this Research Tools and Instruments grant application is to enhance the performance of the “Small Angle Neutron Scattering for Nanoscale Materials” (MacSANS) instrument at the McMaster Nuclear Reactor (MNR). This neutron scattering instrument is currently completing construction. When operational in 2021, it will be one of only two neutron scattering instruments in Canada (the other is the MAD neutron diffractometer, also at the MNR). The enhanced performance of the MacSANS instrument, which this RTI grant application will enable, will occur via two modifications to the original design: (1)We will take full advantage of the large detector vessel of the instrument and allow for vertical translation of the 1 m2 position-sensitive neutron detector, by up to 0.5 m. This improvement will extend the instrument's length-scale sensitivity by about 130% by increasing the accessible range of momentum transfer, Q, or scattering angle, range of the instrument by ~ 50%; and (2) We will increase the neutron flux by replacing the polycrystalline lead aggregate filter in the primary flight path of the instrument with a single crystal lead filter. The lead is necessary to reduce the gamma radiation in the incident neutron beam. However, the current polycrystalline lead aggregate also attenuates the desired neutron beam intensity, unless the wavelength of the incident neutron beam is greater than the Bragg cut-off for lead, which is about 6 . The net effect of this is that a polycrystalline lead aggregate filter restricts the incident neutron beam to neutrons with wavelengths greater than ~ 6 , whereas an appropriately configured single crystal lead filter could be used with neutrons of any wavelength. Operation of the MacSANS instrument with incident wavelengths of ~ 4 , for example, would allow both extended Q, or scattering angle, coverage, and also increased incident neutron beam fluxes, of up to factors of ~ 4. Taken together, these two enhancements will increase both the Q range of the instrument and its neutron intensity. Hence these enhancements will increase the sensitivity of the instrument both in terms of the signal and the dynamic range of the length scale of the nanoscale of the material being probed. The enhancements of the MacSANS instrument that we seek to make via this RTI application will impact a large and pan Canadian community of Canadian scientists and engineers with interests in nanostructure in materials. The PI and 8 co-applicants presently supervise some 74 HQP, and are representative of a much larger community who will take advantage of this highly specialized research infrastructure. These enhancements are also leveraging ~ $7M in prior investments by CFI ($3M), ORCDF ($3M) and McMaster University ($1M) for the original design and construction of MacSANS.