Feasibility study of the transfer of the neutron resonance spin-echo spectrometer MUSES from continuous reactor to pulsed source

The Orphée reactor, located at the CEA Saclay near Paris, that was used to produce neutrons for scattering experiments over the past four decades has been stopped definitively in October 2019. The Laboratoire Léon Brillouin, the laboratory that operated the diffractometers and spectrometers around the Orphée reactor, is studying the possibility to build a compact Neutron Source to keep offering neutron beams to the French neutron scattering community. The efficient use of a pulsed source requires neutron instrumentation using Time-of-Flight (TOF) principles.The transfer of NSE spectrometer from continuous to pulse source requires the change of monochromatic neutron beam spin-echo technique to the TOF one. Here we report a successful attempt of adaptation of the Neutron Resonance Spin-Echo spectrometer MUSES (G1bis) to a pulsed source with a frequency of 20 Hz and a duty cycle of roughly 5 %.

Dramatic influence of patchy attractions on short-time protein diffusion under crowded conditions

In the dense and crowded environment of the cell cytoplasm, an individual protein feels the presence of and interacts with all surrounding proteins. While we expect this to strongly influence the short-time diffusion coefficient Ds of proteins on length scales comparable to the nearest-neighbor distance, this quantity is difficult to assess experimentally. We demonstrate that quantitative information about Ds can be obtained from quasi-elastic neutron scattering experiments using the neutron spin echo technique. We choose two well-characterized and highly stable eye lens proteins, bovine α-crystallin and γB-crystallin, and measure their diffusion at concentrations comparable to those present in the eye lens. While diffusion slows down with increasing concentration for both proteins, we find marked variations that are directly linked to subtle differences in their interaction potentials. A comparison with computer simulations shows that anisotropic and patchy interactions play an essential role in determining the local short-time dynamics. Hence, our study clearly demonstrates the enormous effect that weak attractions can have on the short-time diffusion of proteins at concentrations comparable to those in the cellular cytosol.