The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o

Water dynamics in cement pastes

Cement has been used for centuries as a cost effective construction material,as well as for the conditioning of lowlevel radioactive waste. The interaction of water with calcium silicate hydrate the main component of cement paste,CS H is one of the prime factors for controlling the stability of the cement paste in the environment. However,much of the material science of cement hydration,including the bonding and interaction of water with C S H,remains unknown. Here we used high resolution quasi elastic neutron scattering to investigate the water dynamics on cement pastes hydrated for more than 28 days with different levels of hydration on the nanosecond time scal

Water dynamics in hardened ordinary Portland cement paste or concrete from quasielastic neutron scattering

Portland cement reacts with water to form an amorphous paste through a chemical reaction called hydration. In concrete the formation of pastes causes the mix to harden and gain strength to form a rock like mass. Within this process lies the key to a remarkable peculiarity of concrete it is plastic and soft when newly mixed, strong and durable when hardened. These qualities explain why one material, concrete, can build skyscrapers, bridges, sidewalks and superhighways, houses and dams. The character of the concrete is determined by the quality of the paste. Creep and shrinkage of concrete specimens occur during the loss and gain of water from cement paste. In order to better understand the role of water in mature concrete, a series of quasi elastic neutron scattering QENS experiments were carried out on cement pastes with water cement ratio varying between 0.32 and 0.6. The samples were cured for about 28 days in sealed containers so that the initial water content would not change. These experiments were carried out with an actual sample of Portland cement rather than with the components of cement studied by other workers. The QENS spectra differentiated between three different water interactions water that was chemically bound into the cement paste, the physically bound or glassy water that interact with the surface of the gel pores in the paste and unbound water molecules that are confined within the larger capillary pores of cement paste. The dynamics of the glassy and unboud water in an extended time scale, from a hundred pico seconds to a few nano seconds, could be clearly differentiated from the data. While the observed motions on the pico second time scale are mainly stochastic reorientations of the water molecules, the dynamics observed on the nano second range can be attributed to long range diffusion. Diffusive motion was characterized by diffusion constants in the range of 0.6 2 10 9m2 s, with significant reduction compared to the rate of diffusion for bulk water. This reduction of the water diffusion is discussed in terms of the interaction of the water with the calcium silicate gel and the ions present in the pore wate

Dynamical disorder and reorientation of the CH3 groups in N methylacetamide

By selective deuteration the influence of the environment on the geometry of the motion of each hydrogen group in N methylacetamide NMA, CH3NHCOCH3 was probed using quasi elastic neutron scattering. From 100 K to ambient very good agreement was obtained over the entire Q range 0.35 to 2.35 A , by fitting the data to a uni axial rotational model of the methyl groups around the C3 axi

Different dynamics of chiral and racemic L and DL serine crystals Evidenced by incoherent inelastic neutron and Raman scattering

Interest in chiral vs racemic amino acid forms stems from their different solid state properties associated to the packing arrangement that leads to starkly different physical behavior. Here we focus on the different dynamic properties of the chiral L form and racemic DL form crystals of serine, C3H7NO3 . Measuring incoherent inelastic neutron and Raman scattering over a wide temperature range we could asses a subtle dynamical transition in L serine near 150 K. The difference in the dynamic properties of the crystals of L and DL serine evidenced from our spectroscopic studies is in a good agreement with the different Cp T dependences and different structural strain of the two forms on cooling. Despite a higher bulk density, the molecular fragments in the crystals of L serine are more dynamic than in DL serine, and this manifests itself in the incoherent inelastic neutron and Raman spectra, as well as in a higher heat capacity, a higher thermal expansion coefficient, or in the NMR spectr