ITN

Small Angle Neutron Scattering Spectrometer, EPA

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F.G. Carvalho, F.M.A. Margaça, A.N. Falcão, J.Neves, A.Saraiva, J.S. Sousa and J.F. Salgado

Small Angle Neutron Scattering, SANS, provides one of the best-suited tools for the characterisation of materials microstructure in the range 1-100 nm. It provides information on the shape, size and volume fraction of heterogeneities in the bulk, at the colloidal scale. Nowadays, there is interest in producing homogeneous structures or extremely fine-scale second phases in quite different materials. The characterisation of such materials at this spatial scale is thus particularly important so that the demand for SANS instruments is increasingly high, world-wide.

EPA, the SANS facility designed for installation at the Unit of Reactors and Nuclear Safety is a medium resolution SANS instrument, with relatively good detector count rate, for a range of Q-values of 0.01 Å^-1 – 0.5 Å^-1. These characteristics of EPA enable the application of SANS to different fields of research such as Physics, Biology, Metallurgy, Polymer Science and Geology. The expected instrument’s performance, in spite the modest RPI flux and the absence of a cold source, follows from the previous extensive work carried out at ITN on instrument design optimisation (Margaça et al., Nucl. Instrum. Methods, A274, (1989) 606; J. Appl. Cryst. 24 (1991) 994 and Falcão et al., J. Appl. Cryst. 27 (1994) 330). The EPA general layout is shown in Fig.1. The in-pile and shielding parts of EPA have also been optimised by means of MCNP simulation (Gonçalves et al., Rad. Prot. Dos. 116 (2005) 562).

Fig.1: General layout of EPA.1-neutron scatterer; 1a-ends of the water circuit; 2-in-pile collimator assembly; 3-beam shutter; 4-mechanical velocity selector; 5-out-of-pile collimator; 6-sample chamber; 7-position sensitive detector; 8-shielding walls. DIDE is the nearby 2-axis diffractometer facility and ETV a time-of-flight diffractometer.

The hardware of EPA has been installed and the command and control electronics and data handling protocols have been essentially completed and tested.

The alignment of the various components and equipments of EPA was resumed. Detailed test work of the facility has shown that an enhanced signal to noise ratio requires further improvement of the shielding and the installation of a 20 cm long Be filter. The design of a liquid N2 cryostat to cool this filter is under way.

Research activities planned in the organic-inorganic hybrid materials project will immediately benefit from the availability of the EPA instrument whose operation should begin as soon as possible.