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Neutron spin-echo spectroscropy

The ILL has firmly established itself as a pioneer in neutron science and technology. Neutron beams are used to carry out frontier research in diverse fields.

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Neutron techniques

Neutron spin-echo spectroscopy

A remarkable technique called neutron spin-echo, pioneered at the ILL by a Hungarian physicist, Ferenc Mezei, offers a highly sensitive method for following very slow dynamic processes in soft matter. It takes advantage of an important property of neutrons – their spin. The neutrons are first polarised so that their spins are all in the same direction and then passed through a magnetic field. This causes the spins to wobble, or precess (like a spinning top). The number of precessions depends on the time each neutron takes to traverse the field, which in turn depends on its energy. After being scattered by the sample, the neutrons pass through a second magnetic field, which winds back the spins through the same number of precessions (a sort of ‘echo’) over the same period of time so that the spins achieve their original orientations. If, however, some of the neutrons have lost or gained energy by interacting with the sample molecules, they will not all end up with the same spin polarisation. This deficiency then provides a neat way of measuring tiny energy changes associated with slow movements such as that of a polymer chain sliding through the tangled chains in a melt.

The ILL has several instruments for measuring inelastic scattering including IN5, IN6, IN11, IN15 and IN16 used in soft-matter studies.