Neutron spin echo spectroscopy

The ideal complement to SANS to observe the temporal developement of structures under observation under equilibrium conditions is neutron spin echo spectroscopy. With the J-NSE instrument at FRMII, the NSE instrument at SNS in Oak Ridge, instruments at IN15 and also shortly WASP at ILL, a wide spectrum of measurement options are available to JCNS.

The result of a SANS measurement is analogue to a snapshot of the structure, data from an NSE measurement can be seen as being approximately analogue to images with multiple long exposure times. The time parameter is the adjustable Fourier time (typically between 0.005ns .. 500ns). The NSE signal delivers the correlations of the scattering structures which are still available after this time lag. The times involved are significantly shorter than those obtainable using a kinetic SANS measurement.

With a kinetic measurement, the reaction of a synchronous macroscopic “disturbance” is measured. However, NSE measures the correlation time of thermal fluctuations (Brownian motion). In this way, diffusion and relaxation processes can be observed on a molecular level in polymer melts, solutions, proteins and other soft matter systems on their typical length and time scale.