Spin-echo technique with time-gradient magnetic fields for small-angle neutron scattering and reflectometry

A new neutron spin-echo technique based on the use of time-gradient magnetic fields, TGF NSE, can be used for purposes of small-angle neutron scattering and reflectometry. It employs linearly rising magnetic fields that can be created in simple solenoids or thin magnetic foils, thus allowing for a construction of long spin turners that can be tilted to rather small incident angles as required for high-resolution angular measurements. However, in contrast with the use of static or radio-frequency magnetic fields as in the well-known SESANS, the use of time-gradient magnetic fields results in the unusual dependence of the spin-echo length on neutron wavelength-λ3 rather than λ2. This allows for a significantly higher Q-resolution and for a very significant increase of Q-range with the latter feature especially valuable for the time-of-flight operation mode with pulsed neutron sources. We will consider the TGF spin-echo small-angle neutron scattering/reflectometer setup in detail and compare its parameters with those of the state-of-the-art SESANS instrument OFFSPEC at ISIS.