Zero Field Spin-Echo Technique

The most expensive parts of a conventional NSE instrument are the main solenoids providing the precession field. A closer look at Bloch s equation of motion for the spins (Eq. 2.11) shows that in a coordinate system that rotates with the precession frequency around Bg the spin is stationary, the coordinate system rotation is equivalent to the addition of - to all magnetic fields. By this means the large precession field inside the main coils may be transformed to zero - zero field spin-echo). The flippers are viewed as elements rotating 

This angle is preserved in the zero field region around the sample. In a symmetric flight path between two RF-flippers (RF radio frequency) in the scat- 

The complete instrument consists of two flippers with distance L before the sample and a symmetric set of two flippers after the sample. All flight paths between the first and the fourth (last) flipper are surrounded by magnetic shielding to yield the zero field condition that preserves the spin orientation. All RF flippers are operated synchronously, i.e. with the same current. Their field direction (i.e. rotation) is +, +. A neutron that enters the first flipper at a time 

An interesting variant of the resonance NSE is the so-called MIEZE technique [ 19]. Using two RF-flippers that operate at different frequencies a neutron beam is prepared such that a special correlation between a time varying spin rotation co= Qi-Q2) the velocity of the neutrons is achieved. An analyser after the second RF-flipper translates the spin rotation into an intensity modulation. The 

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The spin echo technique measures the ratio of the amplitude of the spin echo with and without the applied electric field, R Et), which is the Fourier transform of the distribution of shift parameters Aco. R Et) reduces to cos (Aco Et) when E and B are parallel and to a Bessel function Jo(AcoEt) when E and B are perpendicular. Ideally, the measurement would best be done by noting those values of Ex which make R Ex) zero, but this is difficult because of inhomogeneous broadening. So Mims and Peisach (1976) expressed their results in terms of a parameter... 

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