Neutron Scattering - JUWEL - Forschungszentrum Jülich

RESEDA 9
spin flip from up to down or vice versa (with respect to Bz) clarifying the origin of the
naming „π-flip“.
3.2 NRSE signal and setup
A combination of two resonant spin flips as used in NRSE, results in the same final
neutron spin phase as one single NSE precession region (figure 5), assuming double
magnitude of the NSE field compared to Bz: B = 2·Bz . Hereby, the NSE coil length L is
assumed to equal the distance of the NRSE coils.
The phase angle accumulated by the rotating field Brf during the time t=L/v the neutron
spends between the two coils is φ= ωrf t. The total spin phase gained after the neutron
passes through two NRSE coils, separated by the distance L, is φneutron = 2φ as shown in
figure 5.
Figure 5: Schematic of two NRSE coils at distance L, which replace one NSE precession coil. The rotating
field Brf is in resonance to the static field Bz (Bz is not visible in the figure, as it points out of the plane of
drawing). φ= ωrf t is the phase angle accumulated by the rotating field Brf during the time t=L/v the neutron
spends between the two coils. The total spin phase gained after the neutron passes through both coils is
φneutron = 2φ. Note the analogy to classical spin echo: φneutron is equivalent to the spin phase accumulated
in a coil with length L and the static magnetic field B = 2⋄Bz .
A complete NRSE setup consists, consequently, of four NRSE coils, two in each
spectrometer arm, with the flight paths in-between (figure 6).
Figure 6: Schematic setup of a complete NRSE setup consisting of four NRSE coils, two in each
spectrometer arm in front of and behind the sample. The static magnetic fields Bz are directed in the same
direction in the same spectrometer arm, but in opposite direction with respect to the two arms. As in NSE, a
NRSE setup is completed by a polariser in front of the precession regions, and a spin analyser placed
behind the second precession region.