Spin-Echo Three-Axis Spectrometer: A Reality

Abstract

Because of the stringent requirements on the magnetic precession fields this technique has taken a long implementation time. The solution of the homogeneity and of the stray-field problem is the Optimal Field Shape (OFS) which allows the use of wide and divergent neutron beams. On the ISSP thermal three-axis spectrometer equipped with OFS coils relative energy resolutions of l0⁻⁵ have now been obtained. At the ILL the implementation of super conducting OFS coils is expected to yield 10⁻⁶. The quality of the spin-echo polarisation and the spin echo phase are independent of the scattering angle. A further possibility of TASSE (Three Axis Spectrometer with Spin Echo) which has been developed and is to be tested, is complete phonon focusing, that is matching of both slope and curvature of the constant spin echo phase surface to those of the dispersion surface of the excitation, the lifetime of which is to be determined.