Novel measuring methods in neutron interferometry

Perfect crystal interferometry is becoming a standard tool for precise measurements of coherent scattering lengths. So far accuracy was limited by the resolution achieved with the determination of the wavelength and the wavelength distribution. The newly tested nondispersive sample arrangement avoids this shortcoming because the phase shift becomes independent of the wavelength. Arbitrarily shaped samples can be measured by an adapted Christiansen filter method, where the scattering length density of the powdered sample is matched to the scattering length density of a surrounding liquid. The following values for the bound coherent scattering lengths were determined: b_c(Bi) = 8.5165(62) fm by the standard method, b_c(Bi) = 8.521(4) fm by the nondispersive method and b_c(Si) = 4.157(3) fm by the Christiansen filter method. A phase sensitivity of 2.2 × 10⁻⁵ was achieved, which could easily be increased to a level of 10⁻⁶.