Double-difference method to improve the resolution of an eV neutron spectrometer

Epithermal (eV) neutron spectrometers designed to measure the dynamic properties of condensed matter have been developed at several pulsed neutron sources, using nuclear resonances to define neutron energy. The energy resolution of such a spectrometer is limited by the width of the nuclear resonance. The paper describes how a linear combination of measurements with two thicknesses of foils of the resonance material yields better energy resolution than either foil alone. With proper selection of foil thicknesses, there is no penalty in counting statistics to obtain the improved resolution. The double-difference method also suppresses the wings of the resonance and yields a function with a finite second moment so that uncertainties may be properly propagated. (orig.)