Improving analysis and detection of neutrons at high energies
Neutrons are elementary atomic particles with no charge and mass almost equal to that of a proton. When reaching high energies, these particles interact with atomic nucleuses and their scattering characteristics constitute a valuable tool for condensed matter research studies. In particular, pulsed neutron sources feature distinctive spectral characteristics, such as width of energy peaks that allow more accurate spectroscopic studies in condensed matter. Conventionally, the most efficient method of energy analysis exploits nuclear resonance absorption. Uranium foils display nuclear resonance that absorb neutrons strongly over a narrow energy range and the scattering technique consists of cycling the foil in and out of the scattered neutron beam. Thereby, two measurements are taken, one with the foil between sample and detector and one with the foil removed. Their difference provides a measurement of the intensity of neutrons scattered from the sample with a final energy. Focusing on improving the energy resolution of neutrons in the eV energy range, this project resulted into two important enhancements of the conventional method. The first consists of cooling of the uranium analyser foil because uranium resonance at room temperature is highly modified due to thermal motions leading to inaccurate results. The second involves using the double difference technique that consists of taking three measurements with no foil, and with two uranium foils with different thickness and transmissions. This leads to a more precise data analysis with a factor of almost two-fold improvement to the derived resolution.
