A prototype backscattering neutron time-of-flight spectrometer

Sammanfattning: Measuring neutron energies is an essential task in fusion research. The time-of-flight (TOF) of neutrons moving a known distance can be used to determine these energies. Slower neutrons have longer TOFs for fix flight paths. Neutrons are slowed down when they backscatter. A prototype backscattered neutron TOF spectrometer is constructed so that two detectors D1 and D2 are placed on respective sides of a neutron source. The goal is to measure the TOF of neutrons from the source that reach D1 and backscatter and reach D2. There can, however, be lots of background events that will look like a false backscattering event. Scintillation detectors are used as detectors in the prototype and the neutrons are provided by a californium-252 source. Test results from a first prototype show unsatisfying time-of-flight spectra that are dominated by a large background peak, indicating that further work is required for getting measurement results of time-of-flight of backscattered neutrons. Some aspects of improving the results and the prototype are discussed. Test results from a second prototype do show satisfying spectra, although further work is needed to verify that the difference compared to earlier results is due to backscattered neutrons.