Measurement of the delayed neutron fraction and correction of small angle scattering data from a pulsed spallation source
Abstract The fraction of delayed neutrons in a moderated beam from the enriched uranium, pulsed spallation source at the intense pulsed neutron source at Argonne National Laboratory has been measured and found to be 0.0283 for 450-MeV protons. Delayed neutrons produce a sample-dependent background in time-of-flight instruments. Because of the distribution of neutron wavelengths in the prompt pulse, the significance of the delayed neutron contribution to the observed scattering profile is strongly dependent on the wavelength and therefore on the magnitude of the momentum transfer. This effect is demonstrated, and a general correction procedure in current use for small angle neutron scattering data is described.
Simulated Fast Neutron Instrument Backgrounds at a MW Spallation Source
Like every megaproject, the European Spallation Source (ESS) currently under construction in Lund, Sweden, has had to make a number of inevitable compromises to remain within budget and on schedule. Some of these compromises carry technical consequences with a potential impact on the operational characteristics of the facility and the neutron scattering instruments in particular. In order to prepare for operation of the facility, it is timely to consider again the sub-jects of instrument backgrounds and shielding from the project design phase. The expected ranges of instrument backgrounds, and the relative strengths of each contributor, are estimated using multiple physics simulations. These are compared with other leading spallation sources. Finally, several suggestions are given to reduce the background contributions in each case, should they prove to be dominant in practice when the commissioning phase of the facility begins.
Inverted geometry TOF spectrometer at the ZING-P pulsed neutron source prototype
Abstract A neutron inelastic scattering spectrometer has been constructed and operated at the spallation pulsed neutron source prototype (ZING-P) at Argonne National Laboratory. The spectrometer operates in the inverted geometry mode with a pulsed polychromatic incident beam and a focused crystal analyzer in the scattered beam. High efficiency is achieved by the large angular acceptance of the analyzer unit. The instrument is useful for the measurement of spectra in the range 0–200 meV in cases where the value of the momentum transfer is not crucial.