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.
The delayed-neutron fraction in a pulsed spallation neutron source
The fraction of delayed neutrons β (with T12 ⪆ 0.25 s) in slow-neutron beams from a 238U pulsed spallation neutron source is 0.0053 for 300 MeV protons. 
 
This appears to be the first measurement of this quantity. The result indicates that, for most classes of measurements, the delayed-neutron background in time-of-flight instruments will be unimportant, and places constraints on the physics description of spallation targets. The measurement was performed at the prototype pulsed spallation neutron source, ZINP-P′, at Argonne National Laboratory.
Pulsed moderator studies using a time focused crystal spectrometer
A technique is reported for measuring the joint time and energy dependence of the rate of emission of slow neutrons emerging from moderators pulsed with fast neutrons. A crystal spectrometer selects neutrons of a given energy and the leakage flux of that energy is examined as a function of time. The spectrometer is arranged to be time-focussed; time resolution is decoupled from energy, spatial and angular resolution. Time-focussing 1. Introduction We report a technique for measuring the joint time and energy dependence of the rate of emission of slow neutrons emerging from moderators pulsed with fast neutrons. A crystal spectrometer is used to select neutrons of a given energy and the leakage flux of that energy is examined as a function of time. The crystal spectrometer is arranged to be time-focussed; time resolution is decoupled from energy, spatial and angular resolution. The time-focussing feature enables measurements to be made using much less intense neutron sources than have been used by earlier workers. Adequate counting rates are obtained by sampling large source area, and large angle and energy widths, while good time resolution is maintained by time focussing. Measurements of the moderator time-energy distributions are required for design of intense pulsed slow neutron sources, and are useful as demanding tests of scattering kernels and neutron transport calculational methods. Fig. 1 illustrates the basic quantity to be