Browsing by Author "Whittal, David Mark"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Energy correlations of prompt neutrons from 252Cf fission
    (1983) Whittal, David Mark; Brooks, F D
    Measurements have been made of the neutron-neutron energy correlations for coincident neutrons emitted in the spontaneous fission of ²⁵²Cf. The hypothesis that cooling of the fission fragments during the cascade evaporation of prompt neutrons affects the energies of successive neutrons in a cascade has been investigated by a comparison of the energy correlations of coincident neutrons from the same fragment with those of coincident neutrons from opposite fragments in the same fission. It is found that the energies of coincident neutrons are posftively correlated and that the correlation coefficient is greater for neutrons from opposite fragments than for neutrons from the same fragment. This provides a sensitive test of the nature of neutron emission in an evaporation cascade. The energy correlations of random (noncoincidental) neutrons have also been investigated and are found to show similar but smaller correlation trends. It is concluded that there is some evidence for the cascade cooling effect on the energies of prompt fission neutrons.
  • Thumbnail Image
    Item
    Open Access
    Quasifree knockout of charged particles from ⁴He with 100 MeV protons
    (1989) Whittal, David Mark; Brooks, F D
    Exclusive measurements have been made of the reactions ⁴He(p,2p ), (p,pd), (p,pt) and (p,ph) at 100 MeV. The primary protons were measured at two angles, 45° and 60°, in coincidence with secondary protons, deuterons, tritons or helions covering a wide range of angles on the opposite side of the beam, from -15° to -90° in plane, and from 0° to 30° out-of-plane. The purpose of the experiment was to explore the validity of the Distorted Wave Impulse Approximation (DWIA) as a description of these quasifree knockout reactions, at all geometries where the knockout cross section is significant. Six particle telescopes, each consisting of two silicon detectors and a NaI detector, were used to measure the coincident particles. The experimental data are presented in the form of energy-sharing distributions, which were generated by projecting the two-dimensional quasifree knockout loci onto the energy axis of the primary proton. The comparison between these energy-sharing distributions and the curves calculated by means of the DWIA is satisfactory for all geometries, except at the most forward secondary angles for the (p,pt) and (p,ph) reactions. It is concluded that the DWIA is an adequate formalism for modelling the quasifree knockout reactions induced by 100 MeV protons on ⁴He. Based on this conclusion, the total contribution of quasifree knockout to the existing inclusive (p,p') spectra has been calculated by integrating the DWIA cross sections over the solid angles of the secondary particles. The spectroscopic factors used were those extracted from the coincidence data. For the (p,pn) reaction, it was assumed that the spectroscopic factors were the same as for (p,2p). It is found that 70 ± 10% of the inclusive continuum yields is attributable to quasifree scattering, with ~30% arising from multiple scattering. At low energies of the scattered proton, the knockout of nucleons constitutes over 90% of the quasifree component, whereas at high energies the knockout of deuterons, tritons and helions dominates the yield. Thus the absence of discernable quasifree peaks in the inclusive spectra is probably due to the cluster knockout contributions filling in the yield at higher energies.