Collimation effect of water collimator to D-D and D-T neutrons

A study of a water collimator is performed for 5-cm and 10-cm daim. cylindrical collimators located in a 100-cm water shield. A point neutron source of D-D or D-T reactions is located at the entrance to the collimator. Results of the Monte Carlo simulation are analyzed as reference data. Two parameters are proposed to measure the collimation effects, i.e. scattered neutron flux on the axis of the collimator and the width of the plateau observed in the scattered flux profile. The flux on the axis is analyzed by a single-albedo-scattering model, while the width of the plateau is represented by a single-scattering model in the shied. The flux on the axis is nearly proportional to the collimator radius. The axial profile of the on-axis flux is closely approximated with an imaginary source assumed at the center of the collimator. The imaginary source reproduces the width of the plateau in the radial profile of the scattered flux. (author)