Tests of a prototype pulsed thermal neutron source

Abstract

In the pulsed neutron experiments, an increase of the thermal neutron flux is necessary when weakly-moderating materials are measured as sole samples, without an extra moderator. A prototype of the pulsed thermal neutron source has been designed and constructed at the 14 MeV pulsed neutron generator. The moderator array is made of small paraffin cells (1.8x1.8x4.4 cm3 ) separated with a Cd layers which prevent the thermal neutron diffusion between the cells. The width of the array has been optimized concerning the efficiency of the slowing down the 14 Mev neutrons to the thermal energies. The decay of the thermal neutron flux from such a moderator is very rapid. Test measurements of the presented pulsed thermal neutron source are described. The decay constant of the thermal neutron flux is equal to about 92 000 s-1. The repetition time and the duration of the pulses are controlled by the parameters of the primary fast neutron source.