Measurement of the Thermal-Neutron Extrapolation Length in a Pulsed Water System

As part of a comprehensive project to investigate the validity of pulsed-neutron measurements in small systems, we have measured the extrapolation length in a pulsed light-water system with B² = 0.11/cm². Space- and time-dependent flux distributions were obtained with a miniature fission chamber and were analyzed by least-squares techniques. Special attention was paid to the extraction of the fundamental mode and to the overall internal consistency of the results. The thermal-neutron extrapolation length, corrected to 20°C, was found to be 0.300 ± 0.015 cm.