Experimental investigation of variance-to-mean formula for periodic and pulsed neutron source

A series of experiments was carried out by using the Kyoto University Critical Assembly and a pulsed neutron generator attached. The experiments were intended to investigate a variance-to-mean technique for measuring the prompt neutron decay constant α of the subcritical reactor system that was driven by the periodic and pulsed neutron source. As the results, it was confirmed that the α value measured by the present technique agreed with a reference value evaluated by the pulsed neutron technique. Furthermore, it was demonstrated that the present technique was available to measure the α value even when the product of α and the repetition period of pulsed neutrons was smaller than unity. Since measurement of α by the pulsed neutron technique is generally difficult under such conditions, it was concluded that the present technique was convenient for measuring the α value.