A New Neutron-Flux Detection Method for Fission Chamber Counting Systems

A new counting method for a detection system using a fission chamber placed under high neutronflux is presented. This method is based on the fact that pile-up of pulses delivered by the fission chamber produces a linear relation on log-log scale between the neutron-flux and the threshold voltage of an amplitude discriminator, when a count-rate of output pulses of the discriminator is maintained at a constant value. The fact has been verified by a theoretical approach using a simple model. A counting system with a negative feedback loop has been constructed to carry out this constant count-rate amplitude discrimination. Experimental results obtained by utilizing a small fast reactor show that the system can cover a wide range of the reactor power.