A Study on the Zero-Probability Method
T. Kobayashi · Journal of Nuclear Science and Technology · 1968
Let us consider the probabilities p(n,t) and pm(n,t) Here, p(n,t) is the probability that exactly n neutrons are found in the reactor at time t>0 when a neutron had been injected at t=0, and pm(n,t) the probability that a neutron detector placed in the reactor counts exactly m neutrons during a lime interval (0,t) and exactly n neutrons are found at time t when a neutron had been injected at t=0. By formulating p(n,t) and pm(n,t) in terms of last collision probabilities, linear partial differential equations for probability generating functions of p(n,t) and of pm(n,t) have been derived. After solving these equations, the theory of zero-probability method is discussed. And it is shown that the probability P0(t) of recording no count during a time interval t is a function of a decay time constant α of prompt neutron chains and t. Moreover, an experiment has been carried out on an assembly containing slightly enriched uranium. Rossi-α measurements and pulsed neutron measurements have also been made for verification. The parameter α measured by the zero-probability method does not agree well with those by the other methods.