Experimental demonstration of the finite measurement time effect on the Feynman- technique

The reactivity of a subcritical system is determined by fitting two different theoretical models to a measured Feynman-cr curve. The first model is the expression usually found in the literature, which can be shown to be the epectation value of the experimental quality if the measurement time is infinite. The second model is a new expression which is the expectation value of the experimental quantity for a finite measurement time. The reactivity inferred with the new model is seen to be independent of the length of the fitting interval, whereas the reactivity inferred with the conventional model is seen to vary. This difference demonstrtes the effect of the finite measurement time. As a reference, the reactivity is also measured with the pulsed-neutron source method. It is seen to be in good agreement with the reactivity obtined with the Feynman-a technique when the new expression is applied