Subcritical Reactivity from Polarity Correlation

A generalization of Pacilio's method has been developed for utilizing two detectors to investigate reactor noise. The method requires only the measurement of the polarity of the detector output-current as compared with its average value, and therefore is of use in reactor systems with appreciable subcritical power. The modification extends the theory to the case in which the covariance can exceed unity. A unique bivariate negative binomial distribution is proposed for describing the correlated detectors, and a formula for the covariance-to-mean ratio is developed in terms of the polarity correlations between the detectors. From the ratio, the subcritical reactivity of the system can be determined.