Experimental Demonstration Of Neutron Multiplicity Counting In The Current Mode Of Fission Chambers

As we have presented at several journal papers and previous INMM conferences, one can extract the factorial moments of traditional multiplicity counting from the two- and three-point temporal distributions of the current mode signals of fission detectors. Specifically, it was shown that the three low order moments (mean value, covariance function and bicovariance function) of the signals form simple linear relationships with the singles doubles and triples rates. A major advantage of this approach over the traditional method is that the current mode operation is inherently free from dead time introduced by a counting system. To demonstrate the practical applicability of the proposed method, an experiment was designed and performed at the KUCA facility of the Kyoto University. Four fission chambers were used to detect neutrons emitted from a combination of Cf-252 and U-235 samples. Optimal measurement arrangements were chosen based on simulations. An FPGA based fast data acquisition system was assembled to record the voltage signals of the detectors with a sampling rate up to 100 MHz. The times of individual counts were also registered for performing a reference analysis with the traditional pulse counting approach. The moments of the recorded voltage signals were determined, from which the singles and doubles rates were calculated. The applicability of the new method was assessed by comparing these results with those obtained from the counting statistics. The results are promising and prove the feasibility of the new method possibly opening new opportunities for multiplicity counting of high intensity samples and the application of fission chambers in such measurements.