A Simple Way to Overcome the Shortage of $^{3}\rm {He}$ Detectors in the IPEN/MB-01 Nuclear Reactor

In order to overcome the shortage of
³
He detectors for subcritical experiments in the IPEN/MB-01 reactor, some experiments were performed employing less sensitive detectors, such as BF
₃
, and a logic input module, which sums the counts from different detectors. Through microscopic and macroscopic neutron noise technique, it was possible to obtain, respectively, Rossi-α distribution and Auto Power Spectral Densities (APSD) for each detector configuration and various subcritical levels, and the prompt neutron decay constant (α) was extracted through a least squares procedure. In addition, Cross Power Spectral Densities (CPSD) were acquired for different types of detectors and the correlation among those detectors was confirmed. It was also observed that there was no loss of correlation among the neutron pulses, and therefore, the CPSD curves demonstrated the presence of correlated events. The α parameter was used as an indicator for the comparison of the results and for the quality of the experimental data. The obtained values demonstrate that the sum of counts technique does not present loss of information (correlated neutrons) even for different models and types of detectors, suggesting that the technique may be employed in neutron noise measurements for subcritical reactivity.