The Delayed-Neutron Fraction—Neutron Lifetime Ratio in a TRIGA Reactor from Noise Analysis

The power level fluctuations of the TRIGA Mark II reactor at Otaniemi, Finland have been measured at a power of 3 W. A compensated ionization chamber was used and the signal was analyzed by utilizing a filtering technique. A simple theoretical model for the power spectral density associated with the neutron noise was fitted to the experimental results in the frequency range 4 to 400 cps by the least-squares sum method. Calculations were made on a digital computer, which gave a β/l-value of 121.4 (units) 1/sec. For a delayed-neutron fraction with β = 0.0073, this implies a prompt-neutron lifetime, l, equal to 60.1 ± 3 μ sec. Noise measurements on TRIGA reactors have not been reported earlier.