Noise equivalent source for frequency domain measurements from the spontaneous fission of /sup 252/Cf

An experiment was performed to determine the frequency domain noise equivalent source from the spontaneous fission of /sup 252/C. The measurements had maximum frequencies (<50 kHz) much lower than those corresponding to the frequencies associated with emission and detection times of particles from spontaneous fission of /sup 252/Cf. This experiment was performed with a /sup 252/Cf source on one plate of a parallel-plate ionization chamber and two large plastic scintillators (2 x 1 x 0.33 ft) at distances of 75 to 150 cm from the source. This noise equivalent source is important when using the /sup 252/Cf source-driven neutron noise analysis method to determine subcriticality at low values of k/sub eff/ (<<0.8) because at low k/sub eff/ values, fluctuations of the neutron population in the system caused by the varying numbers of neutrons from spontaneous fission of /sup 252/Cf become important. The noise equivalent source for these measurements has been formulated based on the Schottky formalism according to the method of Cohn.