Flicker-noise fluctuations in α-radioactive decay

Abstract

Counting statistics of α particles from three sources, one containing 241Am; one containing 239Pu, 241Am, and 244Cu; and a source containing 148Gd, were determined over periods of 1–4000 min. In particular, the two-sample variance or Allan variance was determined for many sample runs. According to a recent theorem, there is a unique relation between the particle-flux spectral noise density and the Allan variance. It was found that for small counting periods, the statistics were Poissonian, corresponding to shot noise of the particle flux. For long periods[Formula: see text], the counting statistics were found to be non-Poissonian, indicating the presence of 1/f noise and (or) Lorentzian noise.The 1/f noise gave flicker floors of (0.5–0.7) × 10−7 for 239Pu, (1.0–1.3) × 10−7 for 241Am, and 3.0 × 10−7 for 244Cm. The Lorentzians were not reproducible in different runs and are probably associated with chemical oxidation-reduction rate processes in the source. The 1/f noise is likely inherent in the process of α-particle decay, indicating that the classical picture of alpha decay as a Poisson process is incomplete. Some forms of quantum 1/f noise associated with the tunnel-emission process are briefly discussed.