On the interpretation of annual oscillations in 32Si and 36Cl decay rate measurements

The Si-32 decay rate measurement data of Alburger et al. obtained in 1982-1986 at Brookhaven National Laboratory have been presented repeatedly as evidence for solar neutrino-induced beta decay. The count rates show an annual sinusoidal oscillation of about 0.1% amplitude and maximum at February-March. Several authors have claimed that the annual oscillations could not be explained by environmental influences on the set-up, and they questioned the invariability of the decay constant. They hypothesised a correlation with changes in the solar neutrino flux due to annual variations in the Earth-Sun distance, in spite of an obvious mismatch in amplitude and phase. In this work, environmental conditions at the time of the experiment are presented. The Si-32 decay rate measurements appear to be inversely correlated with the dew point in a nearby weather station. Susceptibility of the detection set-up to local temperature and humidity conditions is a likely cause of the observed instabilities in the measured decay rates. Similar conclusions apply to Cl-36 decay rates measured at Ohio State University in 2005-2012.

Automated summary

Si-32 decay rate measurements show annual oscillations possibly related to changes in solar neutrino flux, but environmental changes and local weather conditions may cause instability in measured decay rates.