Beta decay analysis using Lombscargle periodogram for PTB and BNL datasets arXiv:1912.06970
Recently Pomme et al. did an analysis of Cl(36) radioactive decay data from measurements at the Physikalisch-Technische Bundesanstalt (PTB), in order to verify the claims by Sturrock and collaborators of an influence on beta-decay rates measured at Brookhaven National Lab (BNL) due to the rotation-induced modulation of the solar neutrino flux. Their analysis excluded any sinusoidal modulations in the frequency range from 0.2-20/year. We carry out an independent analysis of the same PTB and BNL data, using the generalized Lomb-Scargle periodogram to look for any statistically significant peaks in the range from 0 to 14 per year, and by evaluating the significance of every peak using multiple methods. Our results for the PTB data are in agreement with those by Pomme et al. For BNL data, we do find peaks at some of the same frequencies as Sturrock et al., but the significance is much lower.
The original PTB dataset~\cite{Pomme} showing the $\ce{^{36}Cl}$ decays. The best-fit line has a slope equal to $9.36 \times 10^{-5}$ and $y$-intercept is equal to 0.81.
Residuals in the PTB dataset after applying the linear correction (outlined in Fig.~\ref{Figi}). The uncertainty for each data point is $0.009$%.
Relative difference from the mean value of measured $\ce{^{36}Cl}$ at the BNL (applying $0.13%$ uncertainty on individual data)~\cite{BNL}.
Weighted L–S periodograms of $ \ce{^{36}Cl} $ decay rate data measured at the BNL (top panel) for frequencies in the range 0 - 14 $ a^{-1}$). The bottom panel shows the Z-scores greater than zero (obtained from $p$-value calculated via the Baluev method) for different frequencies.
Weighted L–S periodograms of $ \ce{^{36}Cl} $ decay rate data measured at the PTB for frequencies in the range 0 - 14 $ a^{-1}$). The Z-scores are negligible and not shown here.