Generalized Lomb-Scargle analysis of $\rm{^{36}Cl}$ decay rate measurements at PTB and BNL

Abstract: Recently, Pomme et al did an analysis of $\rm{^{36}Cl} $ 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 Brookehaven 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. All our analysis codes and datasets have been made publicly available.