On the claim of modulations in 36Cl beta decay and their association with solar rotation

Recently, claims were made by Sturrock et al. (Astropart. Phys.42, 62, 2013), Sturrock, Fischbach, and Scargle (Solar Phys.291, 3467, 2016; arXiv , 2017) that beta decay can be induced by interaction of the nucleus with solar neutrinos and that cyclic modulations in decay rates are indicative of the dynamics of the solar interior. Transient modulations in residuals from a purely exponential decay curve were observed at frequencies near \(11~\mbox{a}^{-1}\) and \(12.7~\mbox{a}^{-1}\) in repeated activity measurements of a 36Cl source by Alburger, Harbottle, and Norton (Earth Planet Sci. Lett.78, 168, 1986) at Brookhaven National Laboratory in a period from 1984 to 1985. Sturrock et al. have speculatively associated them with rotational influence on the solar neutrino flux. In this work, more accurate 36Cl decay-rate measurements – performed at the Physikalisch-Technische Bundesanstalt Braunschweig in the period 2010 – 2013 by means of the triple-to-double coincidence ratio measurement technique – are scrutinised. The residuals from an exponential decay curve were analysed by a weighted Lomb–Scargle periodogram. The existence of modulations in the frequency range between \(0.2~\mbox{a}^{-1}\) and \(20~\mbox{a}^{-1}\) could be excluded down to an amplitude of about 0.0016%. The invariability of the 36Cl decay constant contradicts the speculations made about the deep solar interior on the basis of instabilities in former activity measurements.