Abstract
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.
Highlights
The validity of the exponential decay law has been questioned in a series of recent articles by authors claiming that periodical oscillations in repeated radioactivity measurements are indicative of variability in the decay constants, whereas others have refuted these claims on metrological and theoretical grounds
An overview of the discussion can be found in articles by Pommé et al (2016, 2017a, 2017b, 2017c, 2018), which contradict the hypothesis of variability of decay constants – endorsing the validity of the exponential decay law – on the basis of a large suite of accurate decay-rate measurements provided by national radionuclide metrology institutes from all over the world
The precise 36Cl decay-rate measurements performed at the Physikalisch-Technische Bundesanstalt (PTB) were investigated for cyclic deviations from exponential decay at frequencies between 0.2 a−1 and 20 a−1
Summary
The validity of the exponential decay law has been questioned in a series of recent articles by authors claiming that periodical oscillations in repeated radioactivity measurements are indicative of variability in the decay constants, whereas others have refuted these claims on metrological and theoretical grounds. Claim to have observed modulations in beta decay with frequencies of the order of 11 – 13 a−1, which they speculatively associate with internal solar rotation They observed a prominent ‘transient cycle’ of 12.7 a−1 (28.76 days period, 0.07% amplitude) in spectrograms formed from countings of 36Cl and 32Si decays in a gasflow proportional counter at BNL (Alburger, Harbottle, and Norton, 1986) and found them indicative of the synodic rotation rate of the radiative zone of the Sun, since it matches its helioseismologically determined period of 28.7 days (Schou et al, 1998; Komm et al, 2003). They suggested that ‘a reasonable search band for the synodic modulation of beta-decay rates would seem to be 9 – 14 a−1, corresponding to periods in the range of 26 – 41 days’
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