Unexplained periodic fluctuations in the decay rates of 32 Si and 226 Ra have been reported by groups at Brookhaven National Laboratory ( 32 Si), and at the Physikalisch-TechnischeBundesandstalt in Germany ( 226 Ra). We show from an analysis of the raw data in these experiments that the observed fluctuations are strongly correlated in time, not only with each other, but also with the distance between the Earth and the Sun. Some implications of these results are also discussed, including the suggestion that discrepancies in published half-life determinations for these and other nuclides may be attributable in part to differences in solar activity during the course of the various experiments, or to seasonal variations in fundamental constants. Following the discovery of radioactivity by Becquerel in 1896 [1] an intense effort was mounted to ascertain whether the decay rates of nuclides could be affected by external influences including temperature, pressure, chemical composition, concentration, and magnetic fields. By 1930, Rutherford, Chadwick, and Ellis [2, p. 167] concluded that "The rate of transformation of an element has been found to be a constant under all conditions." (For decays resulting from K-capture, or for beta-decays in strong ambient electromagnetic fields, the situation is slightly more complicated, since these decays are influenced by the electron wave functions which can be affected by external pressure or fields [3,4,5].) For 32 Si and 226 Ra, which decay by beta-and alpha-emission, respectively, fluctuations in the counting rates (in the absence of strong external electromagnetic fields) should thus be uncorrelated with any external time-dependent signal, as well as with each other. In what follows we show that neither of these expectations is realized in data we have analyzed for 32 Si and 226 Ra, thus suggesting that these decays are in fact being modulated by an external influence.Between 1982 and 1986, Alburger, et al. [6] measured the half-life of 32 Si at Brookhaven National Laboratory (BNL) via a direct measurement of the counting rate as a function of time. If N (t) denotes the number of surviving atoms starting from an initial population N 0 at t = 0, then the familiar exponential decay law, N (t) = N 0 e −λt , leads toṄ ≡ dN/dt = −λN 0 e −λt where λ = ln(2)/T 1/2 . A plot of ln Ṅ (t) as a function of time is then a straight line whose slope is λ, which then gives the half-life T 1/2 . At the time this experiment was initiated, the 32 Si half-life was believed to be in the range of 60 T 1/2 700 yr, and hence a multiyear counting experiment was needed to obtain a measureable slope. As in other counting experiments, the counting rate for 32 Si was continually monitored in the same detector against a long-lived comparison standard, which in the BNL experiment was 36 Cl (T 1/2 =301,000 yr). Since the fractional change in the 36 Cl counting rate over the four year duration of the experiment was only O(10 −5 ), which was considerably smaller than the overall uncertainty of the final res...

This paper presents an overview of recent research dealing with the question of whether nuclear decay rates (or half-lives) are time-independent constants of nature, as opposed to being parameters which can be altered by an external perturbation. If the latter is the case, this may imply the existence of some new interaction(s) which would be responsible for any observed time variation. Interest in this question has been renewed recently by evidence for a correlation between nuclear decay rates and Earth-Sun distance, and by the observation of a dip in the decay rate for 54 Mn coincident in time with the solar flare of 2006 December 13. We discuss these observations in detail, along with other hints in the literature for time-varying decay parameters, in the framework of a general phenomenology that we develop. One consequence of this phenomenology is that it is possible for different experimental groups to infer discrepant (yet technically correct) results for a half-life depending on where and how their data were taken and analyzed. A considerable amount of attention is devoted to possible mechanisms which might give rise to the reported effects, including fluctuations in the flux of solar neutrinos, and possible variations in the magnitudes of fundamental parameters, such as the fine structure constant and the electron-to-proton mass ratio. We also discuss ongoing and future experiments, along with some implications of our work for cancer treatments, 14 C dating, and for the possibility of detecting the relic neutrino background.

Evidence for an anomalous annual periodicity in certain nuclear-decay data has led to speculation on a possible solar influence on nuclear processes. We have recently analyzed data concerning the decay rates of 36 Cl and 32 Si, acquired at the Brookhaven National Laboratory (BNL), to search for evidence that might be indicative of a process involving 252 P.A. Sturrock et al. solar rotation. Smoothing of the power spectrum by weighted-running-mean analysis leads to a significant peak at frequency 11.18 year −1 , which is lower than the equatorial synodic rotation rates of the convection and radiative zones. This article concerns measurements of the decay rates of 226 Ra acquired at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. We find that a similar (but not identical) analysis yields a significant peak in the PTB dataset at frequency 11.21 year −1 , and a peak in the BNL dataset at 11.25 year −1 . The change in the BNL result is not significant, since the uncertainties in the BNL and PTB analyses are estimated to be 0.13 year −1 and 0.07 year −1 , respectively. Combining the two running means by forming the joint power statistic leads to a highly significant peak at frequency 11.23 year −1 . We will briefly comment on the possible implications of these results for solar physics and for particle physics.

We provide the results from a spectral analysis of nuclear decay data displaying annually varying periodic fluctuations. The analyzed data were obtained from three distinct data sets: 32 Si and 36 Cl decays reported by an experiment performed at the Brookhaven National Laboratory (BNL), 56 Mn decay reported by the Children's Nutrition Research Center (CNRC), but also performed at BNL, and 226 Ra decay reported by an experiment performed at the Physikalisch-Technische-Bundesanstalt (PTB) in Germany. All three data sets exhibit the same primary frequency mode consisting of an annual period. Additional spectral comparisons of the data to local ambient temperature, atmospheric pressure, relative humidity, Earth-Sun distance, and their reciprocals were performed. No common phases were found between the factors investigated and those exhibited by the nuclear decay data. This suggests that either a combination of factors was responsible, or that, if it was a single factor, its effects on the decay rate experiments are not a direct synchronous modulation. We conclude that the annual periodicity in these data sets is a real effect, but that further study involving additional carefully controlled experiments will be needed to establish its origin.

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