Power spectrum analysis of BNL decay rate

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Astroparticle Physics 34,2 (2010) 121-127;


Evidence for an anomalous annual periodicity in certain nuclear decay data has led to speculation concerning a possible solar influence on nuclear processes. As a test of this hypothesis, we here search for evidence in decay data that might be indicative of a process involving solar rotation, focusing on data for Si-32 and Cl-36 decay rates acquired at the Brookhaven National Laboratory. Examination of the power spectrum over a range of frequencies (10-15 year(-1)) appropriate for solar synodic rotation rates reveals several periodicities, the most prominent being one at 11.18 year(-1) with power 20.76. We evaluate the significance of this peak in terms of the false-alarm probability, by means of the shuffle test, and also by means of a new test (the "shake" test) that involves small random time displacements. The last two tests are the more robust, and indicate that the peak at 11.18 year(-1) would arise by chance only once out of about 10(7) trials. However, the fact that there are several peaks in the rotational search band suggests that modulation of the count rate involves several low-Q oscillations rather than a single high-Q oscillation, possibly indicative of a partly stochastic process. To pursue this possibility, we investigate the running-mean of the power spectrum, and identify a major peak at 11.93 year(-1) with peak running-mean power 4.08. Application of the shuffle test indicates that there is less than one chance in 10(11) of finding by chance a value as large as 4.08. Application of the shake test lads to a more restrictive result that there is less than one chance in 10(15) of finding by chance a value as large as 4.08. We find that there is notable agreement in the running-mean power spectra in the rotational search band formed from BNL data and from ACRIM total solar irradiance data. Since rotation rate estimates derived from irradiance data have been found to be closely related to rotation rate estimates derived from low-energy solar neutrino data, this result supports the recent conjecture that solar neutrinos may be responsible for variations in nuclear decay rates. We also carry out a similar comparison with local temperature measurements, but find no similarity between power spectra formed from BNL measurements and from local temperature measurements. (C) 2010 Elsevier B.V. All rights reserved.

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