Abstract
The hypothesis that seasonal changes in proximity to the Sun cause variation of decay constants at permille level has been tested for radionuclides disintegrating through electron capture and beta plus decay. Activity measurements of 22Na, 54Mn, 55Fe, 57Co, 65Zn, 82+85Sr, 90Sr, 109Cd, 124Sb, 133Ba, 152Eu, and 207Bi sources were repeated over periods from 200 d up to more than four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and appear attributable to instabilities in the instrumentation and measurement conditions. Oscillations in phase with Earth’s orbital distance to the sun could not be observed within 10−4–10−5 range precision. The most stable activity measurements of β+ and EC decaying sources set an upper limit of 0.006% or less to the amplitude of annual oscillations in the decay rate. There are no apparent indications for systematic oscillations at a level of weeks or months.
Highlights
This is part III of a series of three papers investigating annual modulations in measured radioactive decay rates and in par ticular the claim that decay constants change at permille level in phase with the seasonal variations in Earth–Sun distance
The decay through β+ and electron capture (EC) processes shows as little variability with respect to annual oscillations as α or β− decay
Good stability was demonstrated for 109Cd (A = 0.015%) and 152Eu (A = 0.01%) measured through ionisation chamber (IC) and γ-ray spectrometry
Summary
This is part III of a series of three papers investigating annual modulations in measured radioactive decay rates and in par ticular the claim that decay constants change at permille level in phase with the seasonal variations in Earth–Sun distance. The most stable activity measurements of α decaying sources set an upper limit of 0.0006% to 0.006% to the amplitude of annual modulations in the decay rate. Claims have been made in the literature that there are violations of the exponential decay law in the shape of seasonal modulations of permille level amplitude. From a metrological point of view, the mere observation of seasonal modulations is insufficient proof of the variability of decay constants as long as instrumental instability cannot be ruled out as a plausible cause of the observed effects [15,16,17]. Square of the Sun–Earth distance, 1/R2, renormalized to an amplitude of 0.15% (which is typical for the magnitude of the effect claimed by Jenkins et al [5])
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