Here are two papers which find no evidence of periodic fluctuations in decay rates. Both have been published in journals since being uploaded
to arxiv.org Harry http://arxiv.org/abs/0809.4248 Searching for modifications to the exponential radioactive decay law with the Cassini spacecraft Authors: Peter S. Cooper (Submitted on 24 Sep 2008) Abstract: Data from the power output of the radioisotope thermoelectric generators aboard the Cassini spacecraft are used to test the conjecture that small deviations observed in terrestrial measurements of the exponential radioactive decay law are correlated with the Earth-Sun distance. No significant deviations from exponential decay are observed over a range of 0.7 - 1.6 A.U. A 90% Cl upper limit of 0.84 x 10^-4 is set on a term in the decay rate of Pu-238 proportional to 1/R^2 and 0.99 x 10^-4 for a term proportional to 1/R. http://arxiv.org/abs/0810.3265 Evidence against correlations between nuclear decay rates and Earth-Sun distance Authors: Eric B. Norman, Edgardo Browne, Howard A. Shugart, Tenzing H. Joshi, Richard B. Firestone (Submitted on 17 Oct 2008) Abstract: We have reexamined our previously published data to search for evidence of correlations between the rates for the alpha, beta-minus, beta-plus, and electron-capture decays of 22Na, 44Ti, 108Agm, 121Snm, 133Ba, and 241Am and the Earth-Sun distance. We find no evidence for such correlations and set limits on the possible amplitudes of such correlations substantially smaller than those observed in previous experiments.
