, Volume 337, Issue 1, pp 39-45
Date: 09 Sep 2011

Solar influence on nuclear decay rates: constraints from the MESSENGER mission

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We have analyzed 137Cs decay data, obtained from a small sample onboard the MESSENGER spacecraft en route to Mercury, with the aim of setting limits on a possible correlation between nuclear decay rates and solar activity. Such a correlation has been suggested recently on the basis of data from 54Mn decay during the solar flare of 13 December 2006, and by indications of an annual and other periodic variations in the decay rates of 32Si, 36Cl, and 226Ra. Data from five measurements of the 137Cs count rate over a period of approximately 5.4 years have been fit to a formula which accounts for the usual exponential decrease in count rate over time, along with the addition of a theoretical solar contribution varying with MESSENGER-Sun separation. The indication of solar influence is then characterized by a non-zero value of the calculated parameter ξ, and we find ξ=(2.8±8.1)×10−3 for 137Cs. A simulation of the increased data that can hypothetically be expected following Mercury orbit insertion on 18 March 2011 suggests that the anticipated improvement in the determination of ξ could reveal a non-zero value of ξ if present at a level consistent with other data.