Long-term measurements of 36Cl to investigate potential solar influence on the decay rate

Recently, Jenkins et al. [6] reported on fluctuations in the detected decay events of Cl-36 which were measured with a Geiger-Muller counter. Experimental data of Si-32 measured by means of an end-window gas-flow proportional counter at the Brookhaven National Laboratory show similar periodicity, albeit a different amplitude. Jenkins et al. interpret the fluctuations as evidence of solar influence on the decay rates of beta-decaying radionuclides. In this work, liquid scintillation counting was used to check for potential variations in the Cl-36 decay rates. A custom-built counter with three photomultiplier tubes was used. In contrast to commercial counters, the relevant parameters of our system are well controlled and the discrimination threshold and HV setting can be adjusted and checked. The experimental data were analyzed by means of the triple-to-double coincidence ratio (TDCR) method which is a primary method for activity determination. Thus, our results do not depend on any other standard or reference source. Our data show fluctuations which are by more than one order of magnitude lower than those seen in the experiment using a Geiger-Muller counter. More importantly, no oscillation could be identified. Interestingly, our data overlap in time with those from Jenkins et al. [6]. We do not observe the phase and amplitude as seen by Jenkins and conclude that the fluctuations are not due to solar influence. This also implies that the interpretation by Jenkins et al. is false. (C) 2014 Elsevier B.V. All rights reserved.