Gregory Rech, University of California at Berkeley / Lawrence Berkeley National Laboratory

Title: Search for Environmental Influences on the ⁷Be Decay Rate

Authors: G. Rech, E. Norman, M.R. Dragowsky, Y.D. Chan, M.C. Perillo Isaac, R.-M. Larimer (Lawrence Berkeley National Laboratory, University of California, Berkeley)

Abstract: ⁷Be plays an important role in the generation of solar neutrinos.  Because ⁷Be decays via electron capture, its half-life depends on the electron density at the nucleus.  Two groups have recently reported observations of variations of ~1% in the decay rate of ⁷Be as a function of the physical environment in which the ⁷Be is located.  In order to test this idea, we measured the half-life in four different host materials.  Samples of ⁷Be in graphite, boron nitride, tantalum and gold were produced at LBNL's 88" Cyclotron.  Each ⁷Be sample was sealed and packaged together with a ¹³³Ba reference source.  These composite sources were individually g-counted in 1-day time bins periodically over 4 months using a 110-cm³ coaxial germanium detector.  In order to reduce systematic effects from variations in detector or electronic performance, the ⁷Be half-life was determined by comparing the numbers of 478-keV ⁷Be and 356-keV ¹³³Ba gamma rays observed from each sample.  Results from the analysis of this data will be presented.