Test of nuclear decay rate variation due to an antineutrino flux

Background: Unexplained variations of the decay rate parameter for weak interaction decays such as beta(+/-) decay, electron capture, as well as strong interaction a decay have been reported. Because these variations have been presented by a number of groups, at various locations, using various types of detectors, different isotopes, and over extended periods of time, some researchers have interpreted the source of these variations as not from ambient environmental factors such as temperature, pressure, and humidity but via an unexplained fundamental interaction. Purpose: The state of decay rate parameter variations experiments is reviewed, and the reported results are placed into a common comparable context by defining a phenomenological cross section. Then we make decay parameter measurements as a function of time at the level of 10(-5) in the presences of an antineutrino flux with an on-off cycle time of approximate to 30 days. This level of precision requires a detailed understanding of both systematic and statistical errors; otherwise, systematic errors in the measurement may mimic the decay events of fundamental interactions. Methods: The experiment searched for variation of the Mn-54(25), e(-) capture decay rate parameter and Cs-137(55), beta(-) decay rate parameter both to a level of precision of 1 part in approximate to 10(5) by comparing the difference between the decay rate in the presence of an antineutrino flux approximate to 3 x 10(12) (nu) over bar cm(-2) s(-1) and no flux measurements. The experiment was located 6.53 m from the reactor core of the High Flux Isotope Reactor at the Oak Ridge National Laboratory. Two weak interaction decays, one via electron capture and the other via beta(-) decay, were selected because the final state and the time reverse state each contain a neutrino and antineutrino, covering arguments that the antineutrino flux may interact differently or not at all in one of the cases. Results: The gamma spectra from both decays were collected and analyzed independently. The measured variation in the decay rate parameters are found to be delta lambda/lambda = (0.034 +/- 1.38) x 10(-5) for Mn-54(25) and delta lambda/lambda = (0.67 +/- 1.56) x 10(-5) for Cs-137(55). These results are consistent with no measurable decay rate parameter variation due to an antineutrino flux, yielding a 68% confidence level upper limit sensitivity for Mn-54(25) delta lambda/lambda <= 1.31 x 10(-5) or sigma <= 1.29 x 10(-25) cm(2) in cross section and for Cs-13(7)55 delta lambda/lambda <= 2.23 x 10(-5) or sigma <= 5.69 x 10(-27) cm(2). Conclusions: The cross-section upper limit obtained in these null or no observable effect measurements are approximate to 10(4) times more sensitive than past experiments reporting positive results in Mn-54 and Cs-137.