High precision measurement of the half-life of the 391.6 keV metastable level in 239Pu
Abstract
Materials selection for rare event physics requires high performance detectors and customized analyses. In this context a novel β-γ detection system, comprised of a liquid scintillator in coincidence with a HPGe, was developed with the main purpose of studying ultra trace contamination of uranium, thorium and potassium in liquid samples. In the search for 238U contaminations through neutron activation analysis, since the activation product 239Np decays to a relatively long-lived isomeric state of 239Pu, it is possible to perform a time selection of these events obtaining a strong background suppression. Investigating the time distribution of the coincidences between the β- decay of 239Np and the delayed events following the de-excitation of the 239Pu isomeric level at 391.6 keV, a precision measurement of the half-life of this level was conducted. The half-life of the 391.6 keV 239Pu level resulted 190.2 0.2 ns, thus increasing the precision by about a factor of 20 over previous measurements.
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