High precision measurement of the half-life of the 391.6 keV metastable level in 239Pu

TL;DR

This paper reports a highly precise measurement of the half-life of the 391.6 keV metastable level in 239Pu, achieved through a novel beta-gamma coincidence detection system, significantly improving previous accuracy.

Contribution

The study introduces a new detection system and methodology that enhances the precision of measuring the 239Pu metastable level's half-life by a factor of 20.

Findings

Half-life of 239Pu 391.6 keV level measured as 190.2 ± 0.2 ns

Novel beta-gamma detection system developed for trace contamination analysis

Enhanced measurement precision over previous studies

Abstract

Materials selection for rare event physics requires high performance detectors and customized analyses. In this context a novel $\beta$-$\gamma$ 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 $^{238}\textrm{U}$ contaminations through neutron activation analysis, since the activation product $^{239}\textrm{Np}$ decays to a relatively long-lived isomeric state of $^{239}\textrm{Pu}$, 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 $\beta^-$ decay of $^{239}\textrm{Np}$ and the delayed events following the de-excitation of the $^{239}\textrm{Pu}$ 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 $^{239}\textrm{Pu}$ level resulted $190.2 \pm 0.2$ ns, thus increasing the precision by about a factor of 20 over previous measurements.