Uncertainties in Measuring Lifetimes of Nuclear Excited States using a Fast Electronic Timing System made of NaI (Tl) Scintillators

Abstract

Measurements of the lifetimes of nuclear excited states need to be as accurate as possible due to their crucial role in making or verifying various theoretical predictions in the nuclear science and astrophysics. Nevertheless, metrological difficulties in these measurements have brought about controversies that significantly influence the quest to understand the atomic structure, decay processes and nuclear reactions. Among the obstacles are the accuracy and precision of the systems and techniques used for measuring the lifetime of an excited state. It follows that any hypothesis regarding the nuclear behavior can only be considerable upon verification and accountability of stability and uncertainty of the devices used during the experiments for measuring the lifetime of a nuclear excited state. As a step towards accurate measurements of lifetimes of excited states, this work focuses on evaluating the uncertainties of such measurements. In doing so, a fast timing system made of two NaI(Tl) detectors have been developed to measure the lifetime of the 5/2+ excited state of ¹³³Cs using the gamma-gamma coincidences. An uncertainty budget showed the sources of uncertainties in measuring the nuclear excited state’s lifetime include timewalk, drift effect, selection of the region of interest, background effects and counting statistics. The total uncertainty in measuring the 5/2+ excited state of ¹³³Cs was found to be 0.024 ns, representing 0.382% of the nominal lifetime value. This implies that the system can accurately measure the lifetimes of excited nuclear states ranging from 1 ns.