The uncertainty of the half-life

Abstract

Half-life measurements of radionuclides are undeservedly perceived as 'easy' and the experimental uncertainties are commonly underestimated. Data evaluators, scanning the literature, are faced with bad documentation, lack of traceability, incomplete uncertainty budgets and discrepant results. Poor control of uncertainties has its implications for the end-user community, varying from limitations to the accuracy and reliability of nuclearbased analytical techniques to the fundamental question whether half-lives are invariable or not. This paper addresses some issues from the viewpoints of the user community and of the decay data provider. It addresses the propagation of the uncertainty of the halflife in activity measurements and discusses different types of half-life measurements, typical parameters influencing their uncertainty, a tool to propagate the uncertainties and suggestions for a more complete reporting style. Problems and solutions are illustrated with striking examples from literature.

Evidence against solar influence on nuclear decay constants

“…An overview of standardisation techniques and their sources of error can be found in the special issues 44(4) and 52(3) of Metrologia [41,42] and references in [25,28]. …”

“…At the heart of this controversy are the metrological difficulties inherent to the measurement of half-lives [28–30]. From a metrological point of view, it is obvious that instruments, electronics, geometry and background may vary due to external influences such as temperature, pressure, humidity and natural or man-made sources of radioactivity.…”

Believable statements of uncertainty and believable science

“…Recent measurements at PTB have caused most of the earlier anomalies to disappear as more sources of experimental bias have been revealed and eliminated [34, 35]. Half-life measurement is subject to many sources of bias, not all of which are readily detected [36]. Although there is decreasing evidence for non-constant radioactive decay rates, the search continues in some laboratories.…”

Half-life measurement of the medical radioisotope 177Lu produced from the 176Yb(n,γ) reaction

“…The uncertainty of each component was calculated using the uncertainty propagation formula proposed by Pommé [25] and combined in quadrature to determine the standard uncertainty of the half-life. The uncertainty budget is presented in Table 2.…”