Half-life of 176Lu

Half-life measurements of lutetium-176 using underground HPGe-detectors

The half-life of (176)Lu was determined by measuring the (176)Lu activity in metallic lutetium foils. Three different HPGe-detectors located 225 m underground were employed for the study. Measurements using the sum-peak method were performed and resulted in an average massic activity of (52.61±0.36) Bq g(-1). The foils were of natural isotopic abundance so using the massic activity and the value of the natural isotopic abundance of (2.59±0.01)%, a half-life of (3.722±0.029)×10(10)a could be calculated.

Half-life of 176Lu

The half-life of 176Lu, measured using gamma-ray spectrometry, has been found to be (3.56+/-0.07)x10(10)yr. Comparison has been made between present results and literature data.

Improved limit on the electron capture decay branch of 176Lu

We have performed searches for the electron-capture decay branches of 176Lu to the ground state and first excited state of 176Yb. No evidence of either decay mode was observed. From these measurements we have established upper limits on both of these possible branches that are each > 20 times more stringent than the single previously published limit.

Calibration of the lutetium-hafnium clock

Well-defined constants of radioactive decay are the cornerstone of geochronology and the use of radiogenic isotopes to constrain the time scales and mechanisms of planetary differentiation. Four new determinations of the lutetium-176 decay constant (lambda176Lu) made by calibration against the uranium-lead decay schemes yield a mean value of 1.865 +/- 0.015 x 10(-11) year(-1), in agreement with the two most recent decay-counting experiments. Lutetium-hafnium ages that are based on the previously used lambda176Lu of 1.93 x 10(-11) to 1.94 x 10(-11) year(-1) are thus approximately 4% too young, and the initial hafnium isotope compositions of some of Earth's oldest minerals and rocks become less radiogenic relative to bulk undifferentiated Earth when calculated using the new decay constant. The existence of strongly unradiogenic hafnium in Early Archean and Hadean zircons implies that enriched crustal reservoirs existed on Earth by 4.3 billion years ago and persisted for 200 million years or more. Hence, current models of early terrestrial differentiation need revision.