63Ni half-life: a new experimental determination and critical review

The 63Ni half-life has been determined to be 101.06 ± 1.97 a based on three independent measurements, conducted over the past 27 years, of the massic activity of gravimetrically-related 63Ni sources. The 63Ni assays were performed initially (in 1968) by microcalorimetry using an assumed mean β− energy per decay, and subsequently (in 1984 and 1995) by 4πβ liquid scintillation spectrometry with 3H-standard efficiency tracing. The present result is the first and only determination of the 63Ni half-life which is based on actually following the radioactive decay of 63Ni. All previously reported determinations were derived from specific activity evaluations. These earlier determinations have been scutinizingly reviewed as part of this work. Some of these previous values can be revised in lieu of more recent nuclear data and on consideration of the experimental details. Based on a critical evaluation of the extant data set, a 63Ni half-life value of T=101.1 ± 1.4 a is recommended.