The accuracy of radioisotopic ages is, at present, limited by the accuracy
of radioactive decay constants. A literature survey reveals that decay cons
tants used in geo- and cosmochronology usually are assigned uncertainties o
f ca. 1% but that then are very much larger unaccounted discrepancies betwe
en decay constants reported by different "counting groups" as well as diffe
rences between results derived from counting experiments and from the compa
rison of ages obtained on the same samples by utilizing different radioacti
ve clocks. An extension and partial revision of the decay constants recomme
nded in 1976 for adoption in geo- and cosmochronology by the International
Union of Geological Sciences (IUGS) appears both desirable and feasible, gi
ven the analytical improvements of the last 20 years. We call for a concert
ed effort to achieve improvements in the near future. For this it will be n
ecessary to rigorously evaluate counting biases in counting determinations,
initial daughter contamination for ingrowth experiments, and the existence
of truly "point-like" geological events for age comparison approaches. Cop
yright (C) 2001 Elsevier Science Ltd.