M. P. Unterweger

M. P. Unterweger coauthored a 2000 study of measurement calibration for water standards containing tritium. The paper combined measurements using a proportional counter with liquid scintillation counting comparisons. It also followed massic activity data spanning 38 years to estimate a tritium half-life of $4504\pm 9$ days, with the uncertainty specified as one standard deviation.^[ref]

The long time record makes a useful distinction visible. A reference sample's radioactive activity changes through radioactive decay even when its chemical identity is unchanged. In an ideal closed sample with constant half-life $T_{1/2}$,Measurements made at different times must therefore be related to a common time before differences can be interpreted as inconsistent standards. A half-life determination and a detector comparison address related but distinct parts of that problem.