Mp. Unterweger et Ll. Lucas, Calibration of the National Institute of Standards and Technology tritiated-water standards, APPL RAD IS, 52(3), 2000, pp. 527-531
Massic activity values obtained for NBS/NIST tritiated water SRMs 4927 and
4927E, using internal gas-proportional counting, are reported. The massic a
ctivity ratios of all of the available NBS/NIST tritiated water SRMs and sa
mples of the Level 1 and Level 3 tritiated water standards produced by the
National Physical Laboratory (NPL) in 1996 were measured using an extensive
series of liquid-scintillation intercomparisons. New massic activity value
s obtained for the NPL standards, using the gas counting results for SRM 49
27E and the results of the liquid-scintillation intercomparison, are also r
eported. A new determination of the half-life of tritium was made using mas
sic activity data for SRM 4927 over a period of 38 years. The new value is
(4504 +/- 9) (one standard deviation) days. This value differs significantl
y from the previous NBS/NIST value but is in good agreement with the value
recommended in the Evaluated Nuclear Structure Data File (ENSDF). Published
by Elsevier Science Ltd.