63Ni, its half-life and standardization:: Revisited

Recent liquid scintillation (LS) measurements at the National Institute of Standards and Technology (NIST) and at the Laboratoire National Henri Becquerel (LNHB) on a standardized Ni-63 solution that has been tracked for nearly 40 years have resulted in several important findings: (i) a Ni-63 half-life value of 101.2 +/- 1.5 a has been determined with the present decay data. This value is consistent with a previous specific activity determination and with an earlier value from decay measurements; and it appears to be more satisfactory than a recent data evaluator's recommended value of 98.7 a. (ii) All solution standards of Ni-63 as disseminated by NIST for the past 38(+) years are internally consistent with past and recent standardizations. (iii) Primary LS standardizations of Ni-63 by the triple-to-double coincidence ratio (TDCR) method and by CIEMAT/NIST H-3-standard efficiency tracing (CNET) appear to be comparable, although the latter methodology is believed to be inherently inferior. (iv) There is excellent measurement agreement between NIST and LNHB for Ni-63 primary standardizations. (C) 2007 Elsevier Ltd. All rights reserved.