Update of NIST half-life results corrected for ionization chamber source-holder instability

Abstract

As reported at the ICRM 2011, it was discovered that the source holder used for calibrations in the NIST 4πγ ionization chamber (IC) was not stable. This has affected a large number of half-life measurement results previously reported and used in compilations of nuclear data. Corrections have been made on all of the half-life data based on the assumption that the changes to the ionization chamber response were gradual. The corrections are energy dependent and therefore radionuclide specific. This presentation will review our results and present the recommended changes in half-life values and/or uncertainties.

Decay Data Evaluation Project (DDEP): Updated evaluation of the 133Ba, 140Ba, 140La and 141Ce decay characteristics

“…All experimental data published up to 2016 along with new compilations, analyses and corrections were taken into account in the current evaluations. In particular, as a consequence of a major a e-mail: chechev@khlopin.ru problem discovered in the NIST ionization chamber used in their radionuclide calibration studies over many years, the NIST corrections to these half-life data in 2014 were taken into account [10].…”

“…No new 140 [10]. Uncertainties in the evaluated and recommended half-lives were assigned on the basis of the smallest experimental uncertainty in the original data sets [9].…”

“…We updated the 2004 DDEP half-life evaluation of 133 Ba on the basis of enforced adjustment to earlier NIST and PTB measurements in previous years [10,15] (see comments for 133 Ba on the DDEP web site [7]). A final set of ten selected experimental values were analysed by LWEIGHT to determine a weighted average half-life of 3849.3 d with an external uncertainty of 2.3 d (reduced-χ 2 /(χ 2 ) crit is 10.0/2.4).…”

Nuclear Decay Data for the International Reactor Dosimetry Library for Fission and Fusion (IRDFF): Updated Evaluations of the Half-Lives and Gamma Ray Intensities

“…The DDEP 22 Na half-life evaluation by M. Galán [12] was updated in this work using the 2014 corrected NIST half-life value of 2.6013 (19) years [6] (instead of 2.6037 (3) years previously reported). No new measurements have been published during the intervening period of 2009-2014.…”

“…2.1, 2.2 in [3]). In relation to the problem discovered in the NIST calibration method [5], the 2014 corrected NIST half-life values [6] were introduced into the available experimental data sets, where required, and the re-evaluated half-life values have been obtained for long-lived radionuclides.…”