Speaker
Description
In 2020, the National Institute of Standards and Technology (NIST) reported on a primary activity standardization of 224Ra in equilibrium with its progeny. Subsequently, measurements of the absolute emission intensity for its main gamma ray were reported in the contexts of a bilateral comparison with the National Physical Laboratory (NPL). More recently, NIST has standardized 212Pb in equilibrium with its progeny and included an improved approach to the propagation of decay data uncertainties. Here, the high-purity germanium (HPGe) gamma-ray spectrometry data collected during those standardizations are used to assess the absolute photon emission intensities for the main gamma rays of 224Ra, 212Pb, and their progeny. In addition, the half-life for 212Pb, was measured using several HPGe detectors, ionization chambers, and a well-type NaI(Tl) detector.
The measured decay data were compared with the evaluated values for 212Pb reported by K. Auranen and E.A. McCutchan Nuclear Data Sheets 168, 117 (2020) as part of the Evaluated Nuclear Data Structure File (ENSDF, available at https://www.nndc.bnl.gov/) and by A.L. Nichols as part of the Decay Data Evaluation Project (DDEP) evaluated in 2001 and reevaluated in 2004 and 2010 (available in the Laboratoire National Henri Becquerel (LNHB) website http://www.lnhb.fr/nuclear-data/nuclear-data-table/).
Agreement between the absolute gamma-ray emission intensities determined by NIST and NPL was found. Most measured photon emission intensities are within 2 % of the evaluated values, except for gamma rays with low emission intensities, for which the observed differences were larger. There is an improvement in the precision quoted for many of the observed gamma rays. The measured half-life values were compared with the values used in the DDEP evaluation and the recommended value in the ENSDF evaluation. The measured values agree with the tabulated ones within the measurement uncertainties.
