A new standard solution of 243Am, an important radionuclide for the US and international environmental-measurements communities, was developed and disseminated at NIST as SRM 4332E.
The radionuclide 243Am decays by alpha emission and it is the most stable of the americium isotopes however, is not found in nature. It is formed in the nuclear fuel cycle by neutron capture on 242Pu followed by beta decay. It is used as a monitor for radioactive contamination and as a tracer on radiochemical processes. The certified massic activity for 243Am in radioactive equilibrium with 239Np was obtained by 4pabliquid scintillation (LS) spectrometry with three commercial LS counters. The LS detection efficiency was calculated using the CN2003 code for the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT)/NIST method with composition matched LS cocktails of a 3H standard as the efficiency detection monitor. The combined standard uncertainty (k = 2) on the standardization is 0.9 %. Based on comparative LS measurements, the certified value of the massic activity for SRM 4332E was in agreement with that for the previously issued SRM 4332D to within 1.0 %, with a k = 2 combined uncertainty on the two massic activities of 1.2 %.