Standardization of ²⁴¹Am (SRM 4322c)

A new standardization for ²⁴¹Am was completed.  Americium-241 decays 100 % by alpha transitions to Np-237 with 432.6 years.  It is commonly found in ionization type smoke detectors and is a potential fuel for long-lifetime radioisotope thermoelectric generators (RTGs). The certified massic activity for ²⁴¹Am was obtained by 4πα liquid scintillation (LS) counting using two different LS measurement systems. The combined standard uncertainty (k = 2) on the standardization is 0.32 %. This solution is gravimetrically linked to a ²⁴¹Am stock solution used to prepare several previous NIST ²⁴¹Am standards, including a primary live-timed anticoincidence standardization in 2007, two proficiency testing standards issued for a nuclear power plant measurement assurance program and for the Integrated Consortium of Laboratory Networks, as well as to SRM 4322c. A remeasurement of SRM 4322c at the time of this work in 2019 agreed with the 2007 certified value to within 0.05 %