Standard Reference Materials: Standardization of 243Am (SRM 4332f)

Summary

A new Standard Reference Material (SRM) of Am-243 has been produced and calibrated. Americium's most stable isotope, americium-243, has a half-life of (7367 ± 23) years. It decays into neptunium-239 through alpha decay. Americium can be produced in kilogram quantities and has a few practical uses. It is used in smoke detectors and can be used as a portable source of gamma rays.

Description

The certified massic activity for ²⁴³Am was obtained by 4παβ LS spectrometry with two commercial LS counters. The beta detection efficiencies for the ²⁴³Am daughter (²³⁹Np) were calculated using the CN2003 code for the CIEMAT/NIST efficiency tracing (CNET) method with composition-matched LS cocktails of a ³H standard as the efficiency detection monitor.  Confirmatory measurements were performed by LS counting comparative measurements against SRM 4332e, which was standardized in 2008 by CIEMAT/NIST Efficiency Tracing using ³H as the detection efficiency monitor, live-timed anticoincidence (LTAC) measurements; alpha spectrometry of electrodeposited sources; and by gamma spectrometry with high-resolution HPGe detectors. Confirmatory values by LS comparative measurements, LTAC, alpha spectrometry, and gamma-ray spectrometry agreed with the CNET certified value by -0.21 %, -0.21 %, -0.21 %, and -0.46 %, respectively. Triple-to-double coincidence (TDCR) was used to determine the counting rate ratio for R_4332f/ R_4332e. The ratio obtained by TDCR agreed with the ratio by LS to within -0.05%. The certified massic activity of ²⁴³Am (with the ²⁴¹Am impurity correction) in SRM 4332f, is (48.18± 0.63) Bq·g^-1 at k = 2 as of 1200 EST, 8 March 2024.

The ratio of alpha-emitting impurities ²⁴¹Am/²⁴³Am = 0.00162 ± 0.00007 was obtained by alpha spectrometry.  Based on gamma ray spectrometry ²⁴¹Am/²⁴³Am = 0.0019 ± 0.0007. Mass spectrometry for (²⁴¹Am+ ²⁴¹Pu)/²⁴³Am agrees with alpha spectrometry ²⁴¹Am/²⁴³Am ratio to +3.3 %.