Sample processing improvements for actinide analysis in low level samples
Mr David Child1, Mr Robert Chisari1, Dr Michael Hotchkis1, Ms Archana Amatya Joshi1
1ANSTO, Lucas Heights, Australia
A review of the performance statistics of actinides samples measured on the VEGA AMS facility at the Centre for Accelerator Science, ANSTO indicated that inadequate yield was being achieved on a particular subset of samples, namely plutonium isotopic measurements on chemistry blanks, and on low level “clean” low matrix samples (e.g. swipes and filters) when using our routine method . Absolute yields of AMS targets are difficult to ascertain due to the use of isotopic dilution analysis since measurements yield only relative ratios, and variations in ion source output and ionisation efficiency between targets make it hard to compare absolute count rates. The measured count rates of plutonium isotopes in these samples however were routinely <50% of comparable calibration and tuning materials however leading us to conclude that there was a yield issue. Additionally, development was desired on a simplified processing method for multi-actinide extraction and isolation including U, Np, Pu and Am isotopes.
An investigation was conducted into the chemical loss of Pu in blanks and low matrix samples during processing as well as to determine the efficacy of a proposed multi-actinide extraction method. This investigation was able to successfully reproduce the systematic loss of Pu during ion-exchange extraction chromatography which was correlated to a lack of iron in the sample matrix and its utility as a redox agent for fixing Pu during separation. A revised sample processing method was then developed and tested, confirming an increase in Pu yield >90% for all sample types including blanks and low matrix materials using this revised method. This method employed a streamlined, single pass through utilising paired Eichrom UTEVA/TEVA pre-packed resin cartridges. Additionally >80% yield was achieved on a series of tests samples for U, Np, and Am tracers when employing this revised ion exchange separation method.
This revised method will be presented along with data demonstrating the improved performance of this method.
1. Johansen, M.P., et al., Differentiating Fukushima and Nagasaki plutonium from global fallout using ²⁴⁰Pu/²³⁹Pu atom ratios: Pu vs. Cs uptake and dose to biota. 2021. 754: p. 141890.
David Child has worked within the accelerator group at ANSTO for over 20 years as a chemist and sample preparation expert, supporting projects across nuclear safeguards and forensics, actinides bomb pulse dating for geosciences, cosmogenic dating and radiocarbon dating.