Precise determination of 244Cm by 244Cm/239Pu alpha ratio measurements

Abstract

This work describes a method developed for the precise determination of Cm in a solution. The method is based on accurate spiking of a ²⁴⁴Cm solution having a known isotopic vector but unknown concentration, with a Pu reference standard. The specific ²⁴⁴Cm activity and concentration is determined through an alpha spectrometric measurement of the ²⁴⁴Cm/Pu alpha peak ratio. The alpha ratio is determined after removing interferences from ²⁴¹Am and ²³⁸Pu in the ²⁴⁴Cm peak and by modelling ²⁴⁴Cm tailing into the ²³⁹Pu region of interest. The precision of the method was experimentally determined comparing 20 samples prepared from the same spiked solution by direct alpha planchette deposition with or without addition of a surfactant. The 20 samples were measured in 5 different alpha detectors belonging to two different alpha spectrometry systems. A total of 90 measurements yielded a combined measurement and evaluation precision of the Cm/Pu alpha ratio of 0.27% (k = 2). This result was compared to measurements of the Cm/Pu alpha ratio in 7 samples prepared by electrodeposition. The comparison indicated that sample preparation by electrodeposition gives a slightly increased uncertainty. Finally, the overall uncertainties involved in the analysis method are discussed and an uncertainty budget is estimated. The method is robust and by minimising uncertainties in the individual steps, the concentration of Cm can be determined with an overall uncertainty less than 0.670% with a coverage factor of 2 standard deviations.