A novel approach for the determination of 238Pu by thermal ionization mass spectrometry (TIMS) using interfering element correction methodology

A novel approach using interfering element correction (IEC) methodology is presented for the determination of 238Pu in Pu by thermal ionization mass spectrometry (TIMS). The IEC methodology is based on the use of 235U as a monitor isotope to correct for the ubiquitous isobaric interference of 238U at 238Pu. The procedure involves the addition of enriched 235U (>90 atom%) externally to the Pu sample. The 238U/235U atom ratio in the sample is determined experimentally by monitoring the intensities of ions with m/z 254 and 251, corresponding to 238UO+ and 235UO+, respectively. Subsequently, 238Pu/239Pu atom ratio is determined by using Pu+ ion at different heating temperatures of vaporization and ionization filaments. The methodology is evaluated using NIST-SRM 947 isotopic reference material with 238Pu abundance close to 0.25 atom% and a synthetically prepared sample containing about 2 atom% of 238Pu. The approach is simple and holds promise for the characterization of new reference materials of 238Pu using TIMS.