Matrix effects in plutonium isotope ratio measurements using thermal ionization mass spectrometry

Through high fidelity measurements of four different plutonium certified reference material standards from New Brunswick Laboratory, the mass fractionation correction factor for the Pu-240/Pu-239 major isotope ratio measurements by the total evaporation methodology using thermal ionization mass spectrometer instruments is shown to depend on the elapsed time since separation of the decay products from the analyzed plutonium fraction. Systematic biases arising from this matrix dependence of the mass fractionation correction factor are larger than the precision obtained in routine TE measurements of the Pu-240/Pu-239 major isotope ratio using thermal ionization mass spectrometry regarded as the gold standard for these measurements. LA-UR-21-21,941.