Resonance ionization mass spectroscopy for trace determination of plutonium in environmental samples

 Resonance ionization mass spectroscopy (RIMS) is a sensitive and isotope selective method and well suited for trace analysis of plutonium in the environment. After the chemical isolation of plutonium from soil, air filters or urine, e.g., it is electrolytically deposited as hydroxide on a tantalum backing and covered with a thin titanium layer. By heating such a sandwich filament in the RIMS-apparatus under vacuum an atomic beam of plutonium is produced. The atoms are ionized by a three-step resonant excitation using pulsed dye lasers, and the ions are mass-selectively detected with a time-of-flight (TOF) spectrometer and a multi channel plate detector. RIMS yields a low detection limit of 106–107 atoms and a high element and isotope selectivity. This technique has been used for the investigation of soil samples from the Chernobyl area, sediments from the Mururoa Atoll and urine samples with respect to the total amount of plutonium and its isotopic composition.