Safeguards Analytical Laboratory
Pulse-Counting Thermal Ionization Mass Spectrometer for Environmental Analysis
Thermal ionization mass spectrometry is used to measure the U and Pu concentration and isotopic composition in environmental samples. The basic technique is described in the section for destructive analysis of nuclear material samples. However, for measurements of environmental samples, a very high sensitivity is needed, extending into the nanogram (10-9 g) and picogram (10-12 g) range. This is achieved by the use of special sample treatment procedures, electrodeposition of the sample elements on the mass spectrometer filament and by use of a pulse counting detection system with high abundance sensitivity. The mass spectrometer is a Finnigan MAT-262 instrument, as shown below. Isotopic spikes (233U, 242Pu or 244Pu) are added to the samples during chemical processing to ensure that a fixed amount of U or Pu is recovered and to be used in the isotope dilution method to measure the concentration of U or Pu in the sample. Isotope ratios are measured for all isotopes of U or Pu relative to the spike isotope from which the element concentration and isotopic composition is calculated.
Finnigan MAT-262 Mass Spectrometer