Evaluation of mass spectrometry and radiation detection for the analysis of radionuclides

Radioactive elements are of increasing importance in the areas of human health and safety, the environment, use in terrorism, and nuclear nonproliferation. Accurate and sensitive measurement of fission products, medical isotopes, and actinide species are a vital part of the job entrusted to the national laboratories. Several competing techniques exist. They can be mainly summarized into two categories: radiation and mass spectrometric detection methods. Traditional radiometric counting methods, which are based on the measurement of natural decay of radionuclides, play an important role in the detection of radionuclides. Fission track analysis, which uses thermal neutron induced fission to detect fissionable isotopes, now reaches a limit of detection (LOD) of 106 atoms. Of the mass spectrometric detection techniques, inductively coupled plasma mass spectrometry, provides the best sensitivity for the cost in low-level determinations of long-lived radionuclides. Other methods, such as thermal ionization mass spec and accelerator mass spec can provide greater sensitivity in some cases but the cost is higher. Depending on the types of mass analyzers, LOD varies from ng/l to pg/l. More importantly, mass spectrometry is capable of offering precise isotopic ratio information that may act as a fingerprint for identifying the origins of nuclear materials. As the technology matures mass techniques now can provide suitable detection of the shorter-lived isotopes. This criterion is critical as the prompt determination of radionuclides is becoming of overriding importance. Radiometric information displayed in a manner that allows for easy comparison to mass counting is provided. The information can then be used as a general guide to determine the most suitable method to use for the prompt determination of radionuclides. (author)