Mass spectrometry is a well-established, highly versatile technique that offers high sensitivity, high selectivity and high precision in combination with the potential for high accuracy. Credible nuclear forensic conclusions, however, need to be based on validated procedures and on measurement techniques that are well understood. Nuclear forensic investigations typically start with non-destructive determination (i.e. high-resolution gamma spectrometry) of the radionuclides present in the sample and a visual inspection, followed by optical microscopy of the material. Subsequently, samples are taken for electron microscopy and for chemical analysis. Mass spectrometry is certainly the most prominent and versatile analytical methodology that can be applied.
A number of variants of mass spectrometry can be used in nuclear forensics, each able to provide valuable information to nuclear scientists analysing nuclear material that enables the drawing of conclusions in support of non-proliferation and law enforcement investigations (see table 3.1). Thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICP-MS) and secondary ion mass spectrometry (SIMS) allow determination of key parameters such as isotopic composition of major and minor constituents and the concentration of chemical impurities in the nuclear material. More sophisticated techniques, such as accelerator mass spectrometry (AMS) and resonance ionization mass spectrometry (RIMS), are currently being investigated for their applicability to nuclear forensics challenges.
This chapter provides some details on different mass spectrometric techniques, outlines their general principles and limitations, and illustrates their application in nuclear forensic investigations. Sections I-III describe the most prominent mass spectrometric techniques: TIMS, ICP-MS and SIMS, respectively. Section IV describes two techniques, AMS and RIMS, that are applied only in special cases.