METHOD DEVELOPMENT FOR SIGNATURES IN NUCLEAR MATERIAL FOR NUCLEAR FORENSIC PURPOSES

Sammanfattning: Nuclear forensics is a scientific discipline where signatures in nuclear and other radioactive material are investigated and evaluated in order to aid in criminal investigations concerning these materials. Examples of signatures that may be useful is the age and isotopic composition of the nuclear material and trace elements in the material. In order for evidence to hold up in court, the information extracted from forensic investigations need to be accurate and precise. This work shows some possibilities and limitations of using two common techniques for measurements of nuclear material and other radioactive material: gamma spectrometry and inductively coupled plasma - mass spectrometry. One part of this work is dedicated to the applicability of hand-held instruments. The categorization of uranium using low-resolution gamma spectrometry and possibility of using signatures in high activity 241Am sealed sources that can be obtained by HPGe were explored. In the other part, methods for high confidence measurements of lanthanides using ICP-MS were developed and problems arising when performing these analyses with as small uncertainties as possible were investigated. The results show that nuclear forensic analyses require deep understanding in the measurement process in order to provide accurate results. Low-resolution instruments in the current configuration have been shown to be a poor choice for categorization of uranium. On the other hand, there are a number of interesting signatures in 241Am-sources that can be provided by high-resolution gamma spectrometry. By using chemical separations or desolvating sample introduction systems in combination with careful data evaluation, it is possible to measure the lanthanide series without spectral interferences and with low uncertainties. By investing meticulous work to the analyses, it is possible to achieve measurements with high confidence.