Software based solutions to ensure quality and correctness within gamma ray spectrum analysis

This dissertation is a collection of various software based solutions that are used to assure the reliability and quality of gamma-ray spectrum analysis. Most of these ideas were tested during the development of the gamma-ray spectrum analysis software Sampo in 1989-2009. Main issues are related to ensure the correctness of calibrations, gamma-ray peak finding, gamma-ray peak area determination, radionuclide identification and management of data acquisition and data management. Reliable gamma spectrum analysis is a necessary pre-requisite for various applications in the field of nuclear verification. This work presents how the analysis and calibration tools have been used in environmental sample analysis, neutron activation analysis, verification of spent nuclear fuel, mobile in-situ measurements and in nuclear test verification. If the gamma-ray spectrum is complicated, two major contributors are necessary to assure correctness of the analysis: visual management of the spectrum analysis, particularly in the peak area determination, and tools to assess the statistical significance of small peaks. Quantification of the isotopes is not always necessary for analysis purposes. Sometimes it is enough to be able to assure the presence or absence of certain radionuclide. In those cases, a simple hypothesis testing during the measurements will suffice to optimize the use of detector time. Gamma-ray spectrum calibration correctness can be checked with relatively simple test measurements before the actual measurements are taken. This is especially important when there is a need to report immediately after a critical measurement, for example in case of real-time in-situ measurements that are needed to evaluate possible fallout after a nuclear accident. In some applications, the number of spectra to be analyzed is so high that automatic data evaluation is needed. In this case, it is important that the applied software is able to warn the user about spectra which require human review or which can provide an alarm of interesting findings. Precisely, this kind of system was set up to assure the preparedness of environmental sample (air filter) analysis. This system has successfully been used for more than 10 years in the surveillance of Comprehensive Nuclear Test-Ban-Treaty measurements at various National Data Centres that wish to monitor environment. (author)