The Fourth Collaborative Material Exercise (CMX-4) of the Nuclear Forensics International Technical Working Group (ITWG) registered the largest participation for this exercise in nuclear forensics, with seven of the 17 laboratories participating for the first time. Each of the laboratories had their strategic role to play in its respective country, analyzing real-world samples using their in-house resources. The scenario was fictitious but was thoughtfully crafted to engage participants in nuclear forensic investigations. In this paper, participants from five of the first-time laboratories shared their individual experience in this exercise, from preparation to analysis of samples.

A laboratory exercise for calculation of true coincidence summing correction factors as well as calculating the effect of deviations between sample and standard source (filling height) was developed. This laboratory exercise was held in a masters course in nuclear chemistry the first time during fall 2013. The aim of the exercise was to high-light the importance of correcting for biases due to different systematic effects in gamma spectrometric measurements.

Four calculation codes were implemented on experimental data to calculate corrections of common systematic effects within high resolution gamma spectrometry. The detector parameters were sparsely optimized to imitate the usage that can be expected from personnel with limited experience. The transfer of the efficiency from the calibration geometry (60 ml, density 1.0 g/cm 3 ) to 200 ml geometry (density 1.5 g/cm 3 ) failed with all codes, which was discouraging. However, a majority of the other corrected activities deviated with less than 10 % from the reference activity values, even for density corrections or when corrections had been calculated for new source-detector-geometries. Smaller deviations, around 5 % or less, were achieved when corrections were done within the calibrated geometry. This shows a robustness of the calculation codes even if the in-data is not perfectly optimized.

In CAMNAR, an extensive interlaboratory exercise on the analytical methods used to determine several radionuclides present in the environmental samples was organized. Activity concentration of different natural radionuclides, such as Rn-222, Pb-210, Po-210, K-40, Ra-226, Ra-228 and isotopes of uranium, in addition to artificial Cs-137 and Am-241 were analysed from lake sediment samples and drinking water. The measurement techniques were gamma-ray spectrometry, alpha spectrometry, liquid scintillation counting and inductively coupled plasma mass spectrometry. Twenty six laboratories from nine Nordic and European countries participated in the intercomparison. Extraordinary variation between the results reported by different laboratories were revealed for some radionuclides indicating the need of future intercomparisons especially in the case of natural water samples.