In decision making, e.g. conformity to a specification like a reference value or a requirement, the decision rule applied shall be documented. Furthermore, if the measurement uncertainty is considered in the decision process the associated probability, or risk, that a measurement result is above (or below) a reference value shall be taken into account. In this work it is shown that for gross alpha and gross beta measurements the evaluation method, GUMUF (GUM Uncertainty Framework) or MC (Monte Carlo), may also be important and influence the decisions taken when measurement results are very close to the reference value. Therefore the evaluation method and assumptions of the input quantities may also be important to document. Moreover, decision makers or users of measurement results should be aware of possible differences and/or consequences due to the evaluation method regardless of the decision rule and the choice of evaluation method.

Gamma spectrometric measurements to determine the isotopic composition and total uranium mass in UO2 pellets (D = 7.5 mm; H = 3.5 mm, rho = 10 g/cm3) were carried out. The required efficiency curve was obtained by applying the efficiency transfer method from a calibration standard (D = 65 mm; H = 20 mm) of a slightly acidified water solution. The average isotopic composition of ten UO2 pellets was consistent with values of natural uranium given by IUPAC. The average relative bias for the 235U/238U amount ratio was-0.73% using the 1001 keV gamma line for 238U and 0.50% using the 63 keV gamma line (186 keV was always used for 235U). For the total uranium mass, the mean deviation as compared to mass determinations using a balance was 5.5% using the 1001 keV gamma line for 238U and 4.3% using the 63 keV gamma line.

A method for the measurement of gross alpha and gross beta activities for low alpha-to-beta activity ratios is presented. Measurement of the gross alpha activity would still be important from an internal dose perspective when the gross beta activity is dominating, since a significant dose contribution may come from alpha emitting radionuclides. The method is intended for screening of drinking water after a radiological emergency when many samples would be valuable to be measured during a short period of time.

In this study, calculation of decision threshold and detection limit expressed in counts for low-level radioactivity measurements were evaluated and compared to a Monte Carlo method for the case of paired Poisson-distributed observations, i.e. for discrete variables. The calculated characteristic limits obtained from Monte Carlo calculations were compared with analytical expressions given in literature. The results in this study show that the equations given by Currie are in good agreement with the results from the Monte Carlo calculations simulating nuclear counting applications with a low number of observed counts. An exception is observed for a background corresponding to zero counts. This study also shows that at a low number of counts, the specific boundary conditions of the interval that represents counts corresponding to the presence of the analyte (>or ≥), have an impact on the false positives and negatives rates as defined by the parameters α and β.

The efficiency transfer procedure from a geometry where a volume source was placed directly on the endcap of a germanium detector to three different distant geometries was carried out using the EFFTRAN code. One of these distant geometries included absorbers consisting of poly(methyl methacrylate). The efficiency transfer to this geometry therefore had to be realized as a two-stage transfer, since a direct efficiency transfer is not possible using EFFTRAN in such a case. Efficiency transfer to all three distant geometries yielded results which can be considered as fit-for-purpose in e.g. most of the applications of gamma ray spectrometry.

Radioanalytical methods for the determination of isotopes of Pu, Am and Cm in water samples from nuclear power plants were compared and further developed in a Nordic project (Optimethod) through two intercomparison exercises among Nordic laboratories. With this intercomparison, the analytical performance of some laboratories was improved by modification of the analytical method and adopting new techniques. The obtained results from the two intercomparisons for alpha emitting transuranium isotopes are presented, and the lessons learnt from these intercomparison exercises are discussed.

A National Nuclear Forensic Library (NNFL) is a useful nuclear forensics tool which consists of information and subject matter expertise on radioactive and nuclear (RN) materials produced, used or stored within a State. If RN material is found out of regulatory control the NNFL can be used as part of a nuclear forensics investigation to help identify whether or not the material is consistent with a country’s national holdings. In previous work, a number of signatures which can be useful to identify sealed sources of 241 Am were investigated. To validate the measurement results, an official query concerning information about two of the previously investigated 241 Am sources was sent to the United States Department of State, the international point-of-contact (POC) for the U.S. NNFL. The aim of this work is to show how data obtained in a characterization of a radioactive source can be used in conjunction with an NNFL to investigate the history of a source out of regulatory control.

A method for the measurement of the isotopic composition and time since last chemical separation (age) of plutonium is presented. The method includes alpha spectrometric measurement of 238Pu, 239Pu and 240Pu where the ratio of 239Pu and 240Pu was determined using spectral deconvolution, and liquid scintillation counting of 241Pu, after chemical separation of plutonium and americium. For the age determination, the 241Pu determined using liquid scintillation counting was combined with alpha spectrometric measurement of 241Am. The results of the isotopic composition were compared with certified reference materials with known isotopic composition, and the results of the age determination were compared with literature values of the separation dates.

The minimum detectable activity (MDA) for gamma spectrometric measurements was studied as a function of filling height for two detectors having different background characteristics and for two sample matrices: a water sample with a low content of natural radionuclides, and zircon sand, with high activities of uranium and thorium. The zircon sand is also a material in which the self-attenuation of low-energy gamma photons will be high. The results show that for the water sample it is always favourable to completely fill the sample container. However, due to the inherent content of naturally occurring radionuclides in the zircon sand the MDA may not necessarily improve with the filling height, since an increased amount of sample will increase the background in the spectrum as well.

Measurements of the lanthanide series with ICP-SF-MS provide low detection limits but suffer from oxides of the lighter lanthanides interfering on the heavier ones. In this work, two different methods to measure the lanthanide series without interferences, were investigated and compared to measuring the lanthanides directly with a standard sample introduction system. It is shown that by using a desolvating sample introduction system during measurements, the impact of polyatomic interferences are eliminated. It is also shown that using chemical separations to separate the elements in the lanthanide series into three fractions almost eliminates polyatomic interferences, while direct measurements with a standard sample introduction system may lead to inaccurate results due to interferences.

In this work, problems arising from performing trace element analysis using inductively coupled plasma-mass spectrometry with low measurement uncertainties are addressed. It is shown that some reference materials certified for massic concentration of lanthanides may have either deviating concentrations or underestimated measurement uncertainties. It is also shown that the choice of methods for sample preparation and linear regression to perform external calibration is affecting the outcome of the measurement results and their uncertainties. The results show that, from the selection of methods investigated in this work, the lowest measurement uncertainties can be achieved by using weighted linear regression to evaluate the calibration function and gravimetric dilutions of samples.

Calculation of the decision threshold and detection limit of a measurement, or measurement method, are crucial in order to decide if an analyte is present or not and with what confidence it can be quantified. That decision is important in view of possible actions if something would be detected. In this work, a method for calculating these limits using a Monte Carlo method is presented. In the Monte Carlo method any a priori distribution (e.g. normal distribution, rectangular distribution, triangular distribution) of an input quantity can be selected. Differences between the Monte Carlo calculated characteristic limits and the ones calculated according to ISO 11929:2010 is presented. Moreover, suggestions how to calculate the detection limit when it can not be calculated according to the ISO 11929:2010 are given.

True coincidence summing correction factors for 133 Ba, 152 Eu and 125 Sb were determined experimentally for a small volume source and compared with correction factors obtained with three softwares (EFFTRAN-X, GESPECOR and VGSL). The radionuclides investigated have a relatively challenging decay scheme and their spectra are known to suffer from losses due to summation (γ–γ, γ–X and X–X) when measured at close distances on a HPGe detector sensitive to low energy photons. This study shows that the softwares were in good agreement with each other and the experimental data and the calculated activity was consistent with the activity in the volume source.

The self-heating of wood fuel pellets is a well-recognised problem causing fire incidents in the storage of the pellets as well as severe intoxication of workers by elevated carbon monoxide and carbon dioxide levels and oxygen depletion. Possible factors contributing to the self-heating are considered to be autoxidation and microbiological activity, while the role and contribution to the temperature rise caused by the heat of condensation from water vapour condensing during fast changes in the relative air humidity is less investigated. Using Dynamic Vapour Sorption, the water uptake was measured at 25 °C when increasing the RH from 40 to 80% using 35 fuel pellet samples covering a broad variation in pellet raw materials and process equipment found in Europe (both pilot and industrial scale). The equilibrium total water uptake and speed of the uptake were determined. Total water uptake was 4.56% (range 3.69–6.86%) with no systematic difference found related to the scale of production (industry as compared to pilot plant). In addition, the variations within larger groups of raw material (pine, spruce and pine/spruce mixtures) were relatively small, and the mean water uptake did not differ significantly between these groups. An estimation of the overall potential heat release (when raising the RH% from 40 to 80%) made from the experimental results, taking the early fast water uptake process into consideration (2 h counting for half the total uptake), showed that a heat release of 47 kJ/kg of pellets (range 12–63 kJ/kg) and a potential temperature increase of 45 °C is possible. This estimation clearly demonstrates that the heat of condensation released during water condensation in a pellets silo or in a pellets pile should be expected to be a major contributing factor to initiating temperature rise incidents. In addition, such a temperature increase is expected to assist the initiation of, and to increase the speed of autoxidation of fatty acids and other compounds in the material that will further contribute to a temperature rise. Thus, the results in this study have the potential to improve the basis for modelling the self-heating process in pellet silos/storage and to predict the status of a certain pellet batch by presenting a broad basis for expected variation in the important parameters (specific heat capacity C P and thermal conductivity λ eff ) influencing the process, and thus aid in taking preventive actions like venting or shifting the pellets to another silo/pile to reduce risk for self-heating and possible fire.

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.

During the last days of September to the first days of October in 2017, a unique detection of 106Ru was observed in air filters sampled at different locations in Sweden via the national air monitoring network. Furthermore, measurements of precipitation also showed the presence of 106Ru. This initiated soil sampling and in situ gamma-ray spectrometry at one of the locations.

In case of a radiological emergency situation involving e.g. fission of uranium or plutonium, analysis of radioactive strontium will be of importance. The primary radionuclides of interest are 90Sr, its progeny 90Y and 89Sr. A few days following an event, 89Sr will be the predominant radioisotope of strontium. Most methods found in the literature are valid and applicable when measuring 90Sr, but when samples contain both 89Sr/90Sr interference problematics arise. How these interferences are dealt with will have an effect on the uncertainty of the 90Sr determination. This work aims at evaluating three measurement approaches, all mentioned in the literature, with respect to the measurement uncertainty when determining 90Sr in an emergency preparedness situation and to propose a suitable measurement strategy.

Low enriched uranium samples of unknown origin were analyzed by 16 laboratories in the context of a Collaborative Materials Exercise (CMX), organized by the Nuclear Forensics International Technical Working Group (ITWG). The purpose was to compare and prioritize nuclear forensic methods and techniques, and to evaluate attribution capabilities among participants. This paper gives a snapshot of the gamma spectrometric capabilities of the participating laboratories and summarizes the results achieved by gamma spectrometry.

An international group of laboratories participating in CMX-4 subjected three samples to comparative nuclear forensic analysis using uranium assay and trace element analysis techniques to determine if the samples had similar or different origins. Uranium assay indicated that two pellet samples (ES-2 and ES-3) were nearly pure UO 2 while the black powder sample ES-1 was primarily UO 2 with UO 3 and/or U 3 O 8 forms present as impurities. Trace element analysis by five of the six participating laboratories reported molybdenum concentrations below 10 µg/g U in all of the exercise samples, suggesting the same likely facility of origin for all three samples.

Calculation and reporting of combined measurement uncertainties are important in decision making processes, and a more proper uncertainty estimation can reduce the risk and/or the cost associated with decisions for example after radiological incidents and in free release measurements of radioactive waste. However, sound decisions demand a sound uncertainty estimation. In this work we present the possible consequences when uncertainty propagation is applied to gamma-ray spectrometry measurements involving assumed probability density functions for an efficiency transfer having different metrological quality by comparison with Monte Carlo simulations.