Revision of the ANSI N42.14 performance standard for Ge gamma-ray spectrometry (2023)

Environmental Pollution, Volume 205, 2015, pp. 394-402

This work intended to explain the challenges of the fingerprints based source apportionment method for polycyclic aromatic hydrocarbons (PAH) in the aquatic environment, and to illustrate a practical and robust solution. The PAH data detected in the sediment cores from the Illinois River provide the basis of this study. Principal component analysis (PCA) separates PAH compounds into two groups reflecting their possible airborne transport patterns; but it is not able to suggest specific sources. Not all positive matrix factorization (PMF) determined sources are distinguishable due to the variability of source fingerprints. However, they constitute useful suggestions for inputs for a Bayesian chemical mass balance (CMB) analysis. The Bayesian CMB analysis takes into account the measurement errors as well as the variations of source fingerprints, and provides a credible source apportionment. Major PAH sources for Illinois River sediments are traffic (35%), coke oven (24%), coal combustion (18%), and wood combustion (14%).

Journal of Environmental Radioactivity, Volumes 178–179, 2017, pp. 212-231

Environmental transfer models assume that organically-bound tritium (OBT) is formed directly from tissue-free water tritium (TFWT) in environmental compartments. Nevertheless, studies in the literature have shown that measured OBT/HTO ratios in environmental samples are variable and generally higher than expected. The importance of soil-to-leaf HTO transfer pathway in controlling the leaf tritium dynamics is not well understood. A model inter-comparison of two tritium transfer models (CTEM-CLASS-TT and SOLVEG-II) was carried out with measured environmental samples from an experimental garden plot set up next to a tritium-processing facility. The garden plot received one of three different irrigation treatments – no external irrigation, irrigation with low tritium water and irrigation with high tritium water. The contrast between the results obtained with the different irrigation treatments provided insights into the impact of soil-to-leaf HTO transfer on the leaf tritium dynamics. Concentrations of TFWT and OBT in the garden plots that were not irrigated or irrigated with low tritium water were variable, responding to the arrival of the HTO-plume from the tritium-processing facility. In contrast, for the plants irrigated with high tritium water, the TFWT concentration remained elevated during the entire experimental period due to a continuous source of high HTO in the soil. Calculated concentrations of OBT in the leaves showed an initial increase followed by quasi-equilibration with the TFWT concentration. In this quasi-equilibrium state, concentrations of OBT remained elevated and unchanged despite the arrivals of the plume. These results from the model inter-comparison demonstrate that soil-to-leaf HTO transfer significantly affects tritium dynamics in leaves and thereby OBT/HTO ratio in the leaf regardless of the atmospheric HTO concentration, only if there is elevated HTO concentrations in the soil. The results of this work indicate that assessment models should be refined to consider the importance of soil-to-leaf HTO transfer to ensure that dose estimates are accurate and conservative.

Corrosion Science, Volume 112, 2016, pp. 347-363

Understanding the corrosion susceptibility of Magnox alloys during short- and long-term storage in moist air is important. Corrosion of Magnox AL80, Magnox ZR55 and magnesium has been studied in air containing water partial pressures between 200vppm and ∼80000vppm, at temperatures of 46°C–96°C. Specimens were exposed to air, with and without CO₂, and argon gas. Metal consumption rates were measured and corrosion products characterised, using optical and scanning electron microscopy, energy dispersive x-ray microanalysis, x-ray diffraction and secondary ion mass spectrometry. Results show the importance of CO₂ gas for suppressing breakaway corrosion in moist air.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Volume 954, 2020, Article 161866

High-order angular correlations of fast neutrons emitted by spontaneous fission in californium-252 (²⁵²Cf) have been measured with a 2D array of 15 EJ-309 organic liquid scintillation detectors. These are compared with the results of Geant4 simulations using both an uncorrelated, average fission model and correlated fission models, which have also been used to quantify the impact of detector cross-talk on these distributions. In general, a bipolar trend is observed up to and including quadruple events, that is, ${\theta }_{12}$, ${\theta }_{13}$ and ${\theta }_{14}$. A bias as $\theta \to 0^{\circ }$ in these data is observed that is consistent with the expectation of cross-talk being more prevalent for nearest-neighbour detectors. This is observed to be reduced for higher orders (${\theta }_{13}$ and ${\theta }_{14}$ relative to ${\theta }_{12}$) and for wider gate widths (25ns rather than 10ns), consistent with this phenomenon being cross-talk. For the case of ${\theta }_{13}$, each of the composite angular distributions for the 14 detector positions $24^{\circ }\le \theta \le 336^{\circ }$ have also been derived: a variation from a bipolar trend to a more isotropic behaviour, accompanied by a reduction in the relative level of response, is observed in these data for detector angles orthogonal to the reference detector at $0^{\circ }$ consistent with the majority of neutrons being emitted from accelerated fragments. This research constitutes an important step towards quantifying and managing cross-talk as arrays of organic scintillators attract interest for practical applications such as nuclear materials assay.

Measurement, Volume 145, 2019, pp. 648-650

Measurement of nuclear materials by ISOCS technique an important and significant tool for IAEA activities verification. ISOCS technique able to measuring samples with different geometry. In this work, ISOCS technique was used to calculate the absolute efficiency of the Hyper Pure Germanium (HPGe) detector. The calculated absolute efficiency of the detector was used in combination with experimental work to determine U-235 mass in cylindrical NM samples. A good agreement was obtained when compared estimated and declared values of ²³⁵U mass content with difference in the ranged from −0.827% to 1.635%.

Environmental Pollution, Volume 242, Part A, 2018, pp. 519-527

This study provides contamination levels, distributions and source apportionment of PAHs in surface sediments in the mid-Adriatic and along the Croatian coast. Median summed concentrations of parent and alkyl-PAHs are circa 10 times lower in the off-shore transect stations of the mid-Adriatic (22.3 and 18.2 μg.kg⁻¹ d.w.) than the ranges determined at the coastal stations, including those of Kaštela bay (227–331 and 11.7–197 μg.kg⁻¹ d.w., respectively). The highest levels, circa 20 times higher, were found in Šibenik bay (median 6603 and 3051 μg.kg⁻¹). The overall range of PAH concentrations spans more than 2000 times between the lowest and the highest contamination level. The geographical distributions reflect the presence of strong gradients at local and regional scales. A major factor influencing sedimentary PAH distributions at local scale appears to be the distance from their known continental and coastal upstream emission sites (urban, industrial, harbour …), whereas at regional scale, this distribution depends more on the routes of entry of PAHs into the study area. Two combustion and one petroleum model source profiles of PAHs were determined by alternative least square analysis. Benzo[b+j]fluoranthenes and fluoranthene/pyrene are compounds characterizing two pyrogenic sources respectively, while signatures of alkyl-substituted homologues (phenanthrenes/anthracenes, fluranthenes/pyrenes, chrysenes and dibenzothiophenes) delineate a petrogenic source profile. The quantitative apportionment of source contributions shows significant geographical differences, with a dominant petrogenic source found along the mid-Adriatic transect (approximately 74%) and in Kaštela bay (61%). In the coastal sediments about a fifty-fifty contamination mix is assigned to a petrogenic/pyrogenic source of PAHs (47% and 53% respectively), whereas in Šibenik bay a strong predominance is apportioned to the combustion compounds (81%).