Use of Compton suppression gamma ray spectrometry to determine 239Pu.

239Pu has been characterized by gamma-ray spectroscopy for a level higher than the usual environmental ones typically needing alpha spectrometry, ICP-MS or TIMS. The higher activities typically have applications in reprocessing, safeguards verification, and nuclear forensics. For activities of hundreds of Bq/g, it is possible to use gamma ray spectrometry for 239Pu characterization. A soil reference standard of 185 Bq/g (75 ng/g) was measured on a 79% efficient HPGe with a digital Compton suppression system. The ratios of the counting statistics for suppressed and unsuppressed uncertainties for various 239Pu photopeaks were determined. The effects of self-attenuation on the low energy gamma rays were evaluated, and it was determined that Compton suppression was an effective characterization method of 239Pu after accounting for self-attenuation.

Discovery of neutron activation analysis.

It is well known that George Hevesy and Hilde Levi were the original discoverers of neutron activation analysis. However, there were many other researchers in Europe that firstly unknowingly and knowingly discovered the neutron, and others who experimented in neutron induced radioactivity. A historical timeline of the several parallel experiments in a very short period is given in this synopsis. It eventually was Hevesy and Hilde to first use the powerful technique of neutron activation analysis for analytical chemistry.

A feasibility study on the determination of 90Sr food-chain transfer using stable strontium as a surrogate and neutron activation analysis.

We evaluated the applicability of neutron activation analysis for investigating the potential mobility of 90Sr in a pasture area in Hungary. To measure strontium concentrations, we made use of the 84Sr(n,γ)85Sr radiative capture reaction using neutron activation analysis and performed gamma spectroscopy using Compton-suppression techniques on the resulting 514.0 keV gamma ray. Our values for soil-to-plant transfer factors value of 1.6 (2.2) kg kg-1 were in agreement with recommended values from the ICRP and IAEA, as well as similar studies performed by independent researchers. Our values for plant-to-animal transfer coefficients and concentration ratios varied from suggested values by several orders of magnitude to agreement with other values. Based on our results the utilized transfer of stable strontium could not be regarded as a convenient substitute to help clarify the long-term transfer of radioactive strontium in the environment, because short term dosing was applied. Neutron activation analysis provides a unique niche as a technique with very little chemical processing and short sample analysis times.

Neutron activation analysis for the characterization of seawater uranium adsorbents.

This work details the development of an iterative neutron activation analysis (NAA) based workflow to precisely quantify metal ion uptake in an adsorbent. The workflow is iterative because it explores the dependence between independent variables defining the adsorbent fabrication procedure and the time-dependent uptake. It can be adapted to other adsorbents provided they have an affinity for ions which are amenable to efficient quantification using NAA. For this work, the ability of silver nanoparticles to mitigate the negative effects of biofouling on uranium transfer to an adsorbent was ultimately of interest, and hence motivates the development of this method. The limits of U detection and quantification were found to be 0.609 and 3.01µgg-1, respectively; these were obtained using modest irradiation and counting times. The uncertainties arising from the NAA procedure were no more than 9.9%, far smaller than other sources of uncertainty present in the analysis. These results provided solid evidence that adsorbent shape and structure, rather than uniformity of composition, drives variability in adsorption of uranium.

Determination of cesium transfer factors by instrumental neutron activation analysis.

Food-chain models are used to predict radionuclide ingestion after fallout deposition. These models include those transfer processes (soil-to-plant transfer factor(s) [TF], plant-to-animal transfer coefficient(s) [TC] and concentration ratio [CR]) that are likely to be important for radiological assessment. The range of variability for transfer factors for the same plant groups is great, about 4-5 orders of magnitude, which limits their applicability. A better way to determine the best estimate the factors for radiocaesium and other important radionuclides is if the site-specific data are available. Soil, plant and animal samples were collected from a pasture area in Hungary during the vegetation period in 2016. Stable 133Cs concentration was analysed by comparative method with neutron activation analysis (NAA). The comparator and the samples were irradiated in thermal neutron flux 2.55 × 1012 ncm-2s-1 for 2 h (soil) and 6 h (vegetation, animal samples) in the TRIGA Mark II research reactor at the Nuclear Engineering Teaching Laboratory. After an appropriate decay time (12 days) the samples were measured by gamma-spectrometry and analysed. The observed stable caesium TCpm (0.48-0.53) and CRpm (0.41-0.45) were very close to 137Cs factors in the IAEA 2009 Report of 0.49 and 0.54, respectively. This methodology is particularly suitable for the simultaneous study of natural caesium in ecosystem compartments. Consequently, the transfer of stable caesium in a pasture field may be regarded as a useful analogy in predicting the long-term changes of 137Cs affected by site-specific environmental factors.

The application of illite supported nanoscale zero valent iron for the treatment of uranium contaminated groundwater.

In this study, nanoscale zero valent iron I-NZVI was investigated as a remediation strategy for uranium contaminated groundwater from the former Cimarron Fuel Fabrication Site in Oklahoma, USA. The 1 L batch-treatment system was applied in the study. The result shows that 99.9% of uranium in groundwater was removed by I-NZVI within 2 h. Uranium concentration in the groundwater stayed around 27 µg/L, and there was no sign of uranium release into groundwater after seven days of reaction time. Meanwhile the release of iron was significantly decreased compared to NZVI which can reduce the treatment impact on the water environment. To study the influence of background pH of the treatment system on removal efficiency of uranium, the groundwater was adjusted from pH 2-10 before the addition of I-NZVI. The pH of the groundwater was from 2.1 to 10.7 after treatment. The removal efficiency of uranium achieved a maximum in neutral pH of groundwater. The desorption of uranium on the residual solid phase after treatment was investigated in order to discuss the stability of uranium on residual solids. After 2 h of leaching, 0.07% of the total uranium on residual solid phase was leached out in a HNO3 leaching solution with a pH of 4.03. The concentration of uranium in the acid leachate was under 3.2 µg/L which is below the EPA's maximum contaminant level of 30 µg/L. Otherwise, the concentration of uranium was negligible in distilled water leaching solution (pH = 6.44) and NaOH leaching solution (pH = 8.52). A desorption study shows that an acceptable amount of uranium on the residuals can be released into water system under strong acid conditions in short terms. For long term disposal management of the residual solids, the leachate needs to be monitored and treated before discharge into a hazardous landfill or the water system. For the first time, I-NZVI was applied for the treatment of uranium contaminated groundwater. These results provide proof that I-NZVI has improved performance compared to NZVI and is a promising technology for the restoration of complex uranium contaminated water resources.

Disequilibrium in the uranium and actinium series in oil scale samples.

We have investigated the disequilibrium of the uranium and actinium series and have found both 226Ra (90,200 ± 4300 Bq/kg) and 228Ra have activity concentrations orders of magnitude higher that 238U (1.83 ± 0.36 Bq/kg) and 232Th (7.0 ± 0.4) which are at the head of the decay series. As well the activity concentration of 210Pb (24,400 ± 1200 Bg/kg) was about 3.6 times less than 226Ra. Once an efficiency curve was constructed summing corrections for specific isotopes in the decay change also needed to be taken in consideration. Furthermore, self-attenuation of the photons especially the 46.5 keV belonging to 210Pb was calculated to be 78% since the scale had elevated elemental concentrations of high-Z elements such as barium and strontium.

Characterization of bauxite residue (red mud) for 235U, 238U, 232Th and 40K using neutron activation analysis and the radiation dose levels as modeled by MCNP.

This study employs thermal and epithermal neutron activation analysis (NAA) to quantitatively and specifically determine absorption dose rates to various body parts from uranium, thorium and potassium. Specifically, a case study of bauxite residue (red mud) from an industrial facility was used to demonstrate the feasibility of the NAA approach for radiological safety assessment, using small sample sizes to ascertain the activities of 235U, 238U, 232Th and 40K. This proof-of-concept was shown to produce reliable results and a similar approach could be used for quantitative assessment of other samples with possible radiological significance. 238U and 232Th were determined by epithermal and thermal neutron activation analysis, respectively. 235U was determined based on the known isotopic ratio of 238U/235U. 40K was also determined using epithermal neutron activation analysis to measure total potassium content and then subtracting its isotopic contribution. Furthermore, the work demonstrates the application of Monte Carlo Neutral-Particle (MCNP) simulations to estimate the radiation dose from large quantities of red mud, to assure the safety of humans and the surrounding environment. Phantoms were employed to observe the dose distribution throughout the human body demonstrating radiation effects on each individual organ.

Gamma-gamma coincidence performance of LaBr3:Ce scintillation detectors vs HPGe detectors in high count-rate scenarios.

A radiation detection system consisting of two cerium doped lanthanum bromide (LaBr3:Ce) scintillation detectors in a gamma-gamma coincidence configuration has been used to demonstrate the advantages that coincident detection provides relative to a single detector, and the advantages that LaBr3:Ce detectors provide relative to high purity germanium (HPGe) detectors. Signal to noise ratios of select photopeak pairs for these detectors have been compared to high-purity germanium (HPGe) detectors in both single and coincident detector configurations in order to quantify the performance of each detector configuration. The efficiency and energy resolution of LaBr3:Ce detectors have been determined and compared to HPGe detectors. Coincident gamma-ray pairs from the radionuclides 152Eu and 133Ba have been identified in a sample that is dominated by 137Cs. Gamma-gamma coincidence successfully reduced the Compton continuum from the large 137Cs peak, revealed several coincident gamma energies characteristic of these nuclides, and improved the signal-to-noise ratio relative to single detector measurements. LaBr3:Ce detectors performed at count rates multiple times higher than can be achieved with HPGe detectors. The standard background spectrum consisting of peaks associated with transitions within the LaBr3:Ce crystal has also been significantly reduced. It is shown that LaBr3:Ce detectors have the unique capability to perform gamma-gamma coincidence measurements in very high count rate scenarios, which can potentially benefit nuclear safeguards in situ measurements of spent nuclear fuel.

Characterization and identification of na-cl sources in ground water.

Elevated concentrations of sodium (Na+) and chloride (Cl-) in surface and ground water are common in the United States and other countries, and can serve as indicators of, or may constitute, a water quality problem. We have characterized the most prevalent natural and anthropogenic sources of Na+ and Cl- in ground water, primarily in Illinois, and explored techniques that could be used to identify their source. We considered seven potential sources that included agricultural chemicals, septic effluent, animal waste, municipal landfill leachate, sea water, basin brines, and road deicers. The halides Cl-, bromide (Br), and iodide (I) were useful indicators of the sources of Na+-Cl- contamination. Iodide enrichment (relative to Cl-) was greatest in precipitation, followed by uncontaminated soil water and ground water, and landfill leachate. The mass ratios of the halides among themselves, with total nitrogen (N), and with Na+ provided diagnostic methods for graphically distinguishing among sources of Na+ and Cl- in contaminated water. Cl/Br ratios relative to Cl- revealed a clear, although overlapping, separation of sample groups. Samples of landfill leachate and ground water known to be contaminated by leachate were enriched in I and Br; this provided an excellent fingerprint for identifying leachate contamination. In addition, total N, when plotted against Cl/Br ratios, successfully separated water contaminated by road salt from water contaminated by other sources.

Review of soluble uranium removal by nanoscale zero valent iron.

Uranium (U) has been released to surface soil and groundwater through military and industrial activities. Soluble forms of U transferred to drinking water sources and food supplements can potentially threaten humans and the biosphere due to its chemical toxicity and radioactivity. The immobilization of aqueous U onto iron-based minerals is one of the most vital geochemical processes controlling the transport of U. As a consequence, much research has been focused on the use of iron-based materials for the treatment of U contaminated waters. One material currently being tested is nanoscale zero-valent iron (nZVI). However, understanding the removal mechanism of U onto nZVI is crucial to develop new technologies for contaminated water resources. This review article aims to provide information on the removal mechanism of U onto nZVI under different conditions (pH, U concentration, solution ion strength, humic acid, presence of O2 and CO2, microorganism effect) pertinent to environmental and engineered systems, and to provide risk or performance assessment results with the stability of nZVI products after removal of U in environmental restoration.

Non-destructive determination of uranium, thorium and 40K in tobacco and their implication on radiation dose levels to the human body.

The naturally occurring radionuclides of (235)U, (238)U and (232)Th and their daughter products are a potential major source of anthropogenic radiation to tobacco smokers. Often overlooked is the presence of (40)K in tobacco and its implication to radiation dose accumulation in the human body. In this study, these three radiation sources have been determined in four typical US cigarettes using neutron activation analysis (NAA). The NAA reactions of (238)U(n,γ)(239)U, (232)Th(n,γ)(233)Th and (41)K(n,γ)(42)K were used to determine (235)U, (238)U and (232)Th and (40)K, respectively. The activity of (238)U can easily be determined by epithermal NAA of the (238)U(n,γ)(239)U reaction, and the activity of (235, 234)U can easily be deduced. Using isotopic ratios, the activity due to (40)K was found by the determined concentrations of (41)K (also by epithermal neutrons) in the bulk material. Each gram of total potassium yields 30 Bq of (40)K. The annual effective dose for smokers using 20 cigarettes per day was calculate to be 14.6, 137 and 9 µSv y(-1) for (238,235,) (234)U, (232)Th and (40)K, respectively. These values are significantly lower that the dose received from (210)Po except for (232)Th.

Self-attenuation as a function of gamma ray energy in naturally occurring radioactive material in the oil and gas industry.

Self-attenuation correction factors were experimentally determined using radioactive point sources in combination with a subject material of naturally occurring radioactive material (NORM) obtained from oil exploration waste products. The self-attenuation correction factors were taken across a range of gamma ray energies from 41.73 to 1408.0keV. It is noted that the greatest amount of self-attenuation occurs in the energy regime below 200keV and rises to near zero attenuation at higher energies for these types of samples. For the 46.5keV gamma ray of (210)Pb there can be an underestimation of 62%.

Measuring the noble metal and iodine composition of extracted noble metal phase from spent nuclear fuel using instrumental neutron activation analysis.

Masses of noble metal and iodine nuclides in the metallic noble metal phase extracted from spent fuel are measured using instrumental neutron activation analysis. Nuclide presence is predicted using fission yield analysis, and radionuclides are identified and the masses quantified using neutron activation analysis. The nuclide compositions of noble metal phase derived from two dissolution methods, UO2 fuel dissolved in nitric acid and UO2 fuel dissolved in ammonium-carbonate and hydrogen-peroxide solution, are compared.

Naturally occurring heavy radioactive elements in the geothermal microcosm of the Los Azufres (Mexico) volcanic complex.

The Los Azufres geothermal complex of central Mexico is characterized by fumaroles and boiling hot-springs. The fumaroles form habitats for extremophilic mosses and ferns. Physico-chemical measurements of two relatively pristine fumarolic microcosms point to their resemblance with the paleo-environment of earth during the Ordovician and Devonian periods. These geothermal habitats were analysed for the distribution of elemental mass fractions in the rhizospheric soil (RS), the native volcanic substrate (VS) and the sediments (S), using the new high-sensitivity technique of polarized x-ray energy dispersive fluorescence spectrometry (PEDXRF) as well as instrumental neutron activation analysis (INAA) for selected elements. This work presents the results for the naturally occurring heavy radioactive elements (NOHRE) Bi, Th and U but principally the latter two. For the RS, the density was found to be the least and the total organic matter content the most. Bi was found to be negligibly present in all substrate types. The average Th and U mass fractions in the RS were higher than in the VS and about equal to their average mass fractions in the S. The VS mass fraction of Th was higher, and of U lower, than the mass fractions in the earth's crust. In fact for the fumaroles of one site, the average RS mass fractions of these elements were higher than the averaged values for S (without considering the statistical dispersion). The immobilization of the NOHRE in the RS is brought about by the bio-geochemical processes specific to these extremophiles. Its effectiveness is such that despite the small masses of these plants, it compares with, or may sometimes exceed, the immobilization of the NOHRE in the S by the abiotic and aggressive chemical action of the hot-springs. These results indicate that the fumarolic plants are able to transform the volcanic substrate to soil and to affect the NOHRE mass fractions even though these elements are not plant nutrients. Mirrored back to the paleo times when such plant types were ubiquitous, it would mean that the first plants contributed significantly to pedogenesis and the biogeochemical recycling of even the heaviest and radioactive elements. Such plants may potentially be useful for the phytostabilisation of soil moderately contaminated by the NOHRE. Furthermore where applicable, geochronology may require taking into account the influence of the early plants on the NOHRE distributions.

Multielement preconcentration of trace metals from natural waters by solvent extraction with an alkylated oxine derivative.

Kelex 100, a commercially available alkylated oxine derivative, is shown to be effective, in purified form, for the simultaneous extraction of trace levels of Cd(II), Co(II), Cu(II), Mn(II), Ni(II), Pb(II), and Zn(II) from natural waters into toluene. The high lipophilicity of the extractant and its chelates affords large preconcentration factors in a single batch-extraction. Back-extraction with a small volume of nitric acid provides additional enrichment for subsequent determination of total (soluble) metal by graphite-furnace atomic-absorption spectrometry (GFAAS). Calibration with standard solutions can be used, which has advantages over the method of standard additions.

The impact of heavy metals from environmental tobacco smoke on indoor air quality as determined by Compton suppression neutron activation analysis.

The method of instrumental neutron activation analysis (NAA) has been improved for air filter samples in the determination of low level heavy metals in indoor air. By using the techniques of epithermal neutron irradiation in conjunction with Compton suppression, the detection limits of cadmium, arsenic and antimony measurements have been dramatically reduced to 2 ng for Cd, 0.2 ng for As, and 0.03 ng for Sb. The determination of these heavy metals in particulate material generated from cigarette smoking in indoor environments has been conducted. Other elements, Br, Cl, Na, K, Zn were also found at elevated levels.

Elemental source signatures of aerosols from the Canadian high Arctic.

The seasonal fluctuations of antimony, arsenic, indium, manganese and vanadium have been measured in airborne particulate matter from 1982-1987 at Alert in the Canadian high Arctic. Calculations of enrichment factors have shown that arsenic and antimony are very enriched in the wintertime aerosol. While wintertime ratios of non-crustal manganese/non-crustal vanadium were in agreement with previously published work, summertime ratios often resulted in negative values. A re-evaluation of the crustal Mn/V ratio was undertaken by looking at this ratio during the summertime and assuming that nearly all the airborne particulate matter was derived from crustal matter. Principal Source Contribution Function Analyses were performed for arsenic, indium and manganese. The results suggested that these important regional signatures can now be characterized as coming from distinct European and Asian areas. This improvement in area resolution is much more satisfactory than citing the usual attribution of an overall Eurasian source.

An evaluation of atmospheric deposition of trace elements into the Great Lakes.

High-volume air samplers were used to collect aerosol samples on Whatman 41 air filters at the Canadian air sampling stations Burnt Island, Egbert, and Point Petre. Once collected, the samples were analyzed for trace elements by neutron activation analysis. Air concentrations of over 30 trace elements were determined. A special focus was made to utilize Compton suppression gamma-ray spectroscopy and epithermal irradiations to enhance the detection limits of neutron activation analysis. These techniques allowed for the determination of trace elements at very low levels. Results of the study of the trace-metal dry deposition into Lakes Huron and Ontario indicated that the majority of the total deposition resulted from crustal materials. However, dry deposition is also a significant pathway for many toxic anthropogenic trace metals into the Great Lakes.

An evaluation of thermal and epithermal neutron activation analysis compton suppression methods for biological reference materials.

For neutron activation analysis (NAA), the usual matrix problems of sodium, chlorine, and bromine are well known to give rise to high backgrounds that inhibit the determination of several trace elements for short-lived or medium-lived NAA. For long counting times in long-lived NAA, very low backgrounds are required to achieve good sensitivities. We have investigated the use of thermal and epithermal NAA in conjunction with Compton suppression to determine several elements such as arsenic, antimony, cadmium, and mercury, at the level of a few nanograms. The values of these techniques are discussed in contrast to the standard radiochemical methods.