Uranium Isotopes Research Articles

Determination of Uranium Isotopic Ratio by ICP-OES Using Optimal Sensitivity Position Analysis.

Isotopic composition analysis of natural and depleted uranium by inductively coupled plasma optical emission spectrometry (ICP-OES) requires the use of a high-resolution instrument due to the very slight isotopic shifts between the atomic emission spectra of the 238U and 235U isotopes. In this work, we show that conventional ICP-OES (without high-resolution optics) can be used for highly accurate uranium isotopic analysis, on par with the results obtained by ICP-MS. Such accurate measurements are achieved by applying a preparatory mathematical procedure termed the optimal sensitivity position (OSP) procedure. In the OSP procedure, a theoretical spectrum for 238U is constructed and subtracted from the measured spectra of calibration solutions encompassing various isotopic ratios. The resultant spectra are used to locate the optimal measurement positions for both major uranium isotopes (238U and 235U) and the background measurement position. Herein, the optimal measurement positions are revealed to be located not at each isotope's peak maximum but at 424.427, 424.409, and 424.390 nm for 238U, 235U, and the background position, respectively. These locations remained stationary during the period of this work, implying that the use of a routine mathematical procedure is not required before every analysis. The OSP procedure offers a direct and highly accurate approach for determining the isotopic ratio of uranium in a relatively cheap and simple fashion. Furthermore, this work also demonstrates the possibility of greatly enhancing ICP-OES capabilities using mathematical analysis of spectra.

Measurement of uranium isotope ratios in Fukushima-accident contaminated soil samples using multi collector inductively coupled plasma mass spectrometry

In the present study, 137Cs and 238U activity concentrations, 234U/238U activity ratio, and 235U/238U isotope ratio were measured in fifteen soil samples collected from the exclusion zone around the Fukushima Daiichi Nuclear Power Station (FDNPS). The 137Cs activity concentrations of Fukushima-accident contaminated soil samples ranged from 29.9 to 4780 kBq kg−1 with a mean of 2007 kBq kg−1. On the other hand, the 238U activity concentrations of these soil samples ranged from 5.2 to 22.4 Bq kg−1 with a mean of 13.2 Bq kg−1. The activity ratios of 234U/238U ranged from 0.973 to 1.023. The 235U/238U isotope ratios of these exclusion zone soil samples varied from 0.007246 to 0.007260, and they were similar to the natural terrestrial ratio confirming the natural origin. Using isotope dilution technique, the 235U/137Cs activity ratio was theoretically estimated for highly 137Cs contaminated soil samples from Fukushima exclusion zone ranged from 5.01 × 10−8 - 6.16 × 10−7 with a mean value of 2.51 × 10−7.

Expanded uncertainty modeling of the uranium isotope dilution standards

In this paper, a statistical uranium isotope dilution mass spectrometry approach is presented to simulate the wide range of spike-sample mixed ratios of 235U/238U, in terms of their related expanded uncertainties and uncertainty budget indexes. To obtain the lowest expanded uncertainty in uranium isotope dilution mass spectrometry (U-IDMS) technique, uranium certified materials of U-CRM 112A (spike) and U-CRM 149 (treated as unknown) are statistically employed and simulated. The simulated data is further applied to project U-IDMS samples by using the “Guide to the Expression of Uncertainty in Measurement (GUM)” software.

Measurement of Radon (222Rn) Concentrations in the Basaltic Rocks of Yarmouk River, Jordan

This article was conducted to measure radon concentration levels in the Yarmouk River Basalt (YRB), North-Jordan. The YRB is of Quaternary in age and occurred as a successive sheet with a total thickness of 122 meters. The Yarmouk River Basalt is classified into four major phases. Namely, Yarmouk Sheet basalt, Yarmouk blocky basalt, Yarmouk massive basalt, and Yarmouk exfoliated. Furthermore, each major phase is subdivided into several flows. Sixteen samples are measured by using Nuclear Track Detector (Columbia Resin CR-39) in the laboratory. The results show that the concentration of radon is gradually decreased from the lower basalt first phase towards the upper fourth phase in considerable amounts. The values range from 12413.12 to 4137.71 Bq/m3, with an average value of 6635.74 Bq/m3. The results of this investigation indicate that the uranium isotopes element decay is the origin of radon emitted from the interstitial glass in the basalt rocks, rather than 222Rn emission along with fractures or major faults.

Combining Uranium, Boron, and Strontium Isotope Ratios (234U/238U, δ11B, 87Sr/86Sr) to Trace and Quantify Salinity Contributions to Rio Grande River in Southwestern United States

In semi-arid to arid regions, both anthropogenic sources (urban and agriculture) and deeper Critical Zone (groundwater with long flow paths and water residence times) may play an important role in controlling chemical exports to rivers. Here, we combined two anthropogenic isotope tracers: uranium isotope ratios (234U/238U) and boron isotope ratios (δ11B), with the 87Sr/86Sr ratios to identify and quantify multiple solute (salinity) sources in the Rio Grande river in southern New Mexico and western Texas. The Rio Grande river is a major source of freshwater for irrigation and municipal uses in southwestern United States. There has been a large disagreement about the dominant salinity sources to the Rio Grande and particularly significant sources are of anthropogenic (agriculture practices and shallow groundwater flows, groundwater pumping, and urban developments) and/or geological (natural groundwater upwelling) origins. Between 2014 and 2016, we collected monthly river samples at 15 locations along a 200-km stretch of the Rio Grande river from Elephant Butte Reservoir, New Mexico to El Paso, Texas, as well as water samples from agricultural canals and drains, urban effluents and drains, and groundwater wells. Our study shows that due to the presence of localized and multiple salinity inputs, total dissolved solids (TDS) and isotope ratios of U, B, and Sr in the Rio Grande river show high spatial and temporal variability. Several agricultural, urban, and geological sources of salinity in the Rio Grande watershed have characteristic and distinguishable U, Sr, and B isotope signatures. However, due to the common issue of overlapping signatures as identified by previous tracer studies (such as δ18O, δD, δ34S), no single isotope tracer of U, Sr, or B isotopes was powerful enough to distinguish multiple salinity sources. Here, combining the multiple U, Sr, and B isotope and elemental signatures, we applied a multi-tracer mass balance approach to quantify the relative contributions of water mass from the identified various salinity end members along the 200-km stretch of the Rio Grande during different river flow seasons. Our results show that during irrigation (high river flow) seasons, the Rio Grande had uniform chemical and isotopic compositions, similar to the Elephant Butte reservoir where water is stored and well-mixed, reflecting the dominant contribution from shallow Critical Zone in headwater regions in temperate southern Colorado and northern New Mexico. In non-irrigation (low flow) seasons when the river water is stored at Elephant Butte reservoir, the Rio Grande river at many downstream locations showed heterogeneous chemical and isotopic compositions, reflecting variable inputs from upwelling of groundwater (deeper CZ), displacement of shallow groundwater, agricultural return flows, and urban effluents. Our study highlights the needs of using multi-tracer approach to investigate multiple solutes and salinity sources in rivers with complex geology and human impacts.

Investigation and correlation of radioactive hazards with magnetic parameters and heavy metals of dwelling sand from two major rivers in south India – A comparative study

Cauvery and Palar, two major rivers in Tamilnadu, India, have importance for irrigation, drinking, electricity and river sand is used as a major material of building construction in India. The natural radionuclides such as uranium, thorium and potassium (238U, 232Th, 40K) isotopes are investigated through gamma ray spectrometer with NaI(Tl) detector. The average values of radionuclides and in-situ dose are measured. Related parameters like absorbed dose (ADin & ADout), Annual Effective Doe Equivalent (Ein & Eout), and also hazard indices to assess radiation exposure to human such as average radium equivalent (Raeq), external (Hex)and internal (Hin) hazard indices, Radioactive heat production (RHP), internal and external Excess Lifetime Cancer Risk (ELCRin and ELCRout), Alpha (Iα), Gamma Index (Ig) and Annual Gonadal dose (AGDE) are computed and correlated. This study exhibits that almost all the radioactive parameters are in control by comparing to the world average. Nevertheless, the Cauvery River except site no.20 does not produce a radiological hazard. But, the palar river does slightly produce a radiological risk especially site no.6 shows three times of the world average.

Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes

The Paleocene Eocene Thermal Maximum (PETM) represents a major carbon cycle and climate perturbation that was associated with ocean de-oxygenation, in a qualitatively similar manner to the more extensive Mesozoic Oceanic Anoxic Events. Although indicators of ocean de-oxygenation are common for the PETM, and linked to biotic turnover, the global extent and temporal progression of de-oxygenation is poorly constrained. Here we present carbonate associated uranium isotope data for the PETM. A lack of resolvable perturbation to the U-cycle during the event suggests a limited expansion of seafloor anoxia on a global scale. We use this result, in conjunction with a biogeochemical model, to set an upper limit on the extent of global seafloor de-oxygenation. The model suggests that the new U isotope data, whilst also being consistent with plausible carbon emission scenarios and observations of carbon cycle recovery, permit a maximum ~10-fold expansion of anoxia, covering <2% of seafloor area.

Recent fluid flow in ancient meteorites

Meteorites Carbonaceous chondritic meteorites are thought to be fragments broken off parent bodies that orbit in the outer Solar System, largely unaltered since their formation. These meteorites contain evidence of reactions with liquid water that was thought to have been lost or completely frozen billions of years ago. Turner et al. examined uranium and thorium isotopes in several carbonaceous chondrites, finding nonequilibrium distributions that imply that uranium ions were transported by fluid flow. Because this signature disappears after several half-lives of the radioactive isotopes, the meteorites must have been exposed to liquid within the past million years. The authors suggest that ice may have melted during the impacts that ejected the meteorites from their parent bodies. Science , this issue p. [164][1] [1]: /lookup/doi/10.1126/science.abc8116

Carbonaceous chondrite meteorites experienced fluid flow within the past million years.

Carbonaceous chondritic meteorites are primordial Solar System materials and a source of water delivery to Earth. Fluid flow on the parent bodies of these meteorites is known to have occurred very early in Solar System history (first <4 million years). We analyze short-lived uranium isotopes in carbonaceous chondrites, finding excesses of 234-uranium over 238-uranium and 238-uranium over 230-thorium. These indicate that the fluid-mobile uranium ion U6+ moved within the past few 100,000 years. In some meteorites, this time scale is less than the cosmic-ray exposure age, which measures when they were ejected from their parent body into space. Fluid flow occurred after melting of ice, potentially by impact heating, solar heating, or atmospheric ablation. We favor the impact heating hypothesis, which implies that the parent bodies still contain ice.

Форми знаходження радіонуклідів у донних відкладеннях приміщення 012/7 об’єкта «Укриття»

After installation of the Arch of New Safe Confinement (NSC) into design position, precipitations intake in the underroof space of the Shelter object ceased, and water evaporation began from the unorganized accumulations of radioactively contaminated water. As a result of physical and chemical processes of coagulation and deposition of sparingly soluble salts, bottom sediments, containing uranium and radionuclides, formed. The aim of the work is to determine speciation forms of uranium and radionuclides in the bottom sediments, which formed due to the drying out of unorganized accumulations of radioactively contaminated water in room 012/7 of the NSC – Shelter object. Results of the experimental determination of speciation forms of uranium and radionuclides 90Sr, 137Cs, 154Eu, 238Pu, 239+240Pu, 241Am and 244Cm in the bottom sediments of room 012/7 of the NSC – Shelter object are presented. An amount of water-soluble, exchangeable and acid-soluble uranium forms, fission products and transuranium elements in the bottom sediments of room 012/7 of the NSC – Shelter object was determined by the method of consecutive extractions. Content of uranium, 90Sr, 238Pu, 239+240Pu, 241Am and 244Cm in the leaching solutions and insoluble residue was determined by the ion-exchange method. 90Sr activity was determined by beta-radiometric measurements. Activity of 234,235,236,238U, 238Pu, 239+240Pu, 241Am and 244Cm was determined by alpha-spectrometric measurements of uranium, plutonium and americium sources. The concentration of uranium in the bottom sediments of room 012/7 was 1.02 ± 0.26 mg/g. Abundance content of uranium isotopes is 234U – 0.0159, 235U – 1.09, 236U – 0.192 and 238U – 98.71%. Isotope content of uranium in the bottom sediments, on the whole, corresponds to the isotope content of uranium in the irradiated fuel of the Chornobyl NPP 4th unit with an average burnup. The specific activity of 90Sr and 137Cs in the bottom sediments of room 012/7 is in the range of 6∙108−1∙109 Bq/kg. 239+240Pu and 241Am specific activity in the bottom sediments is in the range of 6∙105 – 8∙106 Bq/kg. 90Sr, 137Cs, 154Eu, 238Pu, 239+240Pu, 241Am and 244Сm radionuclides in the bottom sediments are in different physical and chemical forms, which determine their potential mobility. Mainly uranium and 137Cs in the bottom sediments of room 012/7 are in the exchangeable forms. An amount of water-soluble forms of uranium and 137Cs is about 1.5 – 3%. The main amount of 90Sr, more than 60% is in the carbonate forms, which are very soluble in weak acid medium, when pH is 4.8. More than 65% of 238Pu and 239+240Pu in the bottom sediments of room 012/7 are in the acid-soluble forms. Potential mobility of 241Am in the bottom sediments is notably higher than of plutonium in the soluble state, when pH 4.8, transfer more than 40% of 241Am. Relations of activities of radionuclides 137Cs/90Sr, 90Sr/239+240Pu, 241Am/239+240Pu and 44Cm/239+240Pu in the bottom sediments of room 012/7 differ significantly from the similar relations in the fuel containing materials of the Shelter object.

Measurement of uranium isotope ratio by laser ablation absorption spectroscopy

&lt;sec&gt;High precision measurement of uranium isotope ratio (&lt;sup&gt;235&lt;/sup&gt;U/&lt;sup&gt;238&lt;/sup&gt;U) has important application in the field of nuclear energy safety. In this paper, based on high sensitivity tunable absorption spectroscopy technology, combined with the sample processing method of pulsed laser ablation plasma, high-precision measurement of uranium &lt;sup&gt;235&lt;/sup&gt;U/&lt;sup&gt;238&lt;/sup&gt;U isotope ratio in solid material is realized. In the experimental measurement, transitions near 394.4884 nm/394.4930 nm (vacuum) are selected as the &lt;sup&gt;235&lt;/sup&gt;U/&lt;sup&gt;238&lt;/sup&gt;U analytical lines. The influence of buffer gas and its pressure on the persistence time of uranium atom in laser ablated plasma are studied in detail. &lt;/sec&gt;&lt;sec&gt; The experimental results show that different buffer gases have different ability to restrict the movement of particles in the plasma, which leads to different longitudinal expansion velocity of the plasma (perpendicular to the surface of the sample), and increases the persistence time of uranium atoms in the laser beam. The effect of pressure change on plasma evolution can be reduced by adding buffer gas. When helium is used as the buffer gas, the persistence time of uranium atoms in the plasma is longer, which can improve the selection space of data acquisition delay. In the ablation environment with helium, the electron number density of laser ablated plasma is relatively low, which can reduce the influence of Stark broadening effect and obtain narrower absorption lines, which is more conducive to the measurement of uranium atomic absorption spectrum. In order to reduce the influence of Doppler shift effect on absorption spectrum measurement and avoid misjudgment in spectrum analysis, it is more appropriate to carry out experimental measurement after 3μs sampling delay. Through experiments, the optimal conditions for measuring atomic absorption spectrum of uranium are obtained. Under these conditions, five different samples with &lt;sup&gt;235&lt;/sup&gt;U content of 4.95%, 4.10%, 3.00%, 1.10% and 0.25% respectively are measured, and the high-resolution absorption spectrum signals of &lt;sup&gt;235&lt;/sup&gt;U and &lt;sup&gt;238&lt;/sup&gt;U are obtained. The absorption spectra of samples with different content are measured and statistically analyzed, the &lt;sup&gt;235&lt;/sup&gt;U absorption signal has high linearity, the fitting correlation coefficient can reach 0.989, and the limit of detection is 0.033% (3σ). The stability test of absorption spectrum signal shows that the relative standard deviation of &lt;sup&gt;238&lt;/sup&gt;U, &lt;sup&gt;235&lt;/sup&gt;U and &lt;sup&gt;235&lt;/sup&gt;U / &lt;sup&gt;238&lt;/sup&gt;U signals are 2.054%, 2.152% and 0.524% respectively. The wavelength scanning mode is superior to the fixed wavelength spectrum measurement, and the influence of the energy fluctuation between different ablation pulses on the spectrum measurement is weakened by the wavelength scanning mode to a certain extent. The results show that laser ablation combined with absorption spectroscopy technology is suitable for uranium isotope ratio analysis and has great potential applications in rapid isotope analysis of nuclear fuel.&lt;/sec&gt;

Investigation of radionuclide contamination of materials stored in solid radwaste repository of the Chornobyl NPP

The composition and features of radionuclide contamination of solid radioactive waste (SRW) stored in the western “light” compartment of SRW repository (RSRW) of the SSE “Chornobyl Nuclear Power Plant” (ChNPP) were studied. Representative samples of SRW taken from the top layer of materials at 1-m depth were split into four streams, and according to their physical state, they were classified into two categories: combustible (one stream) and non-combustible (three streams) ones. After relevant sample preparation was carried out, the SRW samples were investigated in the ChNPP Laboratory for water-radiochemical measurement in order to identify the radionuclides, which are subject to compulsory certification according to SRW acceptance criteria valid in the Exclusion Zone. It was stated that SRW radioactivity levels in the upper layer of western “light” compartment of SWR are, mainly, determined by radionuclide contents of 137Cs, 60Co, 90Sr, 94Nb, 235U, 238U, 241Am, 3 H and 14C. The parameters of regression dependencies and correlation coefficients between the specific activity of radionuclides in stream- and integrated (for non-combustible SRW) data samples compiled of measurement results (above the minimally detectable activity) were estimated. It was stated that the features of radionuclide contamination spectrum of the SRW in western and eastern compartments are largely similar ones, that, apparently reflects the typical properties of the ChNPP operational wastes produced in period from 1978 to 1986, and which had been stored in mothballed state in the RSRW before the accident at the ChNPP Unit 4 occurred. However, for such radionuclides as 60Co, 94Nb and 90Sr, observable levels of SRW contamination in the western compartment are significantly higher, than in the eastern one. At the same time, the specific activity of uranium isotopes 235, 238U is several times lower. It was concluded that the experimental and analytical results obtained in this work can be used as the source data for the next stage of studies — calculation of scaling factors and determination of radionuclide vectors needed to certify the difficult-to-measure radionuclides in the ChNPP SRW packages being transported to their burial.

Radiochemical technique as a tool for determination and characterisation of El Sela ore grade uranium deposits

ABSTRACT The present study is an application of a radiochemical procedure for the determination of 238U, 235U and 234U as well as uranium isotopic ratios in El Sela ore grade samples that located at the Southeastern Desert of Egypt. This procedure is consisting of several steps include sample preparation, chemical separation and source preparation followed by counting using alpha-particle spectrometry technique. Radiochemical determination of various uranium isotopes contents indicated that El Sela uranium deposits are considered as a recent deposit where there was a large difference between radiochemically and radiometrically determined uranium. The measured 234U/238U activity ratios for most samples were approximately unity, indicating that secular radioactive equilibrium was established between 238U and 234U in the El Sela mineralised rocks. On the other hand, 238U and 234U might be equally leached due to the effect of rock-water interactions during the pluvial time by the action of surficial or underground water. The 238U/235U activity ratios of the studied mineralised granites were significantly shifted from the natural ratio 21.7, indicating that the redox conditions and alteration processes played an important role in the fractionation of 238U from 235U. The values of 234U/235U ratios in the studied granites varied between 23.08 and 34.70 in different samples, suggesting 235U migration out due to the prevailing conditions.

Recurrent deposition of organic-rich sediments in Early Triassic pelagic Panthalassa and its relationship with global oceanic anoxia: New data from Kyoto, Southwest Japan

Abstract The Early Triassic experienced one of the most extensive episodes of oceanic oxygen depletion in the Phanerozoic, which was considered to be reflected in the deposition of black organic-rich claystone and general absence of radiolarian chert in pelagic deep-water areas of Panthalassa. However, while studies of peri-continental sections demonstrate that oceanic anoxia repeatedly occurred throughout the Early Triassic, black claystone deposition was thought to be restricted to earliest Triassic times. In this paper, the lithostratigraphy, conodont biostratigraphy and chemical composition are investigated at two Olenekian–Anisian sections in Japan, deposited in pelagic deep-water areas of Panthalassa. Sedimentation rates and major element compositions support published findings that the absence of chert is a consequence of increased clastic input and not radiolarian extinction due to oceanic anoxia. Biostratigraphic correlation with previously described sections reveals that the deposition of extensive black claystone occurred in the Induan, early Spathian (early late Olenekian) and across the Olenekian–Anisian boundary. The three black claystone lithofacies are associated with sedimentary and geochemical evidence of anoxia in the water column and bottom waters. Organic-rich deposition is generally coeval with episodes of expanded anoxic seafloor as indicated by uranium isotopes, although they are decoupled in Smithian (early Olenekian) times. Black claystone of end-Olenekian to early Anisian age represents the first finding of a laterally extensive deposit associated with oceanic anoxia during this time interval. Results imply that the deposition of black organic-rich claystone in pelagic deep Panthalassa reflects global trends in the spatial extent of bottom water anoxia during the Early Triassic, probably controlled mainly by nutrient input to the oceans.

Radioactivity of Bottled Water from Trade Network in Kyiv

In 2018-2019, we examined the radioactivity of 40 samples of bottled water of popular brands produced both in Ukraine and abroad, which were purchased in one Kyiv supermarket. The first stage of the study provided for the identification of total alpha and total beta activities. In the case of excessing their regulated values, we proceeded to the determination of the content of radium-226 and natural mixture of uranium isotopes. The study results evidenced that total alpha and total beta activities of low mineralization water do not exceed the regulated values. Total alpha activity exceeded the regulated value of 0.1 Bq/l ten times in specific cases and total beta-activity exceeded the value of 1.0 Bq/l almost three times for the majority of high mineralization water brands.&#x0D; The results of measuring total alpha and total beta activities depending on time elapsed from the moment the sample was prepared to the start of the measurements showed an increase in the alpha activity over time is typical for individual water samples, which indicates the accumulation of radioactivity from radium-226 decay products. However, the results of measuring the activity of radium-226 and a natural mixture of uranium isotopes did not reveal cases of exceeding regulated levels, which allows considering water of all brands suitable in terms of radionuclide content.&#x0D; Assessment of radiation doses from consumption of bottled water containing the measured values of radium-226 and natural mixture of uranium isotopes did not reveal exceeding regulated value of 0.1 mSv/year. Only one bottled water brand was an exception, since the estimated radiation dose for it was 0.2 mSv/year for the category of children aged 12 to 17 years with 98 % of its value due to radium-226. Such a radiation dose value was received assuming an annual consumption of 1.5 liters per day.

Uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes

This paper studies the uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes from 52 groundwater samples in the province of Granada (Betic Cordillera, southeastern Spain). According to the geological complexity of the zone, three groups of samples have been considered. In Group 1 (thermal waters; longest residence time), the average uranium content was 2.63 ± 0.16 μg/L, and 234U/238U activity ratios (AR) were the highest of all samples, averaging 1.92 ± 0.30. In Group 2 (mainly springs from carbonate aquifers; intermediate residence time), dissolved uranium presented an average value of 1.34 ± 0.13 μg/L, while AR average value was 1.38 ± 0.25. Group 3 comes from pumping wells in a highly anthropized alluvial aquifer. In this group, where the residence time of the groundwater is the shortest of the three, average uranium content was 5.28 ± 0.26 μg/L, and average AR is the lowest (1.17 ± 0.12). In addition, the high dissolved uranium value and the low AR brought to light the contribution of fertilizers (Group 3). In the three groups, 235U/238U activity ratios were similar to the natural value of 0.046. Therefore, 235U detected in the samples comes from natural sources. This study is completed with the determination of major ions and physicochemical parameters in the groundwater samples and the statistical analysis of the data by using the Principal Component Analysis. This calculation indicates the correlation between uranium isotopes and bicarbonate and nitrate anions.

Application of plasma mass spectrometry for half-life measurement of medium and long-lived radionuclides

When combined with established primary counting techniques, atom counting using inductively coupled plasma mass spectrometry (ICP-MS) can be a powerful metrological tool for providing updated, precise half-life values for medium and long-lived radionuclides, giving end-users increased confidence in measurement for a range of nuclear applications. ICP-MS is increasingly being used for this application, and this study outlines the methods for atom counting using the latest generation tandem ICP-MS/MS. The aim is to provide a consistent methodology that is currently lacking, and attention is paid to the importance of interference removal and minimising uncertainties, with preliminary results given for uranium isotopes.

Mass Distribution of the Fission Products of Plutonium Isotopes as Calculated by Using a Semi-empirical Model

The fission product yields (FPYs) of plutonium isotopes induced by thermal, 500-keV and 2-MeV neutrons are calculated by using a semi-empirical model recently developed and applied to uranium isotopes. In this model, the FPYs are assumed to be proportional to the level density of a compound nucleus at the fission barrier. The fission barrier height that determines the level density is modeled as a sum of a macroscopic term and four microscopic terms. The model has ten parameters, four of which are taken to be the same as those fixed for the uranium isotopes. The remaining six parameters are adjusted to reproduce the FPYs of plutonium isotopes. The resulting parameters for the plutonium isotopes are discussed in comparison with those for the uranium isotopes. The calculated FPYs are compared with experimental and evaluated data, as well as the calculation results from other fission models such as GEF and TALYS. Our semi-empirical model is shown to reproduce the overall features of the FPYs of plutonium isotopes.

Adaptation of the model method for estimating sample uncertainty

This approach to assessing the uncertainty of measurements of sample activity was developed taking into account the requirements of the laboratory for dosimetry of incorporated radionuclides within the framework of the Methodology for measuring the activity of uranium isotopes by the spectrometric method after extraction-chromatographic isolation from urine samples. A detailed analysis of the sources of uncertainties in the activity of the sample was carried out: the uncertainty of the chemical yield, the uncertainties in the measurements of the activity of the sample, the working radioactive solution (WRS), and the uncertainty in the volume. All uncertainties are divided into two types: type A and type B. Estimation of measurement uncertainty is based on a model approach. The procedure for estimating the uncertainty of the activity of the sample was successfully verified using the specialized software GUM Workbench Pro during their construction.

Improvement in the particle collection method to mitigate the mixing effect during uranium isotope analysis of environmental samples using secondary ion mass spectrometry

We introduce an improved particle collection method for uranium isotopic analysis using secondary ion mass spectrometry (SIMS). A new design was applied to a vacuum-suction impactor to promote the dispersibility of collected particles and the air flow rate was adjusted to maximize the particle recovery yield. The improved method remarkably mitigated the ‘mixing effect’. Materials from a nuclear forensic exercise were also employed to evaluate the method applicability. This innovation will be useful to improve the accuracy of SIMS uranium particle analysis, especially for overloaded samples with mixed isotope compositions.