Nuclide Ratios Research Articles

Nondestructive and destructive assay for forensics characterization of weapons-grade plutonium produced in LEU irradiated in a thermal neutron spectrum

A post-irradiation examination (PIE) of an enriched uranium sample was performed to advance a nuclear forensics methodology, based on intra-elemental nuclide ratios. The PIE was carried out on a few milligrams of low enriched uranium dioxide (LEUO2) sample, irradiated to a burnup of 1 GWd/MTU. The PIE of the LEUO2 sample provided the concentration of selected plutonium and fission product nuclides (239Pu, 240Pu, 241Pu, 91Y, 95Zr, 95Nb, 103Ru, 133Cs, 134Cs, 135Cs, 137Cs, 136Ba, 138Ba, 140Ba, 140La, 141Ce, 144Ce, 149Sm, 150Sm, 152Sm, 153Eu, and 154Eu). The PIE supported validation of the MCNP (Monte Carlo N-Particle neutronics simulation code) predicted concentration of these nuclides in the irradiated LEUO2 sample. This study showed that most of the MCNP predicted nuclide concentrations were within 15% and several within 10% compared to the PIE results. Gamma and mass spectrometry of nuclides in irradiated LEUO2 enabled the determination of uranium burnup and time since irradiation.

CRITICAL EXPERIMENT OF THORIUM LOADED THERMAL CORES AT KUCA (1) A NEW CRITICAL EXPERIMENT OF THORIUM LOADED CORE WITH HARDER NEUTRON SPECTRUM IN KUCA

In order to perform integral evaluation of 232Th capture cross section, a series of critical experiments for thorium-loaded and solid-moderated cores in KUCA had been carried out. In these experimental cores, H/235U nuclide ratio ranged about from 150 to 315, and 232Th/235U nuclide ratio ranged about from 13 to 19. In this study, a new critical experiment with Th loaded core in KUCA, which had about 70 of the H/235U ratio and 12.7 of 232Th/235U ratio, was carried out. As results, the excess reactivity was 0.086 ± 0.003 (% dk/k) and the keff was 1.0009 ± 0.0003, where the effective delayed neutron fraction was 7.656E-3. The keff was also calculated by MVP3.0 with different nuclear libraries. The respective calculations with JENDL-4.0, JENDL-3.3 and ENDF/B-VII.0 lead to 1.0056 ± 0.0086 (%), 1.0048 ± 0.0085 (%) and 1.0056 ± 0.0086 (%).On the other hand, the further MVP3.0 calculations, where only the 232Th cross sections were taken from JENDL-4.0, JENDL-3.3 or ENDF/B-VII.0 but all other nuclides were done from JENDL-4.0, were carried out to examine an impact of the difference of 232Th cross section among these nuclear libraries to the keff. The keff calculated with respective 232Th cross sections from JENDL-3.3 and ENDF/B-VII.0 was 1.0038 ± 0.0086 (%) and 1.0040 ± 0.0086 (%).

A homogeneous liquid reference material for monitoring the quality and reproducibility of in situ cosmogenic 10Be and 26Al analyses

Analysis of the in situ produced cosmogenic nuclides 10Be and 26Al has been used for several decades to study Earth surface processes; yet, no reference material has been widely adopted and used by the community to ensure the quality and comparability of sample preparation and isotopic analyses. Such a reference material could facilitate inter-laboratory comparison and serve as a benchmark for quantifying the accuracy, precision, and long-term reproducibility of terrestrial cosmogenic nuclide analyses. Here, we describe a liquid reference material, UVM-A, which is freely available to the community. We created four liters of solution by dissolving CRONUS-A granular reference material [1], and spiking the solution with stable 9Be and 27Al, yielding a solution containing 236.7 ± 0.6 μg g−1 Be and 932.6 ± 1.6 μg g−1 Al (average, 1SD). Initial analyses of UVM-A indicate that the nuclide ratios of the reference material (10Be/9Be 1.43 ± 0.02 × 10−13; 26Al/27Al 4.44 ± 0.05 × 10−13; average, standard error) are similar to those of late-glacial exposure samples, are tightly clustered, and match the nuclide concentrations expected from the CRONUS-A quartz used to prepare the reference material. Use of this reference material will help to quantify uncertainty in cosmogenic exposure ages, burial ages, and erosion rates resulting from sample preparation and isotopic analysis.

Natural nickel as a proton beam energy monitor for energies ranging from 15 to 30 MeV

The degradation of proton beam energy within a target stack was monitored via product nuclide ratios at the Los Alamos Isotope Production Facility (LANL-IPF). Nuclear reaction channels employed as energy monitors included NatNi(p,x)57Co and NatNi(p,x)57Ni. Natural nickel foils (thicknesses 0.025 mm) were used to determine proton beam energies ranging from 15 to 30 MeV. Energy values were estimated from a fitted 57Ni/57Co production activity ratio curve, which, in turn, was calculated from formation cross section data. Isotope production yields in the low energy “C” slot at LANL-IPF are very sensitive to beam energy, and differences of several MeV can translate into a drastic effect on overall production yields and radiochemical purity. Proton energies determined in this target stack position using nickel foils will serve as a basis to optimize radionuclide production in terms of product yield maximization and by-product minimization.

An evidence of chemically and physically mediated migration of 238U and its daughter isotopes in the vicinity of a former uranium mine

The present study reports the evidence of a radioactive contamination in a wetland located downstream from a former French U mine in Brittany. This situation is demonstrated according to the measurements of gamma dose rates and activity ratios of 238U and 232Th-decay series nuclides, which give the justification regarding the accumulation of significant amounts of 238U, 230Th and 226Ra in this wetland.The dose rate map highlights an increase of radiation level along the former mine water pathway compared to the background value, with a maximum value of 1500 nSv.h−1 reached in the wetland. Activities of 238U, 230Th and 226Ra and 232Th/238U ratios measured in surface wetland soils are significantly higher than the geochemical background. 230Th/238U ratios less than unity suggest a preferential accumulation of U in the wetland, compared to its daughter isotopes. Moreover, the loss of 226Ra compared to 230Th raises its higher mobility compared to its parent isotope. In far-field sediments, 226Ra/238U ratio of 1.76 implies a different geochemical behavior of U, which could be explained by the occurrence of mobile U species. The results suggest that contamination of wetland soils and far-field sediments could result from discharges of underground mine waters.

Source term estimation of multi‐specie atmospheric release of radiation from gamma dose rates

Determination of a source term of an accidental release of radioactive material into the atmosphere is very important for evaluating emergency situations and their consequences. However, knowledge of the source term and its composition is typically vague and uncertain. One possible way to obtain the source term is inverse modeling in which an atmospheric transport model is combined with field measurements. The most accessible measurements are those from gamma dose rate (GDR) detectors. However, GDR measurements represent a sum of contribution from all nuclides from both plume and deposition which makes the problem particularly difficult. The same difficulty arises when the measurements can not distinguish contribution from another species in the release, such as nuclides attached to different particle sizes. We propose a Bayesian method for recovery of the source term from GDR measurements where a priori knowledge on ratios of different species is given in the form of bounds. This knowledge is incorporated into the model of covariance matrix of the source term. The Bayesian methodology allows to handle uncertain knowledge on the nuclide ratios as well as unknown temporal correlations of the source term. We evaluate and compare the proposed method with other state‐of‐the‐art methods on a twin experiment of a non‐stationary release of 16 nuclides from the Czech nuclear power plant Temelin being registered by the Austrian GDR monitoring network. Real‐world validation of the approach is performed on the latest measurements of concentration and deposition of caesium‐137 from the Chernobyl accident, where we estimate composition of the source term from different particle sizes (species). The estimated source term is in very good agreement with previously reported results and the calculated species ratios are supported by the available observations.

Challenges in constraining ages of fluvial terraces in the Vienna Basin (Austria) using combined isochron burial and pIRIR225 luminescence dating

Burial dating with terrestrial cosmogenic nuclides and luminescence dating techniques have become two powerful tools to temporally constrain Quaternary deposits. A combination of both methods at the same geological setting has rarely been realized to date, although their viable time frames overlap by several tens of thousands of years. When Middle Pleistocene sediments with depositional ages ranging around ca. 120 ka to ca. 300 ka are targeted, both methods are employed, but come towards their lower and upper limits, respectively. A combined dating approach can be worthwhile at this age range and allows not only exploring the edges of both methods, but holds the opportunity to do a cross-check of results at an age spectrum, where both dating techniques are at risk to become fuzzy.Here we present a case study where numerical ages of two Middle Pleistocene terraces located in the Vienna Basin were generated by combining burial and luminescence dating. A variety of processes, such as changing sediment input rates, erosion, and tectonics controlled the formation of fluvial terraces in the basin and shaped its complex modern surface. Age correlation of the evolved mosaic of blocks and dislocated sediment bodies is challenging and requires quantitative geochronological information in order to establish a coherent terrace stratigraphy. Luminescence and burial samples originating from two fluvial terraces, the lower Gaenserndorf terrace (GDT) and the higher Schlosshof terrace (SHT), were analyzed and evaluated. Luminescence and burial ages at the GDT site are in good agreement and suggest a depositional age of 140 ± 170 ka bracketed by pIRIR225 luminescence ages ranging from 120 ± 10 ka to 260 ± 30 ka. Luminescence samples at the SHT site are in saturation, but provide minimum ages, which are coherent with the burial dating result of 340 ± 170 ka. The new numerical ages indicate that the vertical offset between the GDT site and the SHT site was not purely caused by fault activity, but suggest two independent episodes of sediment accumulation.Besides providing new insights into the stratigraphic and morphological configuration of the central Vienna Basin area, the cosmogenic nuclide data set is compelling from a methodological point of view. At the GDT site, several samples exhibited 26Al/10Be nuclide ratios exceeding the surface production ratio of 6.75. Even though affected samples were excluded from burial age calculations, a detailed investigation on possible scenarios, which could have caused an upwards shift of 26Al/10Be ratios, was carried out.

Delayed gamma-ray spectroscopy combined with active neutron interrogation for nuclear security and safeguards

For the purpose of nuclear security and safeguards, an active neutron interrogation non-destructive assay technique, Delayed Gamma-ray Spectroscopy (DGS), is under development. The technique of DGS uses the detection of decay γ rays from fission products to determine ratios of fissile nuclides in a sample. A proper evaluation of such γ-ray spectra requires integration of nuclear data such as fission cross-sections, fission yields, half-lives, decay-chain patterns, and decay γ-ray yields. Preliminary DGS experiments with the Pulsed Neutron Interrogation Test Assembly, named PUNITA, of the European Commissions’ Joint Research Center have been performed. Signals of delayed γ ray from nuclear materials were successfully observed.

On the calculation of activity concentrations and nuclide ratios from measurements of atmospheric radioactivity

Motivated by the need for consistent use of concepts central to the reporting of results from measurements of atmospheric radioactivity, we discuss some properties of the methods commonly used. Different expressions for decay correction of the activity concentration for parent–daughter decay pairs are presented, and it is suggested that this correction should be performed assuming parent–daughter ingrowth in the sample during the entire measurement process. We note that, as has already been suggested by others, activities rather than activity concentrations should be used when nuclide ratios are calculated. In addition, expressions that can be used to transform activity concentrations to activity ratios are presented. Finally we note that statistical uncertainties for nuclide ratios can be properly calculated using the exact solution to the problem of confidence intervals for a ratio of two jointly normally distributed variables, the so-called Fieller׳s theorem.

The Effect Assessment for Fast Reactor Fuel Cycle Deployment-improvement of the Assessment Method-

The energy economic model has been developed to assess long term socio-economic effects, resulting from the deployment of economic competitive fast reactors (FR) with innovative technologies. The model is comprised of a recursive dynamic Computable General Equilibrium (CGE) model based on GTAP-E, an energy environmental version of the “Global Trade and Analysis Project (GTAP)” model and a dynamic linear optimization type energy system model called “Dynamic New Earth 21 (DNE21)” model. By the coordination of these models, the socio-economic effects on the world could be calculated from needed input data, e.g. population, industrial structure, reference GDP, reference demand of energy, energy technology and fuel cycle cost.In this study, the energy economic model was upgraded to assess the socio-economic effects in the world by dividing into eighteen countries/region including Japan, China, South Korea, and other in Asia. The model also was upgraded to calculate plutonium constrains to derive the FR capacity in detail. Specifically, the function of burnup calculation, using the loading fuel composition and the matrix which indicates the radionuclide transition ratio for each nuclide in the fuel, was added. The matrix was made for forty-seven actinide nuclides composing the loading fuel. The neutron flux and fission reaction of each nuclide were calculated by ORIGEN code to make the matrix, and the normalized value, each nuclide ratio divided by total mass of nuclide, was used as each component of the matrix. Although, the calculated FR capacity by the previous version was increased to the upper limit of input capacity, the calculated capacity by the upgraded model was constrained by plutonium feed. As a result, more accurate FR capacity in the world was assessed in the model.Moreover, based on the assessment results for FR deployment by the energy economic model, the effects of FR exports were assessed. Specifically, it was assumed that the final demand of related industry was increased by the FR exports. Based on the final demand and self-sufficient rate, the domestic demand could be calculated. The domestic demand will spur demand in two ways. One way is the increased intermediate demand of raw materials to fill the domestic demand, other way is the consumption increased effect caused by the increased compensation of employment. As a result of calculating these demands, direct effect of the FR export could be clarified. Also, primary and secondary indirect ripple effects could be calculated from the direct demand. The former is the induced production in related industries to fill the increased intermediate demand of raw materials, the latter is also induced production caused by the increased compensation of employment to fill intermediate demand of raw material and secondary indirect effect. Thus, these indirect ripple effects and direct effect were calculated as the effect of FR exports.

Constant cosmogenic nuclide concentrations in sand supplied from the Nile River over the past 2.5 m.y.

Quartz sand in the eastern Mediterranean coastal plain is supplied through an extended transport system, which includes the Nile River, east Mediterranean longshore currents, and inland eolian transport. While the concentrations of cosmogenic nuclides ( 26 Al and 10 Be), and their ratio, in modern sand deposited along the coast of the eastern Mediterranean reflect the combined effect of exposure and burial during transport, the concentrations of these nuclides in buried sands are the result of decay of this initial dosing. Samples of modern exposed sand (n = 3) collected from the coastal plain of Israel yield an average 26 Al/ 10 Be ratio of 4.8 ± 0.2, significantly lower than the expected ratio of 6.8 for exposed quartz grains at the surface. A similar ratio of 4.5 ± 0.3 was measured in a late Pleistocene sand sample, indicating similar exposure-burial histories during transport in spite of the difference in climatic conditions. The results imply a steady, preburial cosmogenic nuclide ratio related to the Nile River9s ability, through storage and recycling, to buffer the effects of climatic and tectonic perturbations on cosmogenic nuclide concentrations in the transported quartz. All ancient and buried sand samples (n = 11) fall on a decay path that originates from the concentrations and ratio of 26 Al and 10 Be in modern sand, suggesting steady preburial concentrations of cosmogenic nuclides in quartz sand over the past 2.5 m.y.

DECSERVIS-2: A tool for natural decay series mass flow simulation

After the publication of “DECSERVIS: a tool for radioactive decay series visualisation” we have further developed our DECSERVIS software. With the new tool DECSERVIS-2 one can simulate radioactive decay chains in open systems, i.e. when the concentrations of nuclides change also due to mass flows. Decay chains can be simulated under continuous and successive nuclide mass flow events into and out from the system and in freely determined time intervals. Simulation output for the entire decay chain (nuclide activity, mass, number of nuclides, nuclide ratios) can be presented as a function of time with various graphical presentations such as solid curve and column diagrams or animation. In this paper we introduce DECSERVIS-2 and demonstrate its use with simulation examples. DECSERVIS-2 is easy to use and has been designed with an eye on the demands of teaching.

A new approach to estimate nuclide ratios from measurements with activities close to background

Measurements of low-level radioactivity often give results of the order of the detection limit. For many applications, interest is not only in estimating activity concentrations of a single radioactive isotope, but focuses on multi-isotope analyses, which often enable inference on the source of the activity detected (e.g. from activity ratios). Obviously, such conclusions become questionable if the measurement merely gives a detection limit for a specific isotope. This is particularly relevant if the presence of an isotope, which shows a low signal only (e.g. due to a short half-life or a small transition probability), is crucial for gaining the information of interest. This paper discusses a new approach which has the potential to solve these problems. Using Bayesian statistics, a method is presented which allows statistical inference on nuclide ratios taking into account both prior knowledge and all information collected from the measurements. It is shown that our method allows quantitative conclusion to be drawn if counts of single isotopes are low or become even negative after background subtraction. Differences to the traditional statistical approach of specifying decision thresholds or detection limits are highlighted. Application of this new approach is illustrated by a number of examples of environmental low-level radioactivity measurements. The capabilities of our approach for spectrum interpretation and source identification are demonstrated with real spectra from air filters, sewage sludge and soil samples.

Nuclide ratios and source identification from high-resolution gamma-ray spectra with Bayesian decision methods

Ratios of radionuclide activity concentrations are often used to identify sources of small traces of radioactivity in environmental samples. A new approach is presented to consider statistical uncertainties and their impact on decisions based on nuclide ratios particularly for cases where nuclide ratios are calculated from measurements close to or below detection limit. It is pointed out that decision threshold and detection limit are adequate for decisions on the presence of a single nuclide but not necessarily on decisions on nuclide ratios. A statistical analysis based on a Bayesian approach is presented which allows inference on probabilities of nuclide ratio values taking into account jointly the information available for all radionuclides of interest. Examples are discussed to demonstrate the improvements of this approach in spectrum analysis and in source identification. As an important case the detection of Xenon isotopes ( 135Xe, 133mXe, 133Xe and 131mXe) that are relevant for detecting underground nuclear explosions in the context of the verification of the Comprehensive Nuclear Test-Ban Treaty (CTBT) is discussed. Nuclide ratios are crucial in order to distinguish civil releases from CTBT-relevant sources. A new method is presented for graphical evaluation of the xenon isotope measurements and for assigning potential sources using the statistical approach proposed in this paper.

Total deposition velocities and scavenging ratios of 7Be and 210Pb at Rokkasho, Japan

The atmospheric concentrations and deposition fluxes of 7Be and 210Pb were observed biweekly in Rokkasho, Japan on the Pacific Ocean coast at the northern end of Honshu Island, from March 2000 to March 2006, to clarify their regional features. Seasonal variation pattern of atmospheric 7Be concentrations had double peaks, and that of 210Pb had a single peak. Deposition fluxes of 7Be and 210Pb showed the same patterns. The total deposition pattern of 7Be was similar to that commonly seen on the Pacific Ocean side of northern Honshu Island, while the pattern of 210Pb was similar to that commonly seen on the Japan Sea side. The lack of high spine mountains windward in Rokkasho may be the cause of this ambiguity in the winter monsoon season. Total deposition velocities and scavenging ratios of 210Pb were similar to those of 7Be from spring to fall, and showed that both nuclides had a similar removal process from the atmosphere. However, the scavenging ratios of 210Pb were slightly larger than those of 7Be in winter, indicating different behaviors for both nuclides in the scavenging process. The scavenging ratios of both nuclides inversely correlated with precipitation rate, and the ratios in winter were larger than in the other seasons.

Analyzing Nuclear Fuel Cycles from Isotopic Ratios of Waste Products Applicable to Measurement by Accelerator Mass Spectrometry

An extensive study was conducted to determine isotopic ratios of nuclides in spent fuel that may be utilized to reveal historical characteristics of a nuclear reactor cycle. This forensic information is important to determine the origin of unknown nuclear waste. The distribution of isotopes in waste products provides information about a nuclear fuel cycle, even when the isotopes of uranium and plutonium are removed through chemical processing. Several different reactor cycles of the pressurized water reactor, boiling water reactor, Canada deuterium uranium reactor, and liquid-metal fast breeder reactor were simulated for this work with the ORIGEN-ARP and ORIGEN2.2 codes. The spent-fuel nuclide concentrations of these reactors were analyzed to find the most informative isotopic ratios indicative of irradiation cycle length and reactor design. Special focus was given to long-lived and stable fission products that would be present many years after their creation. For such nuclides, mass spectrometry analysis methods often have better detection limits than classic gamma-ray spectroscopy. The isotopic ratios 151Sm/146Sm, 149Sm/146Sm, and 244Cm/246Cm were found to be good indicators of fuel cycle length and are well suited for analysis by accelerator mass spectroscopy.

Numerical evaluation of nuclide analysis of I129, Sr90, and Cs137 using bremsstrahlung high energy x ray generated by ultrashort pulse laser

We analyzed numerically the feasibility of nuclide analysis of spent fuels using an ultraintense, ultrashort laser. The (γ,n) reaction yields for each nuclide such as I129, Sr90, and Cs137 were calculated using the bremsstrahlung spectrum and the nuclear reaction cross sections. The dependence of the (γ,n) reaction yield on the irradiation time was derived. We also calculated the dependence of the nuclide ratio on the bremsstrahlung photon temperature. In order to investigate the influence of electron temperature and target thickness on the bremsstrahlung photon spectrum, the calculations were performed using the Monte Carlo code GEANT4. When gold was used as bremsstrahlung converter target at a temperature of the incident electrons of 30MeV, the target thickness providing maximum nuclear reaction yield was found to be 5mm.

1183. 測定誤差と核種組成の不確定性に対するクリアランスレベル検認の安全裕度の考え方

On the monitoring for compliance with clearance level, the concentrations of objective nuclides, such as alpha or lowenergy beta emitters, can be estimated without direct gamma measurement by assuming the existence of objective nuclides with geometric mean concentrations or using previously assessed information on nuclide spectra and measurement results for a key gamma nuclide. To determine whether clearance can be carried out, deviations in the mean concentrations and nuclide ratios to the key gamma nuclide should be appropriately considered, in addition to the measurement error. In this paper, the concept of clearance level has been reconsidered and a new approach has been proposed to establish an appropriate safety factor of the monitoring for compliance with clearance level. To apply the approach to practical use, a probability distribution calculation system has been developed and verified. A simple method has also been proposed to determine whether the safety factor is required. The other option is to adopt initially a conservative value for the mean concentrations or the nuclide ratios. It has also been clarified that the use of arithmetic means for the mean concentrations or the nuclide ratios is more conservative than the present approach.

Plutonium and americium in the sediments off the Thule air base, Greenland

In 1968 a U.S. B-52 bomber from USA with four nuclear weapons crashed on the sea ice near the Thule air base and contaminated the surroundings. Most of contamination was recovered during the cleanup program. However, some of the plutonium still remains in the bottom sediments of the area. In 1997 an international expedition with a comprehensive sampling program was performed. A lot of sediment samples were taken with a Finnish Gemini corer. Sediment samples from 5 sampling stations, 80 samples altogether, were pretreated in Risř, Denmark, and analysed for transuranic elements at STUK, Finland. The samples were analysed primarily for Pu, but gamma-spectrometric measurements of 241Am were also made. Generally, the Pu concentrations in the area studied were from 1 to 3 magnitudes higher than the fallout level in the Arctic sea area. None of the vertical profiles of Pu at the various stations showed a typical Pu peak originating from the accident in 1968, but the sediments were mixed down and contaminated to the depths studied (20 cm). The presence of large quantities of hot particles distorted the estimations of mean concentrations and inventories. Samples with plutonium from the accident show significant variations of nuclide ratios, 238Pu/239,240Pu, 241Pu/239,240Pu and 241Pu/241Am. This indicates that Pu at Thule may be from more than one source of different quality.

The distribution of artificial radionuclides in the waters of the Norwegian-Greenland Sea in 1985

In the summer of 1985, sea water samples were taken to determine 3H, 90Sr, 134Cs, 137Cs and transuranics within a grid of 165 stations including 16 depth series down to the seafloor, covering all ice-free areas. The distribution of the activity concentrations and the nuclide ratios reveal the contamination pathway into the surface and deeper layers of the Norwegian-Greenland Sea from nuclear weapon fallout and civil nuclear technology. Moreover, the investigations show that: (1) a yearly discharge of 1 TBq (10 12 Bq) 90Sr into the Irish Sea (English Channel) is diluted on its way to the southern Norwegian Sea, raising the concentration by about 0.04 mBq l −1; (2) the drift time to this sea area is around 4 years; (3) about 40% of the 137Cs discharged does not reach the Norwegian Sea and (4) a further 30% leaves the Norwegian-Greenland Sea via the North Cape and flows into the Barents Sea. Investigations into the vertical distribution and stratification of the radioactivity indicate the time scale on which the radionuclides travel to the deeper layers.