<Superscript>234</Superscript>U/<Superscript>235</Superscript>U activity ratios as a probe for the <Superscript>238</Superscript>U/<Superscript>235</Superscript>U half-life ratio

High-resolution alpha-particle spectrometry was performed on three uranium materials enriched in ²³⁵U. Besides the ²³⁵U peaks, separate peaks belonging to impurity traces of ²³⁴U could be quantified. Relying on the isotopic composition of the uranium, as determined by mass spectrometry, the ratio of the half-lives of ²³⁸U and ²³⁵U was determined via the activity ratio of ²³⁴U and ²³⁵U in the materials. As an intermediate link, the ²³⁴U/²³⁸U half-life ratio was taken from published mass spectrometric analyses of ‘secular equilibrium’ uranium material. The resulting half-life ratio T _1/2(²³⁸U)/T _1/2(²³⁵U) = 6.351±0.031 is in agreement with the commonly adopted half-life values determined by Jaffey et al.     

Improvement in precision of extremely low <Superscript>236</Superscript>U/<Superscript>238</Superscript>U isotope ratio determination by using mass spectrometer with narrow dynamic range

The precision in measurement of trace level uranium isotopic ratio, i.e., ²³⁶U/²³⁸U or ²³⁴U/²³⁸U, on single Faraday detector with narrow dynamic range is very hard to achieve. this is mainly due to the narrow dynamic range of a single detector systems. A significant improvement in mass spectrometric determination of ²³⁶U/²³⁸U ratio has been achieved by employing an alternate method using a single Faraday detector of narrow dynamic range. The method makes use of the precise measurements of the ²³⁶U/²³⁴U ratio, ²³⁴U/²³⁵U ratio and ²³⁵U/²³⁸U ratio, which are used to calculate the ²³⁶U/²³⁸U ratio using the equation ²³⁶U/²³⁸U=²³⁶U/²³⁴Uײ³⁴U/²³⁵Uײ³⁵U/²³⁸U. Despite the fact that correlation of the data tends to increase the uncertainty in the result, our results show a significant improvement, i.e., more than 8 times better precision in measuring the ²³⁶U/²³⁸U ratio with this method (σ=3.98×10⁻⁰⁸) as compared to direct measurement of ²³⁶U/²³⁸U (σ=3.104×10⁻⁰⁷). The method widens the applicability of the single collector system with narrow dynamic range and it will potentially be helpful to improve the precision in the case of the static multi-collector system also. The objective of the present study was to compare the results of the same sample analyzed with the present alternate method and the direct method for precision.     

Disequilibrium of dissolved <Superscript>234</Superscript>U/<Superscript>238</Superscript>U and <Superscript>210</Superscript>Po/<Superscript>210</Superscript>Pb in Greek rivers

For the first time, a radiological study for the dissolved ²³⁸U, ²³⁴U, ²¹⁰Pb and ²¹⁰Po was held in major Greek rivers across the country. ²³⁴U/²³⁸U activity ratios are above one in all samples and ²¹⁰Po/²¹⁰Pb activity ratios are respectively below the unit indicating the disequilibrium in the samples. Quite satisfactory correlations were observed among ²³⁴U and ²³⁸U as well as among ²¹⁰Po and ²¹⁰Pb values. Uranium isotopes were separated by ion exchange and electroplated on stainless steel plates. ²¹⁰Po was spontaneously deposited on nickel plates, while ²¹⁰Pb was indirectly determined through the ingrowth of ²¹⁰Po. The sources were measured by a-spectrometry.     

Comparison of analytical methods used to determine <Superscript>235</Superscript>U, <Superscript>238</Superscript>U and <Superscript>210</Superscript>Pb from sediment samples by alpha,beta and gamma spectrometry

An intercomparison of the methodology (alpha, beta and gamma spectrometry) used for ²³⁸U, ²³⁵U and ²¹⁰Pb determination was carried out based on 38 sediment samples. The activity range of the samples varied from 10–700 Bq/kg for ²¹⁰Pb, 1–35 Bq/kg for ²³⁵U and 10–800 Bq/kg for ²³⁸U. Results obtained using the three methods were not statistically different at high activity levels, but agreement between the results decreased at lower sample activity levels. For ²¹⁰Pb, the smallest difference was found between alpha and gamma spectrometry. A good correlation between results from alpha and gamma spectrometry was observed over the whole activity range. In beta spectrometry, the results were slightly higher than those obtained by alpha or gamma spectrometry due to the impurity of ²²⁸Ra. In ²³⁸U analysis, good correspondence was observed between ²³⁸U determined by gamma and alpha spectrometry, particularly at higher ²³⁸U activity concentrations over 100 Bq/kg. In ²³⁵U analysis, attention needs to be paid to interference from ²²⁶Ra and its reduction.     

Behavior of uranium along Jucar River (Eastern Spain): Determination of234U/238U and235U/238U ratios

The uranium concentration and the²³⁴U/²³⁸U,²³⁵U/²³⁸U activity ratios were studied in water samples from Jucar River, using low-level -spectrometry. The effects of pH, temperature and salinity were considered and more detailed sampling was done in the neighbourhood of Cofrentes Nuclear Plant (Valencia, Spain). Changes were observed in the uranium concentration with the salinity and the²³⁴U/²³⁸U activity ratio was found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes in the concentration of uranium and the activity ratios.     

A combined method of neutron activation analysis and radiometric measurements for <Superscript>234</Superscript>U and <Superscript>238</Superscript>U determination in soil samples of low uranium concentration

A method that combines the use of non-destructive neutron activation analysis and high-resolution α spectrometry has been developed for determination of the activities of ²³⁴U and ²³⁸U in geological samples of low uranium content. The ²³⁸U content is determined by k₀-based neutron activation analysis, whereas the ²³⁴U/²³⁸U relationship is measured by α spectrometry after isolation and electrodeposition of the uranium extracted from a lixiviation with 6 M HCl. The main advantage of the method is the simplicity of the chemical operations, including the fact that the steps destined to assure similar chemical state for the tracer and the uranium species present in the sample are not necessary. The method was applied to soil samples from sites of the North Peru Coast. Uranium concentration range 3–40 mg/kg and the isotopic composition correspond to natural uranium, with about 10% uncertainty.     

Fast evaluation of <Superscript>235</Superscript>U/<Superscript>238</Superscript>U ratio in nuclear spent fuel safe guard by thermal ionization mass spectrometry by using refractory metal oxides

A direct simple and fast method was established, to overcome the influence of low and high level impurities on the measurement of ²³⁵U/²³⁸U isotopic ratio in nuclear spent fuel safeguard by thermal ionization mass spectrometry (TIMS), by using refractory metal oxide. The addition of refractory metal oxides forming solution (RMOFS), in certain proportions alongside with the spent fuel solution on the sample filaments were found to be useful during the analysis of uranium isotopic ratio by TIMS. RMOFS (with oxide melting point exceeding 2,000 °C), and particularly that of magnesium, were found to be very effective in improving the quality of the ion signal of ²³⁵U and ²³⁸U, when added without the need for prior purification. Solutions of chromium, cerium, thorium, and magnesium were investigated, to select the more convenient one, and it was found that magnesium was very useful to start with. The method was very simple, improve both the accuracy and precision of the collected data, reduce the time required to achieve steady uranium pilot signal, and hence the over all time of the analysis, regardless of the level of impurities present.     

222Rn content and234U/238U activity ratio in groundwaters

Geochemical radioanalytical studies of groundwater were performed in the valleys of Villa de Reyes and San Luis Potosi (Mexico). The experiments were designed to measure radon and uranium content and²³⁴U/²³⁸U activity ratio in groundwater samples taken from wells in these sites and at the Nuclear Center of Salazar, Mexico.²²²Rn content varied depending on the sample source, reaching a maximum value of 235 pCi/l; uranium concentration results were less than 1 g/1 and²³⁴U/²³⁸U activity ratios were close to equilibrium.     

Measurement of the <Superscript>231</Superscript>Pa/<Superscript>235</Superscript>U ratio for the age determination of uranium materials

The paper describes the age (production date) determination of uranium reference materials using the ²³¹Pa/²³⁵U ratio. Direct addition of ²³⁷Np in secular equilibrium with its ²³³Pa daughter was chosen instead of the regular milking of ²³⁷Np to avoid possible loss of Pa. Sample preparation consists of a fast, one-step procedure. The developed method using ICP-MS for the measurement of ²³¹Pa is more precise than alpha spectrometry and is applicable for freshly produced low-enriched uranium materials. The measured ages are in good agreement with the reported production dates, thus the ²³¹Pa/²³⁵U chronometer can be applied for validation of ²³⁰Th/²³⁴U in nuclear forensics and safeguards.     

Determination of <Superscript>238</Superscript>Pu in plutonium bearing fuels by thermal ionization mass spectrometry

Determination of ²³⁸Pu in plutonium bearing fuels is required as a part of the chemical quality assurance of nuclear fuels. In addition, the determination of ²³⁸Pu is required in nuclear technology for many other applications, e.g., for developing isotope correlations and while using ²³⁸Pu as a spike (tracer) in isotope dilution α-spectrometry (IDAS). This determination usually involves the use of α-spectrometry on purified Pu sample. In view of the random errors associated with the counting statistics and the systematic errors due to (1) in-growth of ²⁴¹Am in purified Pu sample and (2) tail contribution correction methodology in α-spectrometry, the precision and accuracy obtainable by α-spectrometry are limited. Thermal ionization mass spectrometry (TIMS) is generally used for the determination of different Pu isotopes other than ²³⁸Pu. This is due to the ubiquitous isobaric interference from ²³⁸U at ²³⁸Pu in TIMS. Recently, we have carried out studies on the formation of atomic and oxide ions of U and Pu by TIMS and developed a novel approach using interfering element correction methodology to account for the isobaric interference of ²³⁸U at ²³⁸Pu in TIMS. This methodology is based on the addition of ²³⁵U (enrichment >90 atom%) to Pu sample followed by the determination of ²³⁸U/²³⁵U atom ratio using UO⁺ ion and determination of Pu isotope ratios using Pu⁺ ion, from the same filament loading. The TIMS methodology was used for the determination of ²³⁸Pu in different Pu samples in U based nuclear fuels from PHWRs with ²³⁸Pu content about 0.2 atom%. The ²³⁸Pu determination was also carried out using α-spectrometry. This paper reports the results obtained by the two methods and presents the ments and shortcomings of the two approaches.     

Determination of234U/238U activity ratios in Syrian phosphates

The concentrations of uranium and the²³⁴U/²³⁸U ratio in natural Syrian phosphates were measured by gamma- and alpha-ray spectroscopy. The²³⁴U/²³⁸U activity ratios showed that uranium in Syrian phosphate is in equilibrium under the climatic conditions. Soma anomalous observations in these ratios were explained by earlier leaching of the phosphate by water (rain or other).     

Anomalously high 234U/238U activity ratios of Tatsunokuchi hot spring waters, Ishikawa Prefecture, Japan

Uranium concentration and the ²³⁴U/²³⁸U activity ratio have been measured for the Tatsunokuchi hot spring waters of Ishikawa Prefecture in Japan, collected periodically over a long period (1977-2000). The concentration of ²³⁸U varied drastically between 0.045 and 1.02 mBq/l (a factor of about 20), while the ²³⁴U concentration was almost unchanged, ranging from 2.30 to 3.07 mBq/l. Resultant ²³⁴U/²³⁸U activity ratios showed a wide range from 2.7 to 51. Equilibrium calculation by using the geochemical code showed that U for one end-member representing low uranium contents and very high ²³⁴U/²³⁸U ratios was expected to exist as UO₂(CO₃)₂ ^2-. By using the U isotopic and ¹⁴C dating methods, the age of this water was roughly estimated to be in the range of 10⁴-10⁵ years.     

Determination of 234U/238U isotope ratios in environmental waters by quadrupole ICP-MS after U stripping from alpha-spectrometry counting sources

The ²³⁴U/²³⁸U isotope ratio has been widely used as a tracer for geochemical processes in underground aquifers. Quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS) equipped with a high-efficiency nebulizer and a membrane desolvator was employed for the determination of ²³⁴U/²³⁸U isotope ratios in natural water samples. The instrumental limit of detection for ²³⁴U was at the low pg L⁻¹ level with very low sample consumption. Measurement precision (²³⁴U/²³⁸U) was 3–5% for bottled mineral water with elevated uranium concentration (>1 μg L⁻¹). For the analysis of groundwater samples from the Almonte-Marisma underground aquifer (Huelva, Spain), uranium was stripped from stainless steel planchets that had previously been used as radiometric counting sources for alpha-particle spectrometry. Potential spectral interferences from other metals introduced during the dissolution were investigated. Matrix-matched blank solutions were needed to subtract the background on ²³⁴U due to the formation of platinum argides, and to allow for mass bias correction and background correction. The Pt appears to be an impurity present in the stainless steel, either as a minor component by itself or after extraction from the anode and a subsequent uranium electrodeposition. The ²³⁴U/²³⁸U isotope ratio data were in very good agreement with those of alpha spectrometry, while precision was improved by a factor of up to 10 and counting time was reduced down to ~20 min (10 replicate measurements).     

Activity disequilibrium between 234U and 238U isotopes in natural environment

The aim of this work was to calculate the values of the ²³⁴U/²³⁸U activity ratio in natural environment (water, sediments, Baltic organisms and marine birds from various regions of the southern Baltic Sea; river waters (the Vistula and the Oder River); plants and soils collected near phosphogypsum waste heap in Wi?linka (Northern Poland) and deer-like animals from Northern Poland. On the basis of the studies it was found that the most important processes of uranium geochemical migration in the southern Baltic Sea ecosystem are the sedimentation of suspended material and the vertical diffusion from the sediments into the bottom water. Considerable values of the ²³⁴U/²³⁸U are characterized for the Vistula and Oder Rivers and its tributaries. The values of the ²³⁴U/²³⁸U activity ratio in different tissues and organs of the Baltic organisms, sea birds and wild deer are varied. Such a large variation value of obtained activity ratios indicates different behavior of uranium isotopes in the tissues and organisms of sea birds and wild animals. This value shows that uranium isotopes can be disposed at a slower or faster rate. The values of the ²³⁴U/²³⁸U activity ratio in the analyzed plants, soils and mosses collected in the vicinity of phosphogypsum dumps in Wi?linka are close to one and indicate the phosphogypsum origin of the analyzed nuclides. Uranium isotopes ²³⁴U and ²³⁸U are not present in radioactive equilibrium in the aquatic environment, which indicates that their activities are not equal. The inverse relationship is observed in the terrestrial environment, where the value of the of the ²³⁴U/²³⁸U activity ratio really oscillates around unity.     

Determination of U/U atom ratio in uranium samples using liquid scintillation counting (LSC)

A correlation has been developed for the determination of ²³⁵U/²³⁸U atom ratio in uranium samples using liquid scintillation counting (LSC). The ²³⁵U/²³⁸U atom ratio determined by thermal ionization mass spectrometry (TIMS) was correlated to the ratio of (i) α-count rate and (ii) Cerenkov count rate due to ^234mPa in the sample; both measured by LSC. This correlation is linear over the range of ²³⁵U/²³⁸U atom ratio encountered in the nuclear fuel samples, i.e. the low enriched uranium (LEU) samples with ²³⁵U < 20 atom%. The methodology based on this correlation will be useful for the quick determination and verification of ²³⁵U/²³⁸U atom ratios in fuel samples using cost effective technique of LSC.     

Distribution of uranium,plutonium, and <Superscript>241</Superscript>Am in soil samples from Idaho National Laboratory

Soil materials used were collected in the early 1970s at Idaho National Laboratory near the Subsurface Disposal Area (SDA). Samples from a depth of 0–4 and 4–8 cm at two different sites located on the northeast corner of the SDA perimeter were analyzed. The concentration of ²³⁴U, ²³⁵U, ²³⁶U, and ²³⁸U in soil digests were measured by mass spectrometry. Uranium isotopic composition of the soil at the two sample sites and depths is compared to previously measured concentrations of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, and ²⁴¹Am. Implications for remediation of contaminated soils surrounding the SDA are discussed.     

The concentration of <Superscript>238</Superscript>U and the levels of gross radioactivity in surface waters of the Van Lake (Turkey)

Gross α and gross β activities and ²³⁸U concentrations were determined in 18 surface water samples collected from Van Lake. The instrumentations used to count the gross α and gross β activities and to determine the ²³⁸U concentrations were α/β counter of the multi-detector low background system (PIC-MPC-9604) and Inductively Coupled Plasma-Mass Spectrometry (Thermo Scientific Element 2), respectively. Concentrations ranging from 0.001 to 0.021 Bq L⁻¹ and from 0.111 to 2.794 Bq L⁻¹ were observed for the gross α and β activities in surface waters, respectively. For all samples the gross β activities were higher than the corresponding gross α activities. The results indicated that the gross α radioactive contamination in water samples was lower than recommended values for the guideline of drinking waters and most of the gross β activities in water samples were higher than those in the same procedure. The ²³⁸U concentrations ranged from 74.49 to 113.2 μg L⁻¹ in surface waters. The obtained results have showed that ²³⁸U concentrations are higher than guideline values for uranium.     

A comparative study of234U/238U alpha-activity ratios determined by alpha-spectrometry and calculated from mass spectrometric data

²³⁴U/²³⁸U α-activity ratios determined by α-spectrometry (AS) and those calculated from the atom ratio data using the half-life values are compared in some of the isotopic reference materials of uranium and a few other uranium samples. For α-spectrometry, electrodeposited sources were prepared and a large area passivated ion implanted (IPE) detector (450 mm²) was used for recording the α-spectra. The isotopic composition of U was determined by thermal ionisation mass spectrometry (TIMS) and the recommended half-life values of²³⁴U and²³⁸U were used to calculate the α-activity ratio. It is observed that²³⁴U/²³⁸U α-activity ratios calculated from the atom ratio data are consistently high, with a mean difference of about 5%, when compared to the α-spectrometry results. This discrepancy warrants confirmation by a few more laboratories and suggests redetermination of the half-life values of²³⁴U and²³⁸U.     

Radioactivity levels of <Superscript>238</Superscript>U and <Superscript>232</Superscript>Th,the α and β activities and associated dose rates from surface soil in Ulu Tiram,Malaysia

A survey was carried out to determine terrestrial gammaradiation dose rates, the concentration level of ²³⁸U and ²³²Th and α and β activities for the surface soil in Ulu Tiram, Malaysia A 125 measurements were performed using a NaI(T1) gamma-ray detector with crystal size of 1″ × 1″ on 15 soil samples collected from the site area about 102 km^{2 238}U and ²³²Th concentrations were determined in soils by using hyper pure germanium (HPGe) gamma-ray spectrometry. The activity of α and β from the surface soil was counted by using alpha beta counting system. The average value of ²³⁸U and ²³²Th concentrations in soil samples collected are 3.63±0.39 ppm within the range of 1.74±0.20 to 4.58±0.48 and 43.00±2.31 ppm within the range of 10.68±0.76 to 82 10±4.01 ppm, respectively. The average estimate of α and β activity in soil samples collected are 0.65±0.09 Bqg⁻¹ and 0.68±0.08 Bqg⁻¹, respectively. The average of terrestrial gamma-radiation dose rates measured in Ulu Tiram was found to be 200 nGy h⁻¹, within the range of 96 to 409 nGy h⁻¹. The population weighted outdoor annual effective dose was 1.2 mSv.     

Studies on the geochemical behaviour of uranium isotopes in coastal environment of the east coast of india

Samples of coastal marine sediments of the East Coast of India were leached with a saturated solution of ammonium carbonate for the extraction of uranium from the sediment particle surface without attacking the mineral core of the particles. All the sediment samples were found to exhibit a²³⁴U/²³⁸U activity ratio in the range of 1.07 to 1.14. On removal of surface organic matter, the²³⁴U/²³⁸U activity ratio is close to 1.00, indicating that the anomaly between²³⁸U and²³⁴U exists only on the labile surface layer. However, no such variations are observed in²³⁵U/²³⁸U activity ratios. These ratios are close to 0.045 which is the same as that of natural uranium.