Measurement Of 129I Research Articles

Speciation and migration of 129I in soil profiles

A method has been developed for speciation analysis of ultra low level 129I in soil using sequential extraction combined with coprecipitation for separation of carrier free iodine and AMS measurement of 129I. Two loess profiles collected from northwest China were analyzed for species of 129I and 127I. Similar partitioning of 129I and 127I was observed in the loess profiles, the distribution of iodine isotopes followed an order of organic > leachable > reducible > residue. The 129I concentrations and 129I/127I ratios decreased exponentially with the depth, and 2 orders of magnitude lower in the deepest layer (60 and 90 cm) compared with the top layer, indicating a significant contribution of anthropogenic input in the upper layer, and high retention of 129I in soil. The mobility of 129I in different fractions decreased in an order of leachable > organic > oxides > residue. The results suggest that migration of iodine downwards in the soil profile is a slow process; the oxides and residue are the less mobile fractions of iodine.

AMS measurements of 129I in seawater around Iceland and the Irminger Sea

Large amounts of iodine-129 were, and still are, released into the environment from nuclear facilities, in particular from two reprocessing facilities located on the east coast of the North Atlantic Ocean (Sellafield and La Hague). The main transport path of the releases from the two facilities is through the North Atlantic Current (NAC) and subsequently the Norwegian Coastal Current (NCC) to the Arctic Ocean. Iceland lies on the Scotland–Greenland ridge, which separates the Atlantic and Arctic oceans. 129I data available in that area are scarce despite their importance in modeling 129I dispersion through the North Atlantic and Arctic Oceans. For this reason, we have determined the 129I/127I ratio in seawater samples by means of Accelerator Mass Spectrometry (AMS) from three locations at the Iceland and Irminger Basins at different depths (from surface to 1000m) in order to study the transport pathways of the anthropogenic releases to the waters. The measured 129I/127I ratios, compared to the pre-anthropogenic 129I/127I value, show the strong influence of the artificial 129I discharges in the North Atlantic waters.

Recent changes in Arctic Ocean circulation revealed by iodine‐129 observations and modeling

Anthropogenic radionuclides released into European coastal waters from nuclear fuel reprocessing plants at Sellafield (UK) and La Hague (France) flow northward through the Nordic Seas and label Atlantic Water (AW) entering the Arctic Ocean. Transport of the soluble radionuclide 129I through the Arctic Ocean has been simulated using a numerical model for the period from 1970 to 2010. The simulated tracer distributions closely conform to 129I measurements made across the Arctic Ocean during the mid‐1990s and 2000s and clearly illustrate the dramatic changes in oceanic circulation which occurred during this time. The largest changes in surface circulation were associated with the transition from a negative to a positive phase of the Arctic Oscillation in the early 1990s and the subsequent return to a weak positive phase in the late 1990s and early 2000s. Model and experimental results indicate that a new circulation regime evolved after 2004 when a period of intense, anti‐cyclonic surface stress led to a strengthening of the Beaufort Gyre. We submit that this resulted in a suppression of the cyclonic boundary current of mid‐depth Atlantic Water (AW) below the Beaufort Gyre, with upper AW in the Canada Basin showing signs of a reversal from cyclonic to anti‐cyclonic flow. These results are consistent with the development of a new AW circulation scheme involving a separation between flow at intermediate depths in the Eurasian and Canada Basins which could eventually result in modification of the Arctic intermediate water which feeds the overflows.

Separation and measurement of 129I and 127I in pre-nuclear-era marine algae with ultra-low 129I/127I isotopic ratios

The iodine isotopes 127I and 129I were isolated from marine algal samples to obtain 129I/127I ratios by accelerator mass spectrometry (AMS). The collection efficiency of iodine was 16–99%, and the treatment temperature in the present study was lower than that used in conventional methods for 129I analysis. Using the separation method reported here, we can easily measure ultra-low 129I/127I ratios in the orders of magnitude of 10−13–10−12, which were observed in algal samples from the pre-nuclear era (before 1945). The 129I/127I ratios observed in algae collected from 1929 to 1987 ranged from 10−13 to 10−10. The 129I/127I ratio in algae collected in 1987 was 100–1000times as high as the ratio measured in algae collected before 1945. This dramatic increase in 129I/127I ratio after 1945 is attributed to human activity.

Progress on 129I analysis and its application in environmental and geological researches

Iodine-129 is a naturally generated isotope, but anthropogenic releases are the dominated source of 129I in the present environment. Among many measurement techniques, neutron activation analysis (NAA) and accelerator mass spectrometry (AMS) are only methods used for measurement of 129I in environmental level. Based on its source terms, chemical properties and environmental behaviors, 129I can be applied for geological dating in a range of 2–80Ma, investigation of formation and migration of hydrocarbon, circulation of ocean water, atmospheric process of iodine, as well as reconstruction of dispersion and migration of short-lived radioisotopes of iodine released from nuclear accidents. This article aims to summarize and critically compare the analytical techniques used for 129I measurement and chemical methods for separation of iodine from various sample matrices, purification from the interferences, as well as preparation of suitable target for AMS measurement. The major applications in environmental and geological researches are reviewed, which mainly focus on the new progress and potential development in the future. The application of 129I in the investigation of radioactive contamination from the Fukushima accident is discussed.

Microwave-based digestion method for extraction of 127I and 129I from solid material for measurements by AMS and ICP-MS

This work presents a microwave-based digestion method followed by a radiochemical extraction procedure to extract iodine from environmental matrices that provides iodine in a form suitable for the measurement of 129I by AMS, with shorter preparation times, small sample sizes and higher automation than previous methods. Samples were digested by a microwave digestion method in closed vessels using HNO 3 as oxidizing agent. Following chemical iodine extraction consisted in an organic compound extraction followed by an aqueous solution extraction and iodine precipitation. Prepared samples were used to measure 127I by ICP-MS and 129I by AMS. The method was validated by ICP-MS measuring 127I content in standard reference materials covering a wide variety of biological, soil and sediment matrices: 1547 Peach Leaves, 1537a Tomato Leaves, 1549 Non-Fat Milk Powder, 2704 Buffalo River Sediment, 2711 Montana Soil and 1648 Urban Particulate Matter from the National Institute of Standards and Technology, IAEA-375 Soil and IAEA SL-1 Lake Sediment from the International Atomic Energy Agency and 186 Pig Kidney from Community Bureau of Reference. The recoveries with respect to the reference values were about 90%. Iodine losses during chemical extraction could be due to its volatilization as HI or I2 in acid means. Accurate results for determination in certified materials and good recoveries.

The measurement of 129I for the cement and the paraffin solidified low and intermediate level wastes (LILWs), spent resin or evaporated bottom from the pressurized water reactor (PWR) nuclear power plants

In this paper a relatively simple and low cost analysis procedure to apply to a routine analysis of 129I in low and intermediate level radioactive wastes (LILWs), cement and paraffin solidified evaporated bottom and spent resin, which are produced from nuclear power plants (NPPs), pressurized water reactors (PWR), is presented. The 129I is separated from other nuclides in LILWs using an anion exchange adsorption and solvent extraction by controlling the oxidation and reduction state and is then precipitated as silver iodide for counting the beta activity with a low background gas proportional counter (GPC). The counting efficiency of GPC was varied from 4% to 8% and it was reversely proportional to the weight of AgI by a self absorption of the beta activity. Compared to a higher pH, the chemical recovery of iodide as AgI was lowered at pH 4. It was found that the chemical recovery of iodide for the cement powder showed a lower trend by increasing the cement powder weight, but it was not affected for the paraffin sample. In this experiment, the overall chemical recovery yield of the cement and paraffin solidified LILW samples and the average weight of them were 67±3% and 5.43±0.53g, 70±7% and 10.40±1.60g, respectively. And the minimum detectable activity (MDA) of 129I for the cement and paraffin solidified LILW samples was calculated as 0.070 and 0.036Bq/g, respectively. Among the analyzed cement solidified LILW samples, 129I activity concentration of four samples was slightly higher than the MDA and their ranges were 0.076–0.114Bq/g. Also of the analyzed paraffin solidified LILW samples, five samples contained a little higher 129I activity concentration than the MDA and their ranges were 0.036–0.107Bq/g.

Rapid Detection and Estimation of an Unexpected Atmospheric Release of 129I

A sampling system was designed to rapidly detect an unexpected release of 129I during a weekly batch-sampling of a stack gas. The system consisted mainly of a sampling unit and an iodine monitor with an NaI(T1) scintillation detector. A relationship between in situ count rate of the monitor and 129I activity collected in the sampling unit was derived from several sets of data obtained with the system at the Tokai reprocessing plant. The system and relationship allowed us to estimate the amount of 129I release at an arbitrary time during the batch-sampling. A different iodine monitor with a Ge detector was also tested to overcome a difficulty in selective measurement of 129I with the NaI(T1) scintillation detector in the presence of 85Kr in the target gas. The test demonstrated a feasibility of the real-time, 85Kr-interference-free monitoring of atmospheric 129I release.

129I measurements in lake water for an estimate of regional 129I depositions

Estimates of (129)I depositions from (129)I releases of reprocessing plants are so far based on measurements of soil and rain water samples. Because (129)I concentrations in these samples show a highly temporal and spatial variability, the (129)I deposition values deduced from single measurements cannot be seen as representative for a larger area. Here it is proposed to use lake water as an archive for former (129)I depositions, to overcome these limitations. If the limnological parameters of any lake are known, the local (129)I deposition flux can be deduced which is temporally averaged over the flushing time, and spatially averaged over the catchment area of the lake. Samples were collected from various European lakes and from Lake Baikal (Russia). The (129)I concentration in these samples was measured by means of accelerator mass spectrometry, and values between 0.3 and 8.1x10(8) at/l were obtained. Deduced (129)I deposition fluxes averaged over the flushing times of the lakes range from 0.3 to 9.3x10(12) at/m(2) y. The (129)I deposition fluence measured for Lake Baikal is attributed predominantly to releases from the former Soviet reprocessing facilities Chelyabinsk, Tomsk and Krasnoyarsk, while the (129)I deposition fluxes deduced for all other lakes are attributed to releases from the European reprocessing activities at Sellafield, Marcoule and La Hague.

A routine preparation method for AMS measurement of 129I in solid material

Here we present results of an 129I extraction procedure applied to solid matrices (soils and organic matters), which is based on combustion of samples in an oxygen atmosphere. Stepwise heating and continuous warming of the whole system were critical points in order to achieve relatively satisfactory yields of iodine from samples ranging up to 1.5g. Repeated combustions of blanks show both stable background levels and no significant memory effects. We have processed a series of different types of sample materials including standard soil, maple leaves and surface soil from Uppsala in Central Sweden. The results show analytical reproducibility and agreement with reported values.

129I Variability in precipitation over Europe

We present results and an overview of studies on 129I in precipitation over Europe during the last decade, covering latitudes 37–70°N. The data show about three orders of magnitude variability in concentrations but without specific correlation to latitude when all Europe is considered. The total amount of 129I provided annually by precipitation over Europe composes only a tiny portion of the annual marine discharge but a significant portion of the gaseous discharges from the nuclear reprocessing facilities. Contribution of gaseous releases seems to be significant, although difficult to estimate. As shown by this study, a unified sampling procedure and systematic measurements of 129I in precipitation throughout Europe are needed to achieve a coherent picture about the loading and sources of 129I in precipitation and the atmosphere.

Determination of 129I in environmental samples by AMS and NAA using an anion exchange resin disk

We have developed a new extraction method for the measurement of 129I by accelerator mass spectrometry (AMS) utilizing an anion exchange resin disk. In comparison to traditional methods such as solvent extraction and ion exchange, this method provides for simple and quick sample handling. This extraction method was tested on soil, seaweed and milk samples, but because of disk clogging, the milk samples and some of the seaweed could not be applied successfully. Using this new extraction method to prepare samples for AMS analysis produced isotope ratios of iodine in good agreement with neutron activation analysis (NAA). The disk extraction method which take half an hour is faster than previous techniques, such as solvent extraction or ion exchange which take a few hours. The combination of the disk method and the AMS measurement is a powerful tool for the determination of 129I. Furthermore, these data will be available for the environmental monitoring before and during the operation of a new nuclear fuel reprocessing plant in Japan.

Assessment of 129I measurement at low MV tandem voltages

Significantly higher efficiencies for 129I measurement by Accelerator Mass Spectrometry (AMS) would be possible if 129I3+ ions could be counted at terminal voltages as low as 1MV. However, at M/Q=3, the molecular interference was anticipated to be severe; this has prevented the use of charge 3+ from being adequately considered. Instead, charge 5+ has been used at higher terminal voltages because of the minimal interference. During a recent performance assessment with charge state 3+, a background of 129I/127I≈10−14 was readily obtained and few 86Sr2+ and 43Ca1+ ions were encountered. This surprising result is possibly due to the very low binding energy and consequent poor stability of anions such as CaSr− and Ca3-. Some triply charged molecular ions were found in the energy spectrum at lower stripping gas pressure but their interference with the detection of 129I3+ was readily suppressed with the Ar gas stripper operated at normal thickness. It now appears that as long as the prepared AMS samples are of good chemical purity, the molecular fragments can be expected to remain quite low in intensity and readily resolved by the final detector. As a result, charge state 3+ can be used for 129I measurements at lower terminal voltages with higher overall efficiency.

129I and 119Sn Mössbauer spectroscopy, reversibility window and nanoscale phase separation in binary Ge xSe 1−x glasses

The molecular structure of the prototypical chalcogenide glass system—Ge x Se 1− x in the 0 < x < 1 3 range, has received much scrutiny over the years. These glasses have been probed by modulated DSC, Raman scattering, 119Sn absorption and 129I emission Mössbauer spectroscopy, and neutron scattering. The 129I measurements utilize 129mTe parent as a dopant in glasses, and reveal a bimodal (A, B) distribution of sites, with the site intensity ratio, I B/ I A ( x), tracking changes in glass structure as a function of x. At low x (<0.15) Se n-chains are stochastically cross-linked by Ge additive, and I B/ I A ( x) sharply declines with x. But at x > 0.15 , rigid regions nucleate at the expense of floppy ones, and the ratio I B/ I A ( x) reverses slope to display a global maximum in the 0.20 < x < 0.25 range. The latter coincides with the reversibility window usually taken as signature of self-organization of these networks. At x > 0.26 , these glasses enter a stressed-rigid elastic phase and in the 0.31 < x < 1 3 range nanoscale phase separate into Se-rich and Ge-rich regions. The signature of the latter is saturation of I B/ I A ( x) at a high value of 1.5 at x = 1 3 . 119Sn Mossbauer spectroscopy measurements independently support the picture of broken chemical order of the stoichiometric glass inferred from the 129I Mössbauer experiments. These observations using local probes are well correlated to Raman scattering, modulated differential scanning calorimetric and diffraction measurements.

New measurement of 129I in IAEA-375 reference material

Under an IAEA project for upgrading of reference materials, a new determination of the 129I concentration in the IAEA-375 reference material was performed. A chemical procedure was set up for the preparation of the AgI samples. Measurement of 129I was carried out using the IsoTrace Tandetron AMS facility at University of Toronto. To ensure the accuracy of the calibration, the tuning of the AMS system was iterated using not only the QC (quality control) samples but also all unknown samples. To minimize any possible current-dependent effects between 129I and 127I ions in the injection magnet, low Cs+ sputtering beam intensity (10 μA) was used. The reproducibility in determining the 129I/127I ratio in the IAEA-375 AgI samples was less than 1%. The activity concentration (CA) of 129I in the IAEA-375 reference material was determined to be 1.59±0.08 mBq . kg-1 at 95% confidence level. The present value is about 7% lower than the IAEA recommended value (1.7 mBq . kg-1) listed in 2000 or 20% lower than the recommended value (2 mBq . kg-1) listed in the IAEA AQCS Reference Material Catalogue (2002-2003). Since the IAEA recommended values for IAEA-375 materials was issued about 10 years ago and error range of the recommended values were large, the results we obtained might be useful in upgrading the recommended value.

Iodine 129/CFC 11 transit times for Denmark Strait Overflow Water in the Labrador and Irminger Seas

Iodine 129 discharged from nuclear fuel reprocessing plants in France and the United Kingdom is transported into the Nordic Seas on timescales of 3–5 years. Tracer 129I is subsequently injected into intermediate waters that overflow the sills between Greenland, Iceland, and Scotland and ventilate the North Atlantic Deep Waters (NADW). During the early 1990s, discharges of 129I increased by 600%, resulting in a large, well‐resolved tracer “front” whose passage through the Nordic Seas is presently being observed by a time series of 129I measurements on the WOCE (AR7W) section in the Labrador Sea. The highest 129I levels were measured below depths of 3000 m in Denmark Strait Overflow Water (DSOW). These levels increased by about 300% between 1997 and 2001 to values &gt;40 × 107 atoms/L, indicating that the leading edge of the tracer “front” from the early 1990s was being observed entering the NADW. Using a simple mixing/advection model, 129I and CFC 11 results were used to calculate transit times of 0.4–2.6 years for the flow of DSOW from formation regions in the Nordic Seas to the Labrador Sea. Measurements on samples collected in the Irminger Sea in 2001 gave transit times of 0.3 years for core DSOW immediately south of Denmark Strait and about 2 years for locations off the southern tip of Greenland. An increase in DSOW transit times observed in the Labrador Sea between 1999 and 2001 probably reflects a more general weakening in the subpolar gyre of the North Atlantic during the 1990s.

Reconstruction of 131I radioactive contamination in Ukraine caused by the Chernobyl accident using atmospheric transport modelling

The evaluation of 131I air and ground contamination field formation in the territory of Ukraine was made using the model of atmospheric transport LEDI ( Lagrangian– Eulerian DIffusion model). The 131I atmospheric transport over the territory of Ukraine was simulated during the first 12 days after the accident (from 26 April to 7 May 1986) using real aerological information and rain measurement network data. The airborne 131I concentration and ground deposition fields were calculated as the database for subsequent thyroid dose reconstruction for inhabitants of radioactive contaminated regions. The small-scale deposition field variability is assessed using data of 137Cs detailed measurements in the territory of Ukraine. The obtained results are compared with available data of radioiodine daily deposition measurements made at the network of meteorological stations in Ukraine and data of the assessments of 131I soil contamination obtained from the 129I measurements.

Halogen geochemistry of the McMurdo dry valleys lakes, Antarctica: Clues to the origin of solutes and lake evolution

We have determined the halogen and boron concentrations in the ice-covered lakes of Taylor Valley, Antarctica, to better establish the sources of salts and evolutionary histories of these unusual water bodies. In addition, we report on a series of 129I measurements that were compared with previous 36Cl data that also help constrain the source of solutes and histories of the lakes. The new data, when put into context of previous work on these systems over the past forty years, allow us to make the following conclusions. The primary source of solutes to Lake Hoare, the youngest of the lakes, is the dissolution of marine aerosols and aeolian salts and the chemical weathering of dust on the glaciers. The geochemistry of Lake Fryxell, the brackish water lake, is primarily dominated by the diffusion from a halite-saturated brine at the sediment-water interface and the recent infilling of the lake by glacier meltwater. These waters have chemical weathering and marine aerosols components. Lake Bonney has two distinct lobes whose hypersaline hypolimnia have different chemistries. Both of the lobes are remnants of ancient marine waters that have been modified by the input of weathering products. This lake has also been modified by periods of cryogenic concentration when solutes have been lost via mineral precipitation. Thus the geochemistry of Lake Bonney owes its unusual geochemistry, in part, to variations in the climate in the Taylor Valley over at least the past 300kyr. The 129I data from the Taylor Valley are similar to those from fracture fluids in crystalline rocks from the Northern Hemisphere.

A review of methane and gas hydrates in the dynamic, stratified system of the Blake Ridge region, offshore southeastern North America

The Blake Ridge region lies on the passive margin of southeastern North America and contains a large amount of methane gas hydrate. The methane and methane gas hydrate are predominantly biogenic, apparently produced by CO 2 reduction. Reflection seismics indicate that bottom-simulating reflectors (BSRs) enclose ∼55,000 km 2, with high-amplitude BSRs covering ∼26,000 km 2. Ocean Drilling Program (ODP) Leg 164 drilled three deep holes on a 10-km-long transect (Sites 994, 995, and 997; water depth 2770–2798 m). Based on sampling and geochemical, thermal, seismic, and borehole geophysical measurements, gas hydrates are most likely present between ∼190 and 450 m in sediment column. Gas hydrate is most often disseminated throughout the sediment column, although concentrations occur within specific sedimentary horizons, within supposed fault zones, and at the base of gas hydrate stability (BGHS) where methane recycling produces more pervasive concentrations of gas hydrate. Estimates of gas hydrate inventory are based on a variety of methods including geochemical proxies, vertical seismic profiling, electric logging, and measurements of in situ methane. Over the entire sediment column, at least ∼2–4% of pore space volume (1–2% sediment volume) is occupied by methane gas hydrates, but average and maximum estimates are 5.4% and 12%, respectively. Extrapolation of vertical gas hydrate and methane inventory over the area containing high-amplitude BSRs yields estimates of 67–406 Gt (gigatons, 10 15 g) of methane gas hydrate (or 9–52 Gt of methane) and 2.6–27 Gt of methane occurring as gas bubbles below the BGHS. Average values are 185 Gt of gas hydrate and 24 Gt of methane as gas hydrate. Any gas hydrate occurring outside the area underlain by BSRs (as suggested by geochemical evidence) or that associated with low-amplitude BSRs may increase these estimates by an unknown factor. Various data give conflicting pictures of mass transport with Blake Ridge sediments. The data can be reconciled by viewing the upper sedimentary section (<∼150 m) as dominated by diffusion, and the lower section characterized by buoyant advection (migration) of gaseous methane with both modes of transport overprinting generally low rates of pore-fluid movement (∼20 cm kyear −1). Methane migration seems necessary to produce observed gas hydrate distribution and inventory estimates. Accumulation of gas hydrate in the Blake Ridge sediments depends on the amount of methane leaving the system versus the amount of methane entering the gas hydrate stability zone (GHSZ) over geologic time. Although there are some point sources of methane loss from the sediments (e.g., seafloor seeps, ODP Site 996) of unknown magnitude, most of the documented methane loss occurs through diffusion and consumption at the sulfate–methane interface (SMI) by anaerobic methane oxidation (AMO; ∼2×10 8 mol year −1). Methane entering the GHSZ at a rate of ∼1.3×10 9 mol year −1 indicates a methane-trapping efficiency of ∼85%. 129I measurements suggest that the Blake Ridge system has accumulated gas hydrate over as much as 55 million years.

129I and 129I/127 I ratio determination in environmental biological samples by RNAA, AMS and direct γ -X spectrometry measurements

Different techniques are available for the measurement of 129I or 129I/127 I ratio. Due to the lack of internationalcertified reference material for 129I, intercomparison exerciseson the measurement of 129I are very rare. This study presents twointercomparison exercises between three techniques: direct γ-X spectrometry,radiochemical neutron activation analysis and accelarator mass spectrometry.A reference material was constituted with a Fucus serratus collected on thefrench channel coast. A significative correlation between the results givenby the three techniques was proven on this material and on a set of otherFucus serratus samples presenting different activity levels.