Measurement Of 129I Research Articles

Tracing Ocean Circulation and Mixing From the Arctic to the Subpolar North Atlantic Using the 129I–236U Dual Tracer

AbstractThis study represents the first use of the artificial radionuclides 129I and 236U, released into the ocean mainly from Nuclear Reprocessing Plants, as a dual tracer in the vicinity of Iceland with novel estimation of ocean circulatory pathways and mixing in the region. Iceland lies at the gateway to the Arctic where warm, saline Atlantic waters interact with waters of Arctic origin in ways that have critical consequences for the strength and stability of the Atlantic Meridional Overturning Circulation. Many of these interactions are not yet fully understood, such as how Atlantic water circulates around the Arctic Ocean and Nordic Seas and the composition and fate of the major overflows of the Greenland‐Scotland Ridge. Using new and previous measurements of 129I and 236U in seawater, we present a new method of appraising water mass provenance and mixing in the form of the 129I–236U dual mixing plot. With this method, we estimate that at least half the Atlantic‐origin water entering the Arctic Ocean circulates around the Canada Basin before exiting at Fram Strait and that this outflow is increased by about 40% by mixing with Return Atlantic Water “short‐circuiting” the Arctic Ocean at Fram Strait. We present tracer‐based evidence that water carried by the East Greenland Current has an unbroken pathway to the Faroe‐Shetland Channel and that Iceland‐Scotland Overflow Water (ISOW) entrains 60% Labrador Sea Water during transit past southeast Iceland. We present an unambiguous way to differentiate ISOW from DSOW after they partially merge in the Irminger Sea.

Measurements of 129I in waters of China, India and Arabian Sea

AMS experiments were conducted to use 129I as a tracer of the outspread of nuclear pollution from the 2011 Fukushima Nuclear Accident over India, China and the Arabian Sea. Water samples were collected repetitively between 2016 and 2020. Seawater samples from Shanghai and from Disneyland Hong Kong had low iodine concentrations of 1.4 × 107 atoms/L. However, the India big rivers and the Arabian Sea, have about one order of magnitude higher iodine concentrations on average 2.3 × 108 atoms/L. The values of the 129I tracer concentrations decrease towards south-west direction in the Arabian Sea and is reduced for rivers in the Himalayan region close to Tibet. At Muscat and Salalah, located on the Oman coast, the measured concentration in water samples were on average 2.2 × 107 atoms/L. The enhanced concentation of the 129I tracer in India is likely produced by internal pollution sources.

Backgrounds and blanks in Iodine-129 measurements at the Australian National University

The molecular hydride negative ions of mass 129 amu, 127IH2−, 127ID− and 128TeH−, have been studied in order better to understand potential backgrounds in AMS measurements of 129I. All three of these ions appear to be stable or, if metastable, to have lifetimes that are sufficiently long to allow at least some of them to reach the high voltage terminal of the accelerator. It is found, however, that these make only a minor contribution to the combined rate of 127I7+ and 128Te7+ ions that pass around the analysing magnet when it is set for 129I7+ detection. The principal contribution comes instead from the injection of 127I− ions into the accelerator along with the 129I− ions, despite the use of a low Cs sputtering energy in the ion source that was intended to eliminate them. This contribution is, however, small and is effectively removed by a Wien filter. In addition, a sample of Woodward iodine, obtained from the University of Arizona, was found to have an 129I/127I ratio of (13.3 ± 0.9) × 10−15. This is the lowest ratio so far reported. In contrast, the batch of Woodward iodine that was being used as an iodine carrier in our laboratory was found to have a much higher ratio of (78.2 ± 2.4) × 10−15. A search for a lower ratio blank failed to find a suitable material.

The performance of a home-made 300 kV AMS system at CIAE

In order to develop a AMS system for heavy isotopes measurement at China Institute of Atomic Energy (CIAE), a home-made 300 kV AMS system has been established. The measurement methods for 129I and 239Pu have been developed with the system. The transmission efficiency of 65 % for 129I and 25 % for Uranium have been obtained with this system. The 129I measurements with uncertainty of 2.5 % and sensitivity of 129I/127I = 2 × 10−14 are achieved. The uncertainty of 5 % and detection limitation of 0.5 fg are obtained for 239Pu measurements.

R-Process Radioisotopes from Near-Earth Supernovae and Kilonovae

Abstract The astrophysical sites where r-process elements are synthesized remain mysterious: it is clear that neutron star mergers (kilonovae (KNe)) contribute, and some classes of core-collapse supernovae (SNe) are also possible sources of at least the lighter r-process species. The discovery of 60Fe on the Earth and Moon implies that one or more astrophysical explosions have occurred near the Earth within the last few million years, probably SNe. Intriguingly, 244Pu has now been detected, mostly overlapping with 60Fe pulses. However, the 244Pu flux may extend to before 12 Myr ago, pointing to a different origin. Motivated by these observations and difficulties for r-process nucleosynthesis in SN models, we propose that ejecta from a KN enriched the giant molecular cloud that gave rise to the Local Bubble, where the Sun resides. Accelerator mass spectrometry (AMS) measurements of 244Pu and searches for other live isotopes could probe the origins of the r-process and the history of the solar neighborhood, including triggers for mass extinctions, e.g., that at the end of the Devonian epoch, motivating the calculations of the abundances of live r-process radioisotopes produced in SNe and KNe that we present here. Given the presence of 244Pu, other r-process species such as 93Zr, 107Pd, 129I, 135Cs, 182Hf, 236U, 237Np, and 247Cm should be present. Their abundances and well-resolved time histories could distinguish between the SN and KN scenarios, and we discuss prospects for their detection in deep-ocean deposits and the lunar regolith. We show that AMS 129I measurements in Fe–Mn crusts already constrain a possible nearby KN scenario.

Low-energy 14C and multi-element HVE AMS systems

Two sub-MV accelerator mass spectrometers based on vacuum-insulated accelerators were designed, built, and tested by High Voltage Engineering Europa B.V. The first one is dedicated to 14C measurements. Both low- and high-energy mass analysis is done with permanent magnets. Unique to the 14C AMS system is that the accelerator terminal is equipped with a charge state selector suppressing ions of unwanted charge states, thereby reducing the system background for the 14C/12C ratio to the low 10−15 level. The 14C/12C precision is measured to be 0.16%. The second AMS system is a multi-element for 10Be, 14C, 26Al, and 129I measurements. The analysis of actinides is supported as well. It is equipped with two analyzing magnets in the high-energy spectrometer. The measured machine background for carbon is 7 × 10−16, for beryllium 5 × 10−15, for aluminum < 5 × 10−15 and for iodine 4 × 10−14.

Measurements of 129I in the Pacific Ocean at Scripps Pier and Pacific Northwest sites: A search for effects from the 2011 Fukushima Daiichi Nuclear Power Plant accident and Hanford

Radionuclides from the Fukushima Daiichi Nuclear Power Plant were released directly into the ocean as a result of the Great East Japan Earthquake on March 11, 2011. This material became entrained in surface ocean currents and subsequently transported for great distances. In June 2011, a few months after the disaster, we began a surface ocean 129I monitoring program, with samples from Scripps Pier, La Jolla, California, USA, with the expectation that surface currents originating off the east coast of Japan would eventually carry radionuclides to the La Jolla site. After 7 years of ocean transport, a distinct signal has not yet arrived at Scripps Pier. We have however, recorded an interesting systematic seasonal 129I time series record that stems from surface circulation variations along the California coast. To provide a more comprehensive picture of the 129I budget in coastal surface waters off the west coast of the U.S., we also include 129I data from the Columbia River, and offshore sites along the coast of Washington State. Anthropogenic nuclides are carried by the Columbia River into the Pacific Ocean from the vicinity of the decommissioned Hanford nuclear facility. We find highly elevated 129I/127I values in the Columbia River, downstream from the Hanford site, but this anthropogenic 129I becomes significantly diluted once it reaches the Pacific Ocean. Nonetheless, its imprint persists in surface seawater off the west coast of the U.S. that has significantly higher 129I/127I levels than other surface sites in the Pacific Ocean.

Actual 129I concentration levels in the Lower Danube River and in the Black Sea

Currently, several locations of the North Atlantic Ocean have the 129I concentration levels 104–105 times higher than those of the pre-nuclear era. As a consequence, the southeastern part of Europe, with its rivers and seawaters, should be influenced by the outspread through the atmospheric and hydrospheric transport of iodine-129. This is a long lived fission isotope and a “low beta emitter”. It can be used as long-term tracer for nuclear pollution if the concentration of 129I is known in the investigated geographical region. This AMS study has determined the 129I concentrations in the southeast part of Europe, from the Lower Danube River, the Danube Delta and the Black Sea. The 129I concentrations measured in the Black Sea were in the range of (1–1.4) × 108 atoms/L, which equals the range values of the North Atlantic Ocean at latitudes (31°–50°N) of (0.4–1.3) × 108 atoms/L. For the Danube Delta, the measured concentration values were very close to those of the Black Sea, due to the small inflow from the sea. For the region of the Lower Danube, 129I concentrations were (4.1–7.4) × 107 atoms/L. The averaged results of 129I measurements provided the actual baseline of (1.2 ± 0.1) × 108 atoms/L valid for the Danube Delta and the Black Sea region and of (6.4 ± 0.1) × 107 atoms/L for the Lower Danube.

Independent measurements of 129I content in environmental reference materials using accelerator and thermal ionization mass spectrometry

Iodine environmental measurement programs are in need of new materials with certified 129I activity. Frequently 129I measurements are validated in the literature using the standard material IAEA-375, Chernobyl soil, which is the only soil/sediment material with a recommended 129I activity. IAEA-375 has not been available for purchase since 2010. This study is an extension of previous work at INL to include four additional standard materials that are commercially available (NIST materials: RM 8704, Buffalo River sediment, SRM 2710a, Montana I soil, and IAEA materials: SL-1, lake sediment, IAEA-385, Irish Sea sediment). These materials have certified or recommended activities for a variety of radionuclides but not for 129I. This paper reports a comparison of accelerator mass spectrometry (AMS) and thermal ionization mass spectrometry (TIMS) data for 129I activity, as well as the 129/127I ratios for these standards to assist in identifying a suitable alternative for IAEA-375. Two independent chemical separation and mass spectrometric analysis techniques have been applied in an effort to corroborate the data. Both methods were validated via analyses of IAEA-375 for 129I and show good agreement with the recommended activity of 1.7 × 10−3 Bq kg−1 for 129I; (1.6 × 10−3 Bq kg−1 by AMS and 1.8 × 10−3 Bq kg−1 by TIMS) with both sets of results within the 95% confidence interval of the recommended value.

Historical record of nuclear activities from 129I in corals from the northern hemisphere (Philippines)

Iodine-129 is a long-lived fission product that is majorly released in human nuclear activities (HNA) such as nuclear bomb testing, nuclear fuel reprocessing, and nuclear accidents. It is a good environmental tracer and former measurements of 129I in corals from the southern hemisphere show the increasing trend of 129I concentrations in the marine environment caused by HNA. Here we show time series of 129I/127(stable)I isotopic ratios in two coral cores from the northern hemisphere (Philippines) and how these record 129I released from HNA in even greater, unprecedented detail. Corals were taken from the Pacific Ocean (Baler) and South China Sea (Parola) sides of the Philippines. We observed nearly identical peaks (129I/127I ∼ 31.5 × 10−12) in both the Baler and Parola records, each attributed to the year 1962 – the year with the highest recorded amount of 129I release from nuclear bomb testing. This 1962 129I bomb signal offers a new time marker that can be used to establish or confirm age models of corals, comparable to or possibly better than the well-known coral 14C bomb peak. We also observed nuclear fuel reprocessing and Chernobyl accident 129I signals in years 1977, 1980, and 1986, concurrently in Parola and with 9 to 11-year lags in Baler. This discrepancy in timing suggests that 129I was transported to the South China Sea and Pacific Ocean sides of the Philippines directly from the atmosphere and through prevailing ocean currents, respectively. Lastly, we observed surprisingly high 129I/127I isotopic ratios (i.e., 22.8 to 38.9 × 10−12) in the Parola record after the year 1996, which is in contrast to the decreasing trend observed in the Baler record and in published 129I releases of different HNA. These results possibly indicate the presence of unknown sources of 129I in the South China Sea region.

Preliminary Investigation on the Rapid and Direct AMS Measurement of 129I in Environmental Samples without Chemical Separation

AbstractAccelerator mass spectrometry (AMS) is the most sensitive method for measuring 129I in environmental samples available today, with a detection limit of about 10–15 for 129I/127I. A drawback of the technique is the time-consuming chemical separation required to prepare AMS targets from raw samples. This step significantly limits applications requiring rapid analyses and large numbers of samples, for example, in monitoring studies associated with nuclear accidents. This work introduces a direct method for 129I measurements by AMS that does not require chemical separation. In this approach, stable iodine (127I) is added to a matrix of niobium (Nb) powder and mixed with dried raw sample. This mixture is pressed directly into a sputter target for AMS analysis. Two types of environmental samples have been tested in this work, seaweed and sediment. No anomalous behavior was noted in the Cs+ sputtering behavior of the targets prepared from these materials. The 129I/127I ratios and 129I concentrations measured by this rapid method were found to be in agreement with reported values that used a conventional AMS method for the same material. Based on our findings, we expect that such rapid measurements can be applied to a wide variety of materials, in addition to seaweed and sediment, as long as the sputtering-induced adverse effects do not prevent the stable operation of the ion source. The method is especially useful for screening large numbers of samples before more precise analyses are made.

Measurement of 129I in ferromanganese crust with AMS

In the present study, the analytical method for 129iodine (129I) in ferromanganese crusts is developed and 129iodine/127iodine (129I/127I) ratio in ferromanganese crusts is measured by the accelerator mass spectrometry (AMS). The developed method is applied to analyze 129I/127I ratio in two ferromanganese crusts MP5D44 and CXD08-1 collected from the Mid-Pacific Ocean. The results show that 129I/127I ratio in MP5D44 and CXD08-1 crusts varies from 7×10–14 to 1.27×10–12, with the lowest value falling on the detection limit level of AMS reported by previous literatures. For the depth distribution of 129I/127I, it is found that both MP5D44 and CXD08-1 crusts have two growth generations, and the 129I/127I profiles in two generations all displayed an approximate exponential decay. According to the 129I/127I ratio, the generate age of bottom layer of MP5D44 and CXD08-1 was estimated to be 54.77 and 69.69 Ma, respectively.

The measurement of 129I in ferromanganese crusts and aerosol samples with AMS at CIAE

The determination of long-lived nuclide 129I in terrestrial formations has many important applications. The AMS measurement method of 129I has been set up for many years at China Institute of Atomic Energy (CIAE). For further exploring the potential applications of 129I, samples of Deep Sea Ferromanganese Crusts (DSFC) and aerosol were analyzed by Accelerator Mass Spectrometry (AMS). The results show that 129I is not only a good tool for dating, but also an ideal nuclide for nuclear safety monitoring. The newest experimental progress and the main results are detailed in this presentation.

New insights on the role of sea ice in intercepting atmospheric pollutants using 129I

Measurements of 129I carried out on sea ice samples collected in the central Arctic Ocean in 2007 revealed relatively high levels in the range of 100–1400×107 at L−1 that are comparable to levels measured in the surface mixed layer of the ocean at the same time. The 129I/127I ratio in sea ice is much greater than that in the underlying water, indicating that the 129I inventory in sea ice cannot be supported by direct uptake from seawater or by iodine volatilization from proximal (nearby) oceanic regimes. Instead, it is proposed that most of the 129I inventory in the sea ice is derived from direct atmospheric transport from European nuclear fuel reprocessing plants at Sellafield and Cap La Hague. This hypothesis is supported by back trajectory simulations indicating that volume elements of air originating in the Sellafield/La Hague regions would have been present at arctic sampling stations coincident with sampling collection.

Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site

A primary obstacle in understanding the fate and transport of the toxic radionuclide 129I (a thyroid seeker) is an accurate method to distinguish it from the stable isotope, 127I, and to quantify the various species at environmentally relevant concentrations (~10−8M). A pH-dependent solvent extraction and combustion method was paired with accelerator mass spectrometry (AMS) to measure ambient levels of 129I/127I isotope ratios and iodine speciation (iodide (I−), iodate (IO3−), and organo-I (OI)) in aquatic systems. The method exhibited an overall uncertainty of 10% or less for I− and IO3−, and less than 30% for OI species concentrations and enabled 129I measurements as low as 0.001Bq/L (1Bq/L=10−13M). The method was used to analyze groundwater from the Savannah River Site (SRS), South Carolina, USA, along a pH, redox potential (Eh), and organic carbon gradient (8–60μM DOC). The data confirmed that the 129I/127I ratios and species distribution were strongly pH dependent and varied in a systematic manner from the strongly acidic source. While 129I speciation in plume samples containing total I concentrations >1.7Bq/L was similar whether measured by AMS or GC–MS ([I−]≫[IO3−]=[OI]), AMS enabled 129I speciation measurements at much lower concentrations than what was possible with GC–MS. AMS analyses demonstrated that groundwater samples minimally impacted by the plume were still orders of magnitude higher than ambient 129I concentrations typically found elsewhere in the USA groundwaters and rivers. This is likely due to past atmospheric releases of volatile 129I species by SRS nuclear reprocessing facilities near the study site. Furthermore, the results confirmed the existence of 129I not only as I−, but also as OI and IO3− species.

Input of 129I into the western Pacific Ocean resulting from the Fukushima nuclear event

We present an initial characterization of the input of 129I into the Pacific Ocean resulting from the 2011 Fukushima nuclear accident. This characterization is based primarily on 129I measurements on samples collected from a research cruise conducted in waters off the eastern coast of Japan in June 2011. These measurements were compared with samples intended to reflect pre-Fukushima background that were collected during a May 2011 transect of the Pacific by a commercial container vessel. In surface waters, we observed peak 129I concentrations of ~300 μBq/m3 which represents an elevation of nearly three orders of magnitude compared to pre-Fukushima backgrounds. We coupled our 129I results with 137Cs measurements from the same cruise and derived an average 129I/137Cs activity ratio of 0.442 × 10−6 for the effluent from Fukushima. Finally, we present 129I depth profiles from five stations from this cruise which form the basis for future studies of ocean transport and mixing process as well as estimations of the total budget of 129I released into the Pacific.

Speciation Analysis of 129I in Seawater by Carrier-Free AgI–AgCl Coprecipitation and Accelerator Mass Spectrometric Measurement

A rapid and simple method was developed for speciation analysis of (129)I in seawater by selective coprecipitation of carrier-free iodide and accelerator mass spectrometry (AMS) measurement of (129)I. Iodide was separated from seawater and other species of iodine by coprecipitation of AgI with Ag2SO3, AgCl, and AgBr by addition of only 100 mg/L Ag(+) and 0.3 mmol/L NaHSO3 at pH 4.2-5.5. The separation efficiency of iodide was more than 95%, and crossover between (129)IO3(-) and (129)I(-) fractions is less than 3%. Iodate and total inorganic iodine were converted to iodide by use of NaHSO3 at pH 1-2 and then separated by the same method as for iodide. Ag2SO3 in the coprecipitate was removed by washing with 3 mol/L HNO3 and the excess AgCl and AgBr was removed by use of diluted NH3, and finally a 1-3 mg precipitate was obtained for AMS measurement of (129)I. The recovery of iodine species in the entire procedure is higher than 70%. Six seawater samples collected from the Norwegian Sea were analyzed by this method as well as a conventional anion-exchange chromatographic method; the results from the two methods show no significant difference (p = 0.05). Because only one separation step and fewer chemicals are involved in the procedure, this method is suitable for operation on board sampling vessels, as it avoids the transport of samples to the laboratory and storage for a longer time before analysis, therefore significantly improving the analytical capacity and reliability of speciation analysis of (129)I. This improvement can stimulate oceanographic tracer studies of (129)I.

Measurement of 129I in an Inorganic Adsorbent

Measurement of 129I in an Inorganic Adsorbent

Release of iodine from organic matter in natural water by K2S2O8oxidation for129I determination

Accelerator mass spectrometry is the only method for measuring 129I in low level environmental samples. In this method, it is essential to convert organic associated iodine into inorganic form for the determination of total 129I or organic 129I because AgI is usually adopted as a target for AMS measurement of 129I. The chemical oxidative method to release iodine from organic matter in natural water was investigated using anion exchange chromatography and CHCl3 extraction methods. K2S2O8 was confirmed to be an ideal oxidative reagent for decomposing organic matters and converting organic iodine to inorganic form. More than 95% of iodine in natural water can be separated by solvent extraction after oxidation under optimal conditions, and the isotopic exchange of iodine in inorganic and organic forms was well completed during the oxidation, being able to result in an identical 129I/127I ratio as in the original water. Our works indicate that the reported chemical oxidation method is a suitable approach for releasing organic associated iodine in natural water to allow separation of iodine and preparation of the AgI target for AMS measurement.

Effect of 3H and 14C Interference on the Radioactivity Measurement of 129I in Low and Intermediate-Level Radwastes

Effect of 3H and 14C Interference on the Radioactivity Measurement of 129I in Low and Intermediate-Level Radwastes