Unique Isotopic Composition Research Articles

Isotopic Composition of C, N, and S as an Indicator of Endometrial Cancer.

The metabolic pathway of cancerous tissue differs from healthy tissue, leading to the unique isotopic composition of stable isotopes at their natural abundance. We have studied if these changes can be developed into diagnostic or prognostic tools in the case of endometrial cancer. Measurements of stable isotope ratios were performed using isotope ratio mass spectrometry for nitrogen, carbon, and sulfur isotopic assessment. Uterine tissue and serum samples were collected from patients and the control group. At a natural abundance, the isotopic compositions of all three of the studied elements of uterus cancerous and healthy tissues are different. However, no correlation of the isotopic composition of the tissues with that of serum was found. Differences in the isotopic composition of the tissues might be a potential prognostic tool. However, the lack of a correlation between the differences in the isotopic composition of the tissues and serum seems to exclude their application as diagnostic biomarkers, which, however, might be possible if a position-specific isotopic analysis is performed.

Constraints on the Nd-isotopic composition and nature of the last major influx of magma into the Bushveld Complex

The Pyroxenite Marker, a thin, orthopyroxene-dominated marker horizon, is observed towards the top of the Main Zone of the Bushveld Complex, where the last voluminous influx of magma into the Bushveld Complex is thought to have occurred. In an attempt to constrain the Nd-isotopic composition of the magma added at the level of the Pyroxenite Marker, a total of 21 whole-rock samples from a borehole (BH7771) drilled on the Central Sector of the Eastern Limb of the Bushveld Complex were analysed for their Sr–Nd isotopic ratios. Modelling suggests that the added magma had a unique Sr (87Sr/86Sri = 0.7063–0.7067) and Nd (ƐNdi on the order of − 5.9) isotopic composition, distinct from any of the rocks constituting the layered sequence below the Pyroxenite Marker. Dispersion of data points around the modelled isotopic (melt–melt) mixing curves is interpreted to reflect the incorporation of minerals derived from either the incoming or resident magmas into individual rock layers occurring across the Pyroxenite Marker interval, either in response to the mixing of minerals settling through a stratified magma column, or potentially through the intrusion and mixing of crystal-laden magmas with unique isotopic compositions from a sub-Bushveld staging chamber.

Hf-Nd-Sr Isotopic Composition of the Tibetan Plateau Dust as a Fingerprint for Regional to Hemispherical Transport.

Large areas of arid regions in the Tibetan Plateau (TP) are undergoing desertification and subsequent aeolian emission and transport. The contribution of TP soils to the atmospheric aerosol burden in Asia and elsewhere is not known. Here, we use Hf, Nd, and Sr isotopes to distinguish the TP from other Asian dust-producing regions and compare the signatures to sediments in major dust sink regions. We found that the Hf-Nd-Sr isotopes of TP soils showed unique spatial signatures. From north to south, 87Sr/86Sr ratios gradually increased, while εNd and εHf values gradually decreased; from west to east, 87Sr/86Sr and εHf gradually increased, while εNd changed indistinctly. The Hf-Nd-Sr isotopic compositions of TP soils were controlled by four geographic isotope regions: the northern, southern, western, and eastern TP. Compared with Asian large deserts, the TP showed a unique isotopic composition, which together exhibited a significant spatial change across Asia. Compared to dust isotopes in prominent sink areas, we found that the TP is an important dust source to eastern TP glaciers, the Chinese Loess Plateau, South China Sea, Japan, and Greenland. This study provides clear isotopic evidence that the TP is a major aeolian contributor in the Northern Hemisphere and may have important implications for the global aeolian cycle.

Metal isotope signatures from lava-seawater interaction during the 2018 eruption of Kīlauea

The 2018 eruption of Kīlauea was associated with massive input of molten lava into the coastal ocean, which altered seawater chemistry and increased phytoplankton production. In seawater plumes advected away from the site of lava entry, we observed elevated concentrations of over a dozen metals relative to background seawater and unique isotopic compositions of Fe, Cu, Ni, Cd and Zn. The δ56Fe of iron released from lava was lower than basaltic, riverine and coastal iron from Hawaiʻi, but similar to observations of other high-temperature hydrothermal vent fluids. However, rapid precipitation led to only modest enrichments in dissolved iron (<10 nM), with increasing dissolved δ56Fe likely due to fractionation associated with ligand-mediated dissolution of particulate Fe. The isotopic composition of copper and nickel show evidence for two-endmember mixing between background seawater and a lava source. While the Ni isotopic endmember reflected basaltic δ60Ni, endmember δ65Cu, δ66Zn, and δ114Cd were isotopically lighter than basalt. We hypothesize that high diffusivity and volatility of chalcophile elements leads to strong kinetic fractionation in rapidly cooling lavas, similar to Cu, Zn and Cd isotopic patterns observed in tektites. The isotopic signatures of Cu and Ni observed during the 2018 eruption of Kīlauea far exceed their normal seawater range and may be useful for identifying large-scale lava input into ocean waters during the formation of large igneous provinces and other episodes of volcanism.

Using nitrogen concentration and isotopic composition in lichens to spatially assess the relative contribution of atmospheric nitrogen sources in complex landscapes

Reactive nitrogen (Nr) is an important driver of global change, causing alterations in ecosystem biodiversity and functionality. Environmental assessments require monitoring the emission and deposition of both the amount and types of Nr. This is especially important in heterogeneous landscapes, as different land-cover types emit particular forms of Nr to the atmosphere, which can impact ecosystems distinctively. Such assessments require high spatial resolution maps that also integrate temporal variations, and can only be feasibly achieved by using ecological indicators. Our aim was to rank land-cover types according to the amount and form of emitted atmospheric Nr in a complex landscape with multiple sources of N. To do so, we measured and mapped nitrogen concentration and isotopic composition in lichen thalli, which we then related to land-cover data. Results suggested that, at the landscape scale, intensive agriculture and urban areas were the most important sources of Nr to the atmosphere. Additionally, the ocean greatly influences Nr in land, by providing air with low Nr concentration and a unique isotopic composition. These results have important consequences for managing air pollution at the regional level, as they provide critical information for modeling Nr emission and deposition across regional as well as continental scales.

Global patterns and environmental controls of perchlorate and nitrate co-occurrence in arid and semi-arid environments

Natural perchlorate (ClO4−) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO4− compared to other major anions, its stability, or long-term variations in production that may impact the observed distributions. Our objectives were to evaluate the occurrence and fate of ClO4− in groundwater and soils/caliche in arid and semi-arid environments (southwestern United States, southern Africa, United Arab Emirates, China, Antarctica, and Chile) and the relationship of ClO4− to the more well-studied atmospherically deposited anions NO3− and Cl− as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO4− is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10−1 to 106μg/kg. Generally, the ClO4− concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO3− and ClO4− co-occur at molar ratios (NO3−/ClO4−) that vary between ∼104 and 105. We hypothesize that atmospheric deposition ratios are largely preserved in hyper-arid areas that support little or no biological activity (e.g. plants or bacteria), but can be altered in areas with more active biological processes including N2 fixation, N mineralization, nitrification, denitrification, and microbial ClO4− reduction, as indicated in part by NO3− isotope data. In contrast, much larger ranges of Cl−/ClO4− and Cl−/NO3− ratios indicate Cl− varies independently from both ClO4− and NO3−. The general lack of correlation between Cl− and ClO4− or NO3− implies that Cl− is not a good indicator of co-deposition and should be used with care when interpreting oxyanion cycling in arid systems. The Atacama Desert appears to be unique compared to all other terrestrial locations having a NO3−/ClO4− molar ratio ∼103. The relative enrichment in ClO4− compared to Cl− or NO3− and unique isotopic composition of Atacama ClO4− may reflect either additional in-situ production mechanism(s) or higher relative atmospheric production rates in that specific region or in the geological past. Elevated concentrations of ClO4− reported on the surface of Mars, and its enrichment with respect to Cl− and NO3−, could reveal important clues regarding the climatic, hydrologic, and potentially biologic evolution of that planet. Given the highly conserved ratio of NO3−/ClO4− in non-biologically active areas on Earth, it may be possible to use alterations of this ratio as a biomarker on Mars and for interpreting major anion cycles and processes on both Mars and Earth, particularly with respect to the less-conserved NO3− pool terrestrially.

Chlorine isotope homogeneity of the mantle, crust and carbonaceous chondrites

Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances. Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula and to calculate the relative proportions of Cl in the mantle and crust. Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same 37Cl/35Cl ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same delta37Cl value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition.

Pb-Sr-Nd Isotopic Systematics of Mantle-derived Rocks in the World

Based on more than 30000 Pb-Sr-Nd isotopic analyses of the basaltic rocks of different tectonic settings such as mid-ocean ridge, oceanic island, island arc and intra-plate environments both within continental and oceanic plates, which have been reported in literatures, the sources of magma for different types of basalts and the nature of the mantle are reviewed in this paper. The data suggest that mantle domains such as EM1, EM2 and HIMU that have unique isotopic compositions do not represent typical mantle but rather represent local heterogeneity in the mantle, possibly in the transitional zone between the upper and lower mantles. PREMA (previous mantle) is a common mantle domain for oceanic island basalts and inter-plate flood basalts. This type of mantle domain probably exists in the lower mantle. DUPAL-anomaly exists not only in the source region of mid-ocean basalts, but also in the source regions of oceanic island and island arc basalts, and flood basalts within oceanic plates where variations in different isotopes in the rocks are coupled. The isotopic systematics of flood basalts indicate that their sources include recycled crustal materials in the mantle, partial melts from lithosphere owing to decompressing melting, mantle-derived melts from the transition zone between the upper and lower mantles, and from the lower mantle with primitive or slightly depleted isotopic signatures. Pb isotopic systematics may provide unique evidence for the contribution of subducted materials. Pb isotopic compositions of volcanic rocks from the Andean arc suggest that these rocks are not related to the subduction of the Pacific oceanic plate beneath the Andes.

Hydrogeochemistry and groundwater circulation in the Xi’an geothermal field, China

Geothermal waters from the Tertiary aquifers located at 1000–3000 m beneath Xi’an city, Shaanxi Province, China, show unique isotopic composition as compared to local groundwaters from shallower Quaternary aquifers. Positive oxygen shifts of as much as 8‰ VSMOW are observed, while the corresponding δ 2H values remain essentially constant at about −80‰ VSMOW, which is significantly different from those of waters in the Quaternary aquifers with a mean δ 2H value of −60‰ VSMOW. The strong 18O shift is a result of isotope exchange between geothermal water and carbonate minerals such as calcite over a residence time of several thousand years up to 30,000 years, based on 14C dating. A comparison of the isotopic composition of geothermal waters with neighbouring groundwater units on both sides of the Guanzhong Basin indicates that the geothermal reservoirs are recharged by rain that falls on the northern slope of the Qinling Mountains, south of the Xi’an geothermal field, but not from the North Mountains to the north of the field. Based on chemical geothermometers the highest temperature estimated for the Tertiary aquifers of the Xi’an area is around 130 °C.

Changes in the lead isotopic composition of blood, diet and air in Australia over a decade: Globalization and implications for future isotopic studies

Source apportionment in biological or environmental samples using the lead isotope method, where there are diverse sources of lead, relies on a significant difference between the isotopic composition in the target media and the sources. Because of the unique isotopic composition of Australian lead, source apportionment has been relatively successful in the past. Over the period of a decade, the 206Pb/ 204Pb ratio for Australian (mainly female) adults has shown an increase from a geometric mean of 16.8–17.3. Associated with this increase, there has been a decrease in mean blood lead concentration from 4.7 to 2.3 μg/dL, or about 5% per year, similar to that observed in other countries. Lead in air, which up until 2000 was derived largely from the continued use of leaded gasoline, showed an overall increase in the 206Pb/ 204Pb ratio during 1993–2000 from 16.5 to 17.2. Since 1998 the levels of lead in air were less than 0.2 μg/m 3 and would contribute negligibly to blood lead. Over the 10-year period, the 206Pb/ 204Pb ratio in diet, based mainly on quarterly 6-day duplicate diets, increased from 16.9 to 18.3. The lead concentration in diet showed a small decrease from 8.7 to 6.4 μg Pb/kg although the daily intake increased markedly from 7.4 to 13.9 μg Pb/day during the latter part of the decade probably reflecting differences in demographics. The changes in blood lead from sources such as lead in bone or soil or dust is not dominant because of the low 206Pb/ 204Pb ratios in these media. Unless there are other sources not identified and analysed for these adults, it would appear that in spite of our earlier conclusions to the contrary, diet does make an overall contribution to blood lead, and this is certainly the case for specific individuals. Certain population groups from south Asia, south-east Asia, the Middle East and Europe (e.g. UK) are unsuitable for some studies as their isotopic ratios in blood are converging towards the increasing Australian values. The increases in blood 206Pb/ 204Pb ratio combined with globalization, which has resulted in the increases in 206Pb/ 204Pb ratio for diet, means that isotopic studies undertaken with a high degree of certainty of outcomes over a decade ago, are now considerably more difficult, not only in Australia but also in other countries where the isotopic differences are even less than in Australia.

Mars chronology: assessing techniques for quantifying surficial processes

Currently, the absolute chronology of Martian rocks, deposits and events is based mainly on crater counting and remains highly imprecise with epoch boundary uncertainties in excess of 2 billion years. Answers to key questions concerning the comparative origin and evolution of Mars and Earth will not be forthcoming without a rigid Martian chronology, enabling the construction of a time scale comparable to Earth's. Priorities for exploration include calibration of the cratering rate, dating major volcanic and fluvial events and establishing chronology of the polar layered deposits. If extinct and/or extant life is discovered, the chronology of the biosphere will be of paramount importance. Many radiometric and cosmogenic techniques applicable on Earth and the Moon will apply to Mars after certain baselines (e.g. composition of the atmosphere, trace species, chemical and physical characteristics of Martian dust) are established. The high radiation regime may pose a problem for dosimetry-based techniques (e.g. luminescence). The unique isotopic composition of nitrogen in the Martian atmosphere may permit a Mars-specific chronometer for tracing the time-evolution of the atmosphere and of lithic phases with trapped atmospheric gases. Other Mars-specific chronometers include measurement of gas fluxes and accumulation of platinum group elements (PGE) in the regolith. Putting collected samples into geologic context is deemed essential, as is using multiple techniques on multiple samples. If in situ measurements are restricted to a single technique it must be shown to give consistent results on multiple samples, but in all cases, using two or more techniques (e.g. on the same lander) will reduce error. While there is no question that returned samples will yield the best ages, in situ techniques have the potential to be flown on multiple missions providing a larger data set and broader context in which to place the more accurate dates.

Recycling oceanic crust: Quantitative constraints

Recycled ancient oceanic crust with variable amounts of aging, or inclusion of sediments of differing types and origins has often been invoked as a source for present‐day ocean island basalts (OIB), but the current evidence remains largely qualitative. Previous quantitative modeling has shown that much has to be learned in order to better understand the implications of crustal recycling on mantle heterogeneity. Here, we present new model calculations incorporating recent constraints on subduction‐zone processes and the composition of subducted sediments. Modeled compositions of the recycled oceanic crust vary widely as a function of the recycling age and composition of the oceanic crust. HIMU‐type sources can only be created by recycling igneous oceanic crust if it has undergone substantial modification during subduction. Although the required modifications are qualitatively consistent with dehydration processes in subduction zones, the many uncertainties prevent a precise estimate of the isotopic composition of ancient recycled igneous crust. Inclusion of sediments increases the isotopic variability and although the resulting Sr and Nd isotopic signatures can be similar to enriched mantle (EM) signatures, the Pb isotopic composition of EM‐type OIB is difficult to reconcile with the presence of sediment in their sources. The large variability of modeled compositions of the subducted crust suggests that if mantle heterogeneity is largely formed by crustal recycling, each OIB is likely to have a unique isotopic composition resulting from specific combinations of composition, age and subduction modification of the subducted crust. Given the variability of the recycled components, a small number of relatively well‐defined enriched compositions can only be explained if either the subduction processing of oceanic crust is a far better defined process than observation would seem to indicate, or, the intramantle disaggregation and mixing of compositionally diverse recycled materials is surprisingly efficient.

Ferro-andesites in the Grande Ronde Basalt: their composition and significance in studies of the origin of the Columbia River Basalt Group

Flows from the Grande Ronde Basalt of the Columbia River Basalt Group include several with the chemical composition of ferro-andesites. These flows have SiO2 &gt; 55%, MgO &lt; 4%, and also have higher Fe/Mg than the average value for Grande Ronde Basalt. They are also distinctly richer in Cs, Rb, K, Ba, La, Ce, Th, and U than the remainder of the Grande Ronde Basalt flows, and possess small negative Eu anomalies. Their Pb isotopic compositions define a mixing line with a negative slope on a 206Pb/204Pb versus 207Pb/204Pb plot. Their Nd isotopic compositions lie between 143Nd/144Nd = 0.51252 and 0.51264, and their Sr isotopic compositions lie between 87Sr/86Sr = 0.7055 and 0.7060. These values define the enriched end of the Columbia River Basalt Group spectrum on a Sr–Nd epsilon diagram (excluding the Saddle Mountains Basalt). These ferro-andesite flows also form a compositional end member of the Columbia River Basalt Group and are sufficiently distinctive to warrant special consideration. We compare them with lavas from other tholeiitic provinces. Petrogenetically, they can be related to the Grande Ronde Basalt low-Mg basalts by plagioclase fractionation, or by clinopyroxene fractionation in partially melted eclogites. However, the situation may not be that simple, as their unique isotopic compositions are closely related to those of parental mantle materials, perhaps thus requiring separate reservoirs and (or) sources. Extending this argument to other parts of the Columbia River Basalt Group suggests that the origin of these basalts may be in a system of comparatively small magma chambers in the uppermost mantle, frequently replenished from a variety of sources.

Leakage of industrial lead into the hydrocycle

Quantitative knowledge concerning the contamination effect by industrial Pb migrating through soils into groundwaters has been delineated in a special study carried out in a remote, high altitude mountain valley. Approximately 0.5 ton of industrial Pb has been added in past decades from the atmosphere via precipitation and dry deposition to the 3 km 2 area of lightly forested and open meadow soil lying within the 13 km 2 area of the rocky valley. Industrial Pb could be distinguished and its amounts quantitatively determined by use of its unique isotopic composition, which was different from natural Pb in meadow soil. Industrial Pb introduced into the canyon within snow was interacting and exchanging with the larger reservoir of industrial Pb accumulated in canyon soil. Lead in the snow-melt runoff had become attached to soil-derived colloids, and a mixture of industrial and natural particulate Pb was released from the soil to stream water and groundwater. The flux of Pb leached from the accumulated reservoir of industrial Pb in soil could be measured as it flowed through soil pathways into stream runoff waters draining the valley. Such leached industrial Pb comprised about 75% of the total Pb in stream runoff of snow-melt and 20% of the total Pb in stream runoff of groundwater.

The potential application of stable isotopes for distinguishing indigenous versus migrated hydrocarbons in a mature shale/sandstone sequence

Bitumens isolated from Kökelsumer Heide No. 1 corehole (Ruhr area, F.R.G.) are indicative of the problem of resolving contributions of indigenous versus migrated fluids. Within a depth interval of approximately 50 m, thermally mature shales containing Types II and III organic matter and a coal seam (1.2% R m) are all encountered, in addition to interbedded sands that are present in the upper portion of this interval. Presented here is an approach based on the unique isotopic compositions of indigenous bitumens, kerogens and migrating fluids which appears to enable the evaluation of the proportion of extracts which migrated from a source rock. Stable carbon isotope values of kerogens and of saturate and aromatic fractions of residual bitumens isolated from Kökelsumer Heide No. 1 and Reckelsumer Heide No. 2 corehole samples are used to estimate the relative contributions of the various sources to the bitumens. Preliminary results indicate that from 10% (shale sequences) to 100% (sandstone sequences) of the extractable materials (i.e. bitumens) could be characterized as a migrating fluid. Also, stable carbon and nitrogen isotope values for kerogens and coal samples from the Kökelsumer Heide corehole can be used to verify previous geochemical and microscopic evidence for the existence of distinct kerogen Types (I and II) in this corehole.

The petrogenesis of brines in Devonian potash deposits of western Canada

Recent mine-level floods in some potash mines in the Elk Point Basin of Saskatchewan, Canada, have demonstrated the need to identify accurately the source of water leaks so as to assist in remedial or preventative action. Most chemical constituents of the waters are inadequate tracers of the origin of these leaks because the concentrations of most elements change substantially during migration of the fluids to the mining level. In marked contrast to most of the chemical constituents dissolved in the water, oxygen and hydrogen isotopes are conservative elements of the water. Within the Elk Point Basin, δD- and δ 18O-values of basinal waters normally increase with depth because of mixing between trapped formation waters, and local surface waters such that the water in each aquifer within the basin generally has a unique isotopic composition. Floodwaters in the potash mines of Saskatchewan have chemical and stable isotopic compositions that indicate three different origins for mine-level fluids: (1) halite- and sylvite-saturated basinal brines from Devonian formations directly above the deposits, which are predominantly connate waters; (2) undersaturated waters of predominantly meteoric origin, from stratigraphically higher aquifers such as the Cretaceous Mannville Group; and (3) Ca-rich brines that may represent Devonian fluids associated with recrystallization of the evaporites. The salt-undersaturated formation waters most likely are directed to lower stratigraphic units through collapse structures or related features which may be reactivated through mining.

Stable isotope data of Bergslagen carbonates and their potential use for sulphide ore prospecting

Abstract A preliminary investigation of carbon and oxygen isotopes in ore-associated carbonates from Bergslagen, south-central Sweden, reveals a large spread in isotopic composition: δ13C ranges from - 7 to + 65%, and δ18O between + 4 and + 26% (rel. SMOW). However, each locality seems to be characterized by a unique isotopic composition. It is suggested that the isotopic composition of the carbonates originally had a uniform marine signature, and that the present variability in isotopic composition is due to secondary alteration effects. The extent of alteration, and consequently the observed isotopic compostion of the carbonates, is a function of the ore-forming activity and the post-depositional history of each district and it is thus suggested that carbon and oxygen isotope studies may be useful tools for sulphide ore prospecting.

Uranium-lead abundances and isotopic studies in the chondrites Richardton and Farmington

207Pb/ 204Pb- 206Pb/ 204Pb whole meteorite isochrons for Richardton (H5) and Farmington (L5) are presented and give Pb-Pb ages of 4.545 ± 0.010 and 4.620 ± 0.010 Ga respectively (errors ± 2σ). The Pb-Pb isochron for Farmington passes below the Can˜on Diablo troilite composition, which may therefore not be the initial Pb composition for this meteorite. All samples show an apparent excess radiogenic lead for single-stage (closed-system) evolution when Can˜on Diablo troilite is used for the initial lead composition. Evidence is presented to show that the apparent excess Pb cannot be explained by terrestrial contamination. There is no unique isotopic composition for initial lead that yields concordant ages at 4.55 Ga for all samples for either meteorite. The data likewise cannot be reconciled to Can˜on Diablo initial lead through any of the conventional two- and three-stage evolution models. The apparent excess Pb, with respect to a Can˜on Diablo troilite composition and a single-stage closed-system history, and the apparent inhomogeneous initial Pb isotopic compositions, appear to be real. This may be an indication that the U-Pb systems in these meteorites are disturbed, but this disturbance cannot be described consistently by any of the conventional episodic evolution models.

Gas Tag Identification of Failed Reactor Assemblies—III. Tag Ratios for the Fast Flux Test Facility Cores I through IV

Gas tagging consists of adding small amounts of gas with a unique isotopic composition for each assembly to nuclear reactor fuel and control assemblies. During subsequent irradiation, when any pin ...

Gas Tag Identification of Failed Fuel–I. Synergistic Use of Inert Gases

Gas tagging consists of the addition to nuclear reactor fuel pins of small amounts of gas having a unique isotopic composition for each assembly; when an assembly fails during subsequent irradiatio...