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The origin of 36Cl in the environment was investigated in this work. Together with its natural production due to cosmic rays, the anthropogenic input during nuclear weapon tests and due to the accident at Chernobyl nuclear power plant was considered. The hypothesis of the bomb-produced 36Cl recycling via the biosphere was proved experimentally. Water samples were collected from European, African, and Asian lakes and delivered to Technische Universität München. After a chemical treatment, ratio of 36Cl/Cl was measured with accelerator mass spectrometry in Garching. The stable chlorine concentration was measured chromatographically. The obtained 36Cl concentration was in the range from 0.6x107 at/l to 210x107 at/l. High 36Cl content in European lakes was assigned to the Chernobyl accident. The comparison of the 36Cl and 137Cs contamination showed that a 137Cs activity of 1 kBq m-2 corresponds to a 36Cl deposition of about 9x1010 atoms per square meter. The total 36Cl release from the Chernobyl accident was estimated to be 0.5±0.2 kg. A box model was used to describe the atmospheric transport of radionuclides. The latitudinal distributions of the cosmogenic and bomb-produced 36Cl were simulated. The 36Cl concentration in African and Asian lakes was used to normalize the stratospheric release of 36Cl from the near-water nuclear weapon tests. About 18% of the 36Cl produced in the ocean reached the stratosphere. A total stratospheric emission of 24±9 kg of 36Cl was obtained. The results of the modeling were in a good agreement with the measurements for most of the lakes. This fact was used to estimate unknown hydrological parameters of lakes. The groundwater age of two lakes with short flushing times: Ammersee and Chiemsee was determined. The closure age of Issyk-Kul Lake was estimated to be about 270,000 years. A part of the bomb 36Cl was considered to be stored in the biosphere and to be released as CH336Cl to the troposphere. An experimental setup to determine the 36Cl content in tropospheric CH3Cl was developed. The measurements performed in Kranzberger Forst showed that the mean global recycled 36Cl flux could be up to 70 at m-2s-1. The implementation of the recycling into the transport model explained the discrepancy of the simulated and measured 36Cl flux, previously observed in modern precipitation. Die Quellen von 36Cl in der Umwelt wurden untersucht. Die natürliche Produktion über kosmische Strahlung sowie die anthropogenen Freisetzungen bei den Atombomben-Tests und dem Tschernobyl Unfall wurden betrachtet. Rezirkulation von bomben-produziertem 36Cl über die Biosphäre wurde bewiesen. Wasserproben aus europäischen, afrikanischen und asiatischen Seen wurden gesammelt und an die Technische Universität München geliefert. Die Proben wurden chemisch aufbereitet und das 36Cl/Cl Verhältnis wurde mit Beschleunigermassenspektrometrie gemessen. Die Konzentration von stabilem Chlor wurde chromatographisch bestimmt. Die 36Cl Konzentrationen lagen im Bereich zwischen 0,6x107 at/l und 210x107 at/l. In europäischen Seen dominiert der Tschernobyl-Anteil von 36Cl. Die 36Cl und 137Cs Depositionen wurden verglichen. Eine 137Cs Aktivität von 1 kBq/m2 entspricht einem 36Cl Fallout von 9x1010 at/m2. Die gesamte 36Cl Freisetzung vom Tschernobyl Unfall wurde zu 0,5±0,2 kg abgeschätzt. Die atmosphärische Ausbreitung von Radionukliden wurde mit einem Boxen-Modell beschrieben. Die Breitengradabhängigkeit von kosmogenem und bomben-produziertem 36Cl wurde simuliert. Die stratosphärische Injektion von 36Cl aus den Kernwaffentests wurde über die 36Cl Konzentration in afrikanischen und asiatischen Seen normiert. Der stratosphärische Eintrag von 36Cl wurde zu 24±9 kg berechnet. Etwa 18% vom im Ozean produzierten 36Cl hat die Stratosphäre erreicht. Die gute Übereinstimmung zwischen den gemessenen und modellierten Werten wurde benutzt, um auf unbekannte hydrologische Parameter von Seen zurückzuschließen. Die Verweilzeit des Grundwassers in Ammersee und Chiemsee wurde berechnet. Das Alter vom abgeschlossenen See Issyk-Kul wurde zu 270000 a abgeschätzt. Ein Teil des bomben-produzierten 36Cl wurde in der Biosphäre gespeichert und wird als CH336Cl in die Troposphäre freigesetzt. Zum Sammeln von troposphärischem CH3Cl wurde ein Aufbau entwickelt und im Kranzberger Forst eingesetzt. Die obere Grenze für den mittleren globalen Fluss von rezirkuliertem 36Cl wurde zu 70 at/(m2s) bestimmt. Das Einführen der Rezirkulation in das Transportmodell erklärt die vorher beobachtete Diskrepanz zwischen den simulierten und gemessenen 36Cl Flüssen.

The {sup 36}Cl(n,p){sup 36}S and {sup 36}Cl(n,{alpha}){sup 33}P reaction cross sections have been studied with resonance neutrons at the linear accelerator GELINA of the IRMM in Geel (Belgium) and have been determined up to approximately 250 keV using the time-of-flight technique. In this energy region, 17 resonances were observed, whereas eight were identified before. For some resonances the resonance strength, the spin, and the total width could be determined. From the obtained cross section data, the MACS has been calculated by numerical integration. These updated MACS values were used in stellar models to trace the origin of the rare isotope {sup 36}S.

Chlorine is present as an impurity in the UO{sub 2} nuclear fuel. {sup 35}Cl is activated into {sup 36}Cl by thermal neutron capture. In case of interim storage or deep geological disposal of the spent fuel, this isotope is known to be able to contribute significantly to the instant release fraction because of its mobile behavior and its long half life (around 300000 years). It is therefore important to understand its migration behavior within the fuel rod. During reactor operation, chlorine diffusion can be due to thermally activated processes or can be favoured by irradiation defects induced by fission fragments or alpha decay. In order to decouple both phenomena, we performed two distinct experiments to study the effects of thermal annealing on the behaviour of chlorine on one hand and the effects of the irradiation with fission products on the other hand. During in reactor processes, part of the {sup 36}Cl may be displaced from its original position, due to recoil or to collisions with fission products. In order to study the behavior of the displaced chlorine, {sup 37}Cl has been implanted into sintered depleted UO{sub 2} pellets (mean grain size around 18 {mu}m). The spatial distribution of the implantedmore » and pristine chlorine has been analyzed by SIMS before and after treatment. Thermal annealing of {sup 37}Cl implanted UO{sub 2} pellets (implantation fluence of 10{sup 13} ions.cm{sup -2}) show that it is mobile from temperatures as low as 1273 K (E{sub a}=4.3 eV). The irradiation with fission products (Iodine, E=63.5 MeV) performed at 300 and 510 K, shows that the diffusion of chlorine is enhanced and that a thermally activated contribution is preserved (E{sub a}=0.1 eV). The diffusion coefficients measured at 1473 K and under fission product irradiation at 510 K are similar (D = 3.10{sup -14} cm{sup 2}.s{sup -1}). Considering in first approximation that the diffusion length L can be expressed as a function of the diffusion coefficient D and time t by : L=(Dt)1/2, the diffusion distance after 3 years is L=17 {mu}m. It results that there is a great probability for the chlorine contained in the UO{sub 2} grains to have reached the grain boundaries after 3 years, in the core of the fuel rod as well as at its periphery. Moreover, diffusion and concentration of chlorine at grain boundaries has been evidenced using SIMS mapping. Our results indicate therefore, that, during reactor operation and after, the majority of {sup 36}Cl is likely to have moved to grain boundaries, rim and gap. This fraction might then significantly contribute to the rapid or instant release of chlorine. This could have important consequences for safety assessment. During reactor operation, chlorine ({sup 35}Cl), an impurity of the nuclear fuel, is activated into {sup 36}Cl, a long lived mobile isotope. Because of its long half life and its mobility, this isotope may contribute significantly to the instant release fraction under disposal conditions. Thermal annealing of Cl implanted UO{sub 2} sintered pellets show that it is mobile from temperatures as low as 1273 K (E{sub a} = 4.3 eV). Chlorine diffusion induced by irradiation with fission products preserves a thermally activated contribution. The radiation induced defects significantly enhance chlorine migration. (authors)« less

The amount, spatial distribution, and velocity of water percolating through the unsaturated zone (UZ) at Yucca Mountain, Nevada, are important issues for assessing the performance of the proposed deep geologic repository for spent nuclear fuel and high-level radioactive waste. To help characterize the nature and history of UZ flow, isotopic studies were initiated in 1995, using rock samples collected from the Miocene ash-flow tuffs in the Exploratory Studies Facility (ESF), an 8-km-long tunnel constructed along the north-south extent of the repository block, and the Enhanced Characterization of the Repository Block (ECRB) Cross Drift, a 2.5-km-long tunnel constructed across the repository block (Figure 1-1, Sources: Modified from DOE 2002 [Figure 1-14] and USBR 1996). Scientists from Los Alamos National Laboratory (LANL) analyzed for chlorine-36 ({sup 36}Cl) in salts leached from whole-rock samples collected from tunnel walls and subsurface boreholes, and scientists from the U.S. Geological Survey (USGS) analyzed for isotopes of oxygen, carbon, uranium, lead, thorium, and strontium in secondary minerals collected from subsurface fractures and lithophysal cavities. Elevated values for ratios of {sup 36}Cl to total chloride ({sup 36}Cl/CL) at the level of the proposed repository indicated that small amounts of water carrying bomb-pulse {sup 36}Cl (i.e., {sup 36}Cl/Cl ratios more » greater than 1250 x 10{sup -15} resulting from {sup 36}Cl produced by atmospheric testing of nuclear devices during the 1950s and early 1960s) had percolated through welded and nonwelded tuffs to depths of 200 to 300 meters (m) beneath the land surface over the past 50 years. Because of the implications of short travel times to the performance of the proposed repository, the U.S. Department of Energy (DOE)/Office of Civilian Radioactive Waste Management (OCRWM), Office of Repository Development (ORD), decided to verify the {sup 36}Cl/Cl data with an independent validation study. DOE asked the USGS to design and implement a validation study that would include {sup 36}Cl and tritium ({sup 3}H) analyses. Core samples were taken from 50 new boreholes drilled across two zones in the ESF where a substantial number of samples with elevated {sup 36}Cl/Cl ratios had been identified previously. Also, core intervals from the Sample Management Facility (SMF) were acquired for water extraction and {sup 3H} analyses. This report documents the background and history of the validation study and presents the results of the {sup 36}Cl to total chloride ({sup 36}Cl/Cl) and {sup 3}H analyses. « less

Previous studies Los Alamos National Laboratory (LANL) found elevated ratios of chlorine-36 to total chloride (36Cl/Cl) in samples of rock collected from the Exploratory Studies Facility (ESF) at Yucca Mountain (YM). The data were interpreted as an indication that fluids containing “bomb-pulse” 36Cl reached the repository horizon in the ~50 years since the peak period of above-ground nuclear testing. Due to the significance of 36Cl data to conceptual models of unsaturated zone flow, the United States Geological Survey (USGS) implemented a study to validate the LANL findings. The USGS drilled new boreholes at select locations across zones where bomb-pulse ratios had previously been identified. The drill cores were analyzed at Lawrence Livermore National Laboratory (LLNL). Because consensus was not reached between the USGS/LLNL and LANL on several fundamental points including the presence or absence of bomb-pulse 36Cl, an evaluation by the University of Nevada, Las Vegas (UNLV), was initiated. The overall objectives of the UNLV study were to investigate the source of the validation study’s conflicting results, and to obtain additional data on bomb-pulse isotopes at the repository horizon. UNLV engaged in discussions with previous investigators, reviewed reports, and analyzed archived samples. UNLV also collected new samples of rock from the ESF, soil profiles from the surface of YM, and samples of seep water from inside the ESF. Samples were analyzed for 36Cl/Cl ratios, and 99Tc and 129I in select samples. A column experiment was conducted mimicking the passage of bomb-pulse 36Cl through YM tuff. The work faced several obstacles including an extended shutdown of the tunnel. Only one sample yielded a background corrected 36Cl/Cl ratio that was higher than the accepted bomb-pulse threshold (1250 x 10-15). Specimen 01034214 obtained from the Drill Hole Wash fault (19+33) had a ratio of 1590 ± 80 (1σ) x10-15, whereas the other separate sample from this fault zone yielded 1160 ± 50 (1σ) x 10-15. Three samples collected from Alcove 6 averaged 490 ± 100 (1σ) x10-15; a sample from Sundance Fault resulted in a ratio of 920 ± 60 (1σ) x10-15, and a sample from the Bow Ridge Fault produced 530 ± 20 (1σ) x10-15. The results are significant because: 1) they tend to be lower than LANL data for comparable samples, albeit in agreement with the range of data produced in the area, and 2) they show that a bomb-pulse 36Cl/Cl ratio was measured in rock collected at the repository horizon level by a second and independent group of investigators (UNLV). Because of time UNLV was not able to replicate the results, and these few data points are insufficient to draw major and definitive conclusions. Leachates of soil samples collected from the surface above the ESF yielded several ratios with bomb-pulse 36Cl, particularly for samples encompassing the wetting front. Soil samples collected above the south ramp, where there was limited soil coverage due to a large amount of rock outcrop, had relatively large ratios ranging from 2170 ± 110 (1σ) x10-15 to 5670 ± 350 (1σ) x10-15. Soil samples from profiles from above the north ramp ranged from 820 ± 70 (1σ) x10-15 to 2390 ± 160 (1σ) x10-15, which compare favorably with previous measurements near the site. Water seepage into the ESF south ramp and 36Cl standards made from NIST material were also analyzed. The standards were produced to have nominal 36Cl/Cl ratios (10-15) of 500, 2,500 and 10,000 and the results showed good agreement with the calculated ratios. The seepage samples ranged between 680 ± 40 (1σ) x10-15 to 1110 ± 40 (1σ) x10-15, consistent with that found for modern meteoric water, with a small bomb-pulse component. Bomb-pulse 36Cl may not have been incorporated in this fast-path water because the surface above the infiltration zone consists mostly of outcrop and the flow pathways have probably mostly been leached. 99Tc was measured in five of nine leaches of ESF rock but poor analytical recoveries and lack of data overlap with 36Cl limit interpretations of these data. The detection capability of the ICP-MS was insufficient for measuring 129I without preconcentration, and detection by AMS may be preferable. Experiments were conducted using bromide instead of chloride as a carrier, which is advantageous because it may eliminate the need for blank subtraction. ESF samples prepared using bromide had 36Cl/Cl ratios (x10-15) with acceptable levels of uncertainty (1σ): 720 ± 30 and 1250 ± 90 for Bow Ridge and Drill Hole Wash Faults, respectively. The result for the latter is noteworthy because it constitutes a second detection of a 36Cl/Cl bomb-pulse ratio at the site, albeit from a non-Q measurement. The source of the conflicting results between USGS/LLNL and LANL could not be determined. There was no evidence that the different AMS facilities were a source of the discrepancy between the results.

There is a continual supply of new experimental data that are relevant to the assessment of the potential impacts of nuclear fuel waste disposal. In the biosphere, the traditional assessment models are data intensive, and values are needed for several thousand parameters. This is augmented further when measures of central tendency, statistical dispersion, correlations and truncations are required for each parameter to allow probabilistic risk assessment. Recent reviews proposed values for 10-15 key element-specific parameters relevant to (36)Cl, (129)I, (222)Rn, (226)Ra, (237)Np and (238)U, and some highlights from this data update are summarized here. Several parameters for Np are revised downward by more than 10-fold, as is the fish/water concentration ratio for U. Soil solid/liquid partition coefficients, Kd, are revised downward by 10-770-fold for Ra. Specific parameters are discussed in detail, including degassing of I from soil; sorption of Cl in soil; categorization of plant/soil concentration ratios for U, Ra and Np; Rn transfer from soil to indoor air; Rn degassing from surface water; and the Ca dependence of Ra transfers.

In 1991, the U.S. Geological Survey collected a 160-meter (m) ice core from the Upper Fremont Glacier (43°07′N, 109°36′W) in the Wind River Mountain Range of Wyoming in the western United States [1]. In 1994–1995, ice from this core was processed at the National Ice Core Laboratory in Denver, Colorado, and analyzed for chlorine-36 (36Cl) by accelerator mass spectrometry at PRIME Laboratory, Purdue University. A tritium bomb peak identified in the work by [1] was used as a marker to estimate the depth of bomb-produced 36Cl. Tritium concentrations ranged from 0 tritium units (TU) for older ice to more than 300 TU at 29 m below the surface of the glacier, a depth that includes ice that was deposited as snow during nuclear-weapons tests through the early 1960's. Maximum 36Cl production during nuclear-weapons tests was in the late 1950's; therefore, the analyses were performed on ice from a depth of 29.8 to 32 m. Calculated flux for 36Cl in ice deposited in the late 1950's ranged from 1.2 ± 0.1 × 10−1 atoms/cm2 s for ice from 29.8 to 30.4 m, to 2.9 ± 0.1 × 10−1 atoms/cm2 s for ice from 31.5 to 32.0 m. Ice samples from a depth of 104.7 to 106.3 m were selected to represent pre-weapons tests 36Cl flux. Calculated flux for 36Cl in this deeper ice was 4.6 ± 0.8 × 10−3 atoms/cm2 s for ice from 104.7 to 105.5 m and 2.0 ± 0.2 × 10−2 atoms/cm2 s for ice from 105.5 to 106.3 m. These flux calculations from the Upper Fremont Glacier analyses are the first for bomb-produced 36Cl in ice from a mid-latitude glacier in North America. It may now be possible to fully quantify the flux of 36Cl from nuclear-weapons tests archived in mid-latitude glacial ice and to gain a better understanding of the distribution of 36Cl and other cosmogenic nuclides.

The present paper proposes a new detection system which can be added to existing or future 3 MV AMS tandems to provide 36 Cl measurements at AMS sensitivities. The principles are as follows: A small 3 MV terminal tandem accelerates ions in the 4 + charge state to an energy of ∼ 15 MeV. At this energy, the ions are mass analyzed, stripped a second time and post-acceleration analyzed to select only those mass-36 particles in the 7 + charge state. Following this selection, the ions are directed into a conventional ionization detector located within a high voltage terminal that is maintained at an electric potential of ∼ −3 MV. In this final acceleration stage, 21 MeV is added to the energy of the ions for a final energy of ∼ 36 MeV. Such a detection arrangement combines well-established ion chamber technology and straightforward Van de Graaff high voltage technology with modern data transmission techniques.

A 6-month soil column experiment was conducted to compare the upward migration and plant uptake of radiochlorine and radioiodine from shallow, near-surface contaminated water tables. Both fixed and fluctuating water tables were studied. After 6 months, (36)Cl activity concentrations were relatively uniform throughout the soil profile apart from an accumulation at the soil surface, which was especially marked under a fluctuating water table scenario. In contrast, (125)I (a surrogate for (129)I) tended to accumulate at the boundary between the anoxic conditions at the base of the column and the oxic conditions above, due to its redox-dependent sorption behaviour. The uptake of (36)Cl by perennial ryegrass was much greater than that of (125)I due to its greater migration into the rooting zone and its ready availability in soil solution. In the context of radioactive waste disposal, where these radionuclides may potentially be released into groundwater, (36)Cl would be expected to present a greater potential for contamination of the biosphere than (129)I.

Chemical separation procedures were developed that allow isolating the iodine, chlorine, aluminium, and beryllium fraction from lead targets irradiated with protons in an energy range up to 2.6 GeV. The cross sections of the four nuclides 10Be, 26Al, 129I, and 36Cl were determined; their excitation functions were calculated and compared with theoretical predictions developed within the HINDAS collaboration (EC 5th framework).

A survey is given about efforts undertaken during the HINDAS project to investigate the energy dependence of residual nuclide production by proton‐induced reactions from thresholds up to 2.6 GeV. For proton‐induced reactions, our experiments aimed to further develop and complete the cross‐section database that was established by our collaboration in recent years. It was extended to the heavy‐target elements Ta, W, Pb, and Bi for energies up to 2.6 GeV. In addition, new measurements for the target element iron were performed up to 2.6 GeV and for natural uranium for energies from 21 MeV to 69 MeV. For the target element lead, a comprehensive set of excitation functions published recently was completed by AMS‐measurements of cross sections for the production of the long‐lived radionuclides Be‐10, Al‐26, Cl‐36, and I‐129 and by mass spectrometric measurements for stable and radioactive rare gas isotopes of He, Ne, Ar, Kr, and Xe. Comprehensive tests of the nuclear‐reaction codes TALYS and INCL4+ABLA, which were developed within the HINDAS project, were performed with the new experimental results over the entire energy range.

Measurements of radiochlorine ({sup 36}Cl), radiogenic noble gases ({sup 4}He and {sup 40}Ar), and stable chlorine isotope ratios were obtained to assess the residence time of groundwater in the Nubian Aquifer of the Western Desert of Egypt. Measured {sup 36}Cl/Cl ratios yield apparent residence times from {approx}0.2 to 1.2 x 10{sup 6} years in the deep (600-1200 m) groundwater (assuming constant Cl) and {le} 0.16 x 10{sup 6} years in the shallow (

Measurements of 81Kr/Kr in deep groundwater from the Nubian Aquifer (Egypt) were performed by a new laser-based atom-counting method. 81Kr ages range from \~2x10^5 to ~1x10^6 yr, correlate with 36Cl/Cl ratios, and are consistent with lateral flow of groundwater from a recharge area near the Uweinat Uplift in SW Egypt. Low delta-2H values of the 81Kr-dated groundwater reveal a recurrent Atlantic moisture source during Pleistocene pluvial periods. These results indicate that the 81Kr method for dating old groundwater is robust and such measurements can now be applied to a wide range of hydrologic problems.

Two long-lived halogen radionuclides (36Cl, T1/2 = 301 kyr, and 129I, T1/2 = 15.7 Myr) have been studied by means of Accelerator Mass Spectrometry (AMS) at the Uppsala Tandem Laboratory. The 36Cl measurements in natural samples using a medium-sized tandem accelerator (~1 MeV/amu) have been considered. A gas-filled magnetic spectrometer (GFM) was proposed for the separation of 36Cl from its isobar, 36S. Semi-empirical Monte-Carlo ion optical calculations were conducted to define optimal conditions for separating 36Cl and 36S. A 180° GFM was constructed and installed at the dedicated AMS beam line. 129I has been measured in waters from the Arctic and North Atlantic Oceans. Most of the 129I currently present in the Earth's surface environment can be traced back to liquid and gaseous releases from the nuclear reprocessing facilities at Sellafield (UK) and La Hague (France). The anthropogenic 129I inventory in the central Arctic Ocean was found to increase proportionally to the integrated 129I releases from these reprocessing facilities. The interaction and origin of water masses in the region have been clearly distinguished with the help of 129I labeling. Predictions based on a compartment model calculation showed that the Atlantic Ocean and deep Arctic Ocean are the major sinks for the reprocessed 129I. The variability in 129I concentration measured in seawater along a transect from the Baltic Sea to the North Atlantic suggests strong enrichment in the Skagerrak–Kattegat basin. The 129I inventory in the Baltic and Bothnian Seas is equal to ~0.3% of the total liquid releases from the reprocessing facilities. A lake sediment core sampled in northeastern Ireland was analyzed for 129I to study the history of the Sellafield releases, in particular the nuclear accident of 1957. High 129I concentration was observed corresponding to 1990 and later, while no indication of the accident was found. The results of this thesis research clearly demonstrate the uniqueness and future potential of 129I as a tracer of processes in both marine and continental archives.

[1] The chloride mass balance (CMB) method for estimating groundwater recharge is economic and effective, provided that the hydrological conditions for its applications are met and the modeling parameters are known. However, modeling parameters such as precipitation and Cl− deposition rates vary temporally, most notably as a result of the climatic changes from late Pleistocene to Holocene. The temporal variability of atmospheric Cl− input and annual precipitation were considered in this study by using a discrete steady state CMB model with different parameters for late Pleistocene and Holocene. Cl− deposition rates, estimated from 36Cl data, were lower in late Pleistocene than Holocene at Yucca Mountain, Nevada, but higher in late Pleistocene than Holocene at Black Mesa, Arizona. Paleoclimate proxies at both Yucca Mountain and Black Mesa point to higher precipitation rates in late Pleistocene than Holocene. The resulting average recharge estimates for Black Mesa are 9 ± 5 mm/yr for Holocene and 35 ± 22 mm/yr for late Pleistocene. Local recharge rates at Yucca Mountain were estimated from the 36Cl/Cl ratios and Cl− concentrations in perched waters. The estimated recharge for Yucca Mountain is 5 ± 1 mm/yr for Holocene and 15 ± 5 mm/yr for late Pleistocene. These recharge rates are comparable to results of independent numerical groundwater flow models and watershed-scale infiltration models at Black Mesa and Yucca Mountain, respectively.

Scarp morphology evolution has commonly been used to estimate the timing of fault-scarp rupture events. However, rates of scarp degradation depend strongly on the geomorphic diffusivity, a parameter that is difficult to constrain independently. This difficulty may lead to large uncertainties in the estimated ages of rupture events. In this study, we have coupled the accumulation of the cosmogenic nuclide Cl-36 to a model for scarp morphology in order to constrain the value of the geomorphic diffusivity and thus determine a more accurate rupture chronology than a rupture history based solely on scarp morphology. We measured depth profiles of Cl-36 accumulated in situ within alluvial sediments beneath the surface of the Socorro Canyon fault scarp in central New Mexico. The material analyzed consisted of similar to150 individual gravel clasts from each depth interval, amalgamated into a single sample. The alluvium was sampled in three vertical profiles similar to4 m deep. The first profile was similar to1.5 m downslope of the fault plane on the hanging wall, the second similar to1.5 m upslope of the fault plane on the footwall, and the third similar to27 m upslope of the fault plane on the footwall. The third profile, which served as a control, and which soil geomorphic evidence indicated was beneath a stable surface, showed a simple exponential Cl-36 profile from which a depositional age of 122 +/- 18 ka was calculated. The second profile (on the footwall) showed a Cl-36 deficit relative to the control profile, indicating net erosion. The first profile (on the hanging wall) showed a Cl-36 excess relative to the control profile, indicating net deposition. Stratigraphic evidence in the hanging wall indicated two rupture events prior to the Late Holocene. We modeled the accumulation of Cl-36 in the vicinity of the scarp, simulating erosional redistribution using a diffusion equation for scarp morphology. The model accounted for redistribution of Cl-36 along with the sediment and the effects of the changing fault-scarp morphology on the Cl-36 production. By matching both the observed hanging-wall and footwall Cl-36 profiles to profiles calculated by the model, as well as the observed topographic profile, we obtained ages of 92(-13)(+16) and 28(-23)(+18) ka for the two ruptures. The results of our study indicate that cosmogenic nuclides can be useful in constraining rupture chronologies of fault scarps in alluvium. (C) 2003 Elsevier B.V. All rights reserved.

This study tested whether isotope measurements of surface water and dissolved constituents in surface water could be used as tracers of non-point source pollution. Oxygen-18 was used as a water tracer, while carbon-14, carbon-13, and deuterium were tested as tracers of DOC. Carbon-14 and carbon-13 were also used as tracers of dissolved inorganic carbon, and chlorine-36 and uranium isotopes were tested as tracers of other dissolved salts. In addition, large databases of water quality measurements were assembled for the Missouri River at St. Louis and the Sacramento-San Joaquin Delta in California to enhance interpretive results of the isotope measurements. Much of the water quality data has been under-interpreted and provides a valuable resource to investigative research, for which this report exploits and integrates with the isotope measurements.

This analysis is governed by the Office of Civilian Radioactive Waste Management (OCRWM) Analysis and Modeling Report Development Plan entitled ''Geochemical and Isotopic Constraints on Groundwater Flow Directions, Mixing and Recharge at Yucca Mountain'' (CRWMS MO (2) Determine the timing of the recharge from stable isotopes such as deuterium ({sup 2}H) and oxygen-18 ({sup 18}O), which are known to vary over time as a function of climate, and from radioisotopes such as carbon-14 ({sup 14}C) and chlorine-36 ({sup 36}Cl); (3) Determine the magnitude of recharge from relatively conservative tracers such as chloride and/or groundwater age and unsaturated-zone thickness; (4) Correct {sup 14}C ages for possible dilution of radiocarbon by calcite fracture coatings using geochemical reaction models; and (5) Establish mixing relations between waters from different source areas using relatively conservative species such as {sup 2}H and {sup 18}O or chloride and sulfate, and evaluate if inferred flow paths and mixing relations are reasonable based on chemical reactions required to reproduce the observed water chemistry. The analysis presented in this report is appropriate for the intended use described above. This analysis is not directly related to the principal factors, or other factors, for the post-closure safety case, nor is it used directly in calculations or analyses that provide estimates of the effects of potentially disruptive processes and events, as described in AP-3.15Q, Managing Technical Product Inputs.« less

A distinct peak has been discovered in the 36 Cl data from the GRIP ice core between the Dansgaard Oeschger (D–O) events 6 and 7 at approximately 32 kyr BP. This peak can be attributed to a minimum of the geomagnetic dipole field associated with the Mono Lake event. Since the 36 Cl peak reflects a higher production rate of all cosmogenic radionuclides, it has an impact on the 14 C dating of the last ice age. Furthermore, it provides an additional time marker similar to a peak found earlier corresponding to the Laschamp event at approximately 39 kyr BP.

The purpose of this report is to describe the calculated contribution to ground water of natural, in situ produced 36Cl in the eastern Snake River Plain aquifer and to compare these concentrations in ground water with measured concentrations near a nuclear facility in southeastern Idaho. The scope focused on isotopic and chemical analyses and associated 36Cl in situ production calculations on 25 whole-rock samples from 6 major water-bearing rock types present in the eastern Snake River Plain. The rock types investigated were basalt, rhyolite, limestone, dolomite, shale, and quartzite. Determining the contribution of in situ production to 36Cl inventories in ground water facilitated the identification of the source for this radionuclide in environmental samples. On the basis of calculations reported here, in situ production of 36Cl was determined to be insignificant compared to concentrations measured in ground water near buried and injected nuclear waste at the INEEL. Maximum estimated 36Cl concentrations in ground water from in situ production are on the same order of magnitude as natural concentrations in meteoric water.

Development and testing of conceptual flow and transport models for hydrologic systems are strengthened when natural environmental tracers are incorporated into the process. One such tracer is chlorine-36 ({sup 36}Cl, half-life, 301,000 years), a radioactive isotope produced in the atmosphere and carried underground with percolating groundwater. High concentrations of this isotope were also added to meteoric water during a period of global fallout from atmospheric testing of nuclear devices, primarily in the 1950s. This bomb-pulse signal has been used to test for the presence of fast transport paths in the unsaturated zone at Yucca Mountain and to provide the basis for a conceptual model for their distribution. Yucca Mountain is under investigation by the US Department of Energy as a potential site at which to host an underground high-level radioactive waste repository. Under wetter climatic conditions, fast-flow pathways will respond quickly to increases in infiltration and have the potential to become seeps in the tunnel drifts. The {sup 36}Cl data are also being used in numerical flow and transport models to establish lower bounds on infiltration rates, estimate ground water ages, and establish bounding values for hydrologic flow parameters governing fracture transport.

The fall-out of cosmogenic 36Cl was determined by measuring the 36 Cl Cl ratios in old wines from the Rheingau in Germany [1]. The measured 36Cl/Cl ratios from the prebomb samples were compared with the sun spot numbers which are correlated to the solar cycle. A correlation between the sun spot number and the 36 Cl Cl ratios in the samples could not yet be confirmed.

Cosmogenic chlorine-36 reveals dates of the multiple prehistoric earthquakes that have produced a scarp on the Hebgen Lake fault. Apparent chlorine-36 ages are stratigraphically correct, follow a predicted theoretical pattern, and produce geologically reasonable model ages of 24, 20, 7.0, 2.6, 1.7, and 0.4 thousand years ago. This result demonstrates the feasibility of using cosmogenic chlorine-36 to extract paleoearthquake records from bedrock fault scarps.

The isotopic ratios of {sup 36}Cl/Cl are used in conjunction with geologic interpretation and numerical modeling to evaluate flow and transport pathways, processes, and model parameters in the unsaturated zone at Yucca Mountain. By synthesizing geochemical and geologic data, the numerical model results provide insight into the validity of alternative hydrologic parameter sets, flow and transport processes in and away from fault zones, and the applicability of {sup 36}Cl/Cl ratios for evaluating alternative conceptual models.

The LOREX‐ 205Tl solar neutrino experiment is designed to measure the solar neutrino flux integrated over the last few million of years using lorandite (TlAsS2) minerals from Allchar mine (Macedonia), by measuring the 205Pb content resulting from neutrino capture in 205Tl. The mean depth of the sample has to be determined by measuring the depth dependent cosmic ray induced production of isotopes 10Be, 26Al, 36Cl and 53Mn to evaluate the background 205Pb contributions. The basic idea is to accelerate the beams of above isotopes to energies required to obtain the fully stripped ions and separate them employing the resulting difference in q/m ratios.

Muon capture isotope detection (MuCID) is a non-destructive detection (assay) of composite and impurity nuclear isotopes by measuring γ rays following muon capture reaction products. Several nuclear isotopes are produced by muon capture reactions such as (μ, xn γ) with \(x = 0\), 1, 2, 3, and so on, and some of them are radioactive isotopes. The isotopes of the interest are identified by measuring γ rays characteristic of the reaction products by means of high-sensitivity Ge detectors. Composite and impurity nuclear isotopes of the orders of microgram–nanogram and ppm–ppb are investigated. The feasibility and the sensitivity of MuCID were shown experimentally by using μ capture reactions on Mo isotopes at MuSIC in RCNP. MuCID is used to study nuclear isotopes of astro-nuclear and particle physics interests and those of geological and historical interests.

Chlorine-36 has been identified as a potential source of radiological risk in the disposal of nuclear fuel waste. The radioisotope 36Cl (t1/2 = 3 × 1O5 a) is produced by neutron activation of Cl impurities in UO2 fuel. The total average Cl impurity level in four unirradiated CANDU UO2 fuel samples was 2.3 ± 1.1 ppm. ORIGEN-S calculations using a 5 ppm Cl impurity in a CANDU fuel resulted in a 36Cl activity comparable to the activity of 129I and 14C produced in the fuel thus requiring 36Cl to be considered in disposal risk assessments. The “instant release” of 36Cl from the gap and grain boundary regions of the fuel to solution was measured by leaching both clad fuel and fuel samples crushed to grain-sized particles. The 36Cl concentration was measured by Accelerator Mass Spectrometry. The 36Cl releases from fuel samples taken from 8 different fuel bundles ranged from 0.5% to 20.4% of the total 3 Cl inventory over a leaching period of 32 days. The 36Cl released was found to correlate with the stable Xe gas release, the fuel burnup and the linear power rating (LPR). For a typical CANDU fuel with an LPR of -42 kW/m, the “instant release” of 36Cl would be about 5% of the total inventory.

Chlorine-36, including the natural cosmogenic component and the component produced during atmospheric nuclear testing in the 1950's and 1960's (bomb pulse), is being used as an isotopie tracer for groundwater infiltration studies at Yucca Mountain, a potential nuclear waste repository. Rock samples have been collected systematically in the Exploratory Studies Facility (ESF), and samples were also collected from fractures, faults, and breccia zones. Isotopie ratios indicative of bomb-pulse components in the water (36Cl/Cl values > 1250 × 10-15), signifying less than 40-yr travel times from the surface, have been detected at a few locations within the Topopah Spring Tuff, the candidate host rock for the repository. The specific features associated with the high 36Cl/Cl values are predominantly cooling joints and syngenetic breccias, but most of the sites are in the general vicinity of faults. The non-bomb pulse samples have 36Cl/Cl values interpreted to indicate groundwater travel times of at least a few thousand to possibly several hundred thousand years. Preliminary numerical solute-travel experiments using the FEHM (Finite Element Heat and Mass transfer) code demonstrate consistency between these interpreted ages and the observed 36Cl/Cl values but do not validate the interpretations.

Radioactive waste management practices at the U.S. Department of Energy`s Idaho National Engineering Laboratory (INEL) in Idaho have introduced {sup 36}Cl (T{sub 1/2} = 301,000 yr) into the Snake River Plain aquifer underlying the site. The {sup 36}Cl is believed to originate from neutron activation of stable {sup 35}Cl in nuclear fuels (principally) and in reactor cooling/process water. Wastewater releases of {sup 3}H at the INEL have been documented by the site operators for the period 1952 to 1988. During this time, approximately 1.2 PBq of {sup 3}H (30,000 Ci) were introduced to the subsurface through disposal wells and seepage ponds. By sampling a number of monitoring and production wells downgradient from points of introduction, {sup 3}H movement and dispersion in the groundwater have been documented by the U.S. Geological Survey. The present report uses these historical {sup 3}H release and monitoring data to choose hydrologic parameters (matrix porosity and plume penetration depth) that produce concordance between the {sup 3}H release estimates and the inventory calculated from measurements of {sup 3}H in the subsurface. These parameters are then applied to {sup 36}Cl isopleths to generate an estimated {sup 36}Cl inventory in the subsurface. Using assumptions about irradiation times, neutron fluxes, and total fuel processed, as little as 23 g of stable chloride impurity in fuel elements would be adequate to produce the amount of {sup 36}Cl estimated to be in the groundwaters underlying the site. The highest atom concentration of {sup 36}Cl measured onsite (222x10{sup 10} atoms 1{sup -1}) corresponds to an activity level of {approximately}4 pCi 1{sup -1} and represents 0.2 percent of the U.S. Environmental Protection Agency`s (EPA) drinking water standard for this radionuclide (2000 pCi 1{sup -1}).

This report discusses isotope abundance measurements made on a collection of groundwater samples from the Orange County Water District. The water samples were collected in May, 1994 as part of a preliminary study conducted by LLNL to assess the feasibility of tracing and dating reclaimed water used in the Talbert Injection Barrier. A set of samples were collected both near to and far from the barrier and also at different depths in available monitoring wells. A variety of elements were selected for isotopic analysis; hydrogen (tritium), helium, neon, carbon, chlorine and strontium. The tritium abundance combined with the {sup 3}He and {sup 20}Ne abundance provides a method for age dating young (< 40 yr.) groundwater. The abundance of {sup 14}C provides an age dating technique for older (1,000--50,000 yr.) groundwater. The concentrations of {sup 36}Cl and {sup 87}Sr/{sup 86}Sr give information on sea water mixing and water-rock chemical interactions.

A variety of physical processes affect solute concentrations within catchment waters. The isotopic compositions of the solutes can indicate which processes have determined the observed concentrations. These processes together constitute the physical history of the water, which is one of the primary concerns in hydrology. Many groundwater solutes are derived as a result of interaction between the water and the rock and/or soil within the system. These are termed {open_quotes}lithogenic{close_quotes} solutes. The isotopic compositions of these solutes provide information regarding rock-water interactions. Many other solutes have their isotopic compositions determined both internally and externally to the catchment system. Important members of this group include solutes that have isotopic compositions produced by atomic particle interactions with other nuclides. The source of the atomic particles can be cosmic radiation (producing {open_quotes}cosmogenic{close_quotes} nuclides in the atmosphere and land surface), anthropogenic nuclear reactions (producing {open_quotes}thermonuclear{close_quotes} nuclides), or radioactive and fission decay of naturally-occurring elements, such as U and Th (producing {open_quotes}in-situ{close_quotes} lithogenic nuclides in the deep subsurface). Current language usage often combines all of the atomic particle-produced nuclides under the heading {open_quotes}cosmogenic nuclides{close_quotes}, and for simplicity we will often follow that usage, although always clearly indicating which variety is being discussed. This paper addresses the processes that affect the lithogenic and cosmogenic solute compositions in groundwater, and how these compositions can therefore be used in integrative ways to understand the physical history of groundwater within a catchment system.

A comprehensive isotope data base of the NTS groundwaters collected during FY 92-93 is presented with preliminary interpretations. Multiple samples were collected from over 30 sites on pumped wells and open-holes by wireline bailing. Field water level measurements indicate essentially a bimodal distribution separated by water levels at higher elevations (e.g. Pahute Mesa) from water levels of lower elevations (e.g. Yucca and Frenchman Flats). Down hole temperature measurements have confirmed anomalous temperature gradients in the eastern Yucca Flat area and on Pahute Mesa, where horizontal temperature gradients up to 0.33{degrees}F/100ft are found. Consistent with previous reports by others, the major ion geochemistry of the NTS groundwater are dominated by Na-K-HCO{sub 3} and Ca-Mg-HCO{sub 3} water types, where the Na-rich water appears to be related to dissolution in the volcanic tuffs and the Ca-rich water to the Paleozoic carbonates. Increases in dissolved Si also seems to be indicative of groundwater that resides in the volcanic tuffs. Processes controlling the Na/Ca ratios are complex and may include ion exchange reactions with clays, evaporative concentration in the vadose zone, and lithological heterogeneities in addition to simple differential dissolution between the volcanic tuffs and the Paleozoic carbonates. Apparent {sup 14}C ages range between 4000 and 38,000 years for groundwaters at the NTS. The uncertainty is large for exact age determinations at this time. The {sup 14}C abundance decreases with increased dissolved HCO{sub 3}, and {sup 13}C suggests dissolution of the ``dead`` Paleozoic carbonates significantly influence the ages, but more work is needed to investigate the influence of vadose zone carbonate.

Summary Helium isotope and concentration characteristics were determined for a suite of groundwater samples from the Amadeus Basin in Central Australia. Two study areas include a wellfield south of Alice Springs, and the Dune Plains and Mututjulu aquifers near Uluru. Measurements of 36Cl/Cl and 14C on the same sample suite enable us to assess the relative applicability of the three groundwater chronometers over a range of anticipated groundwater residence times (ages), and to investigate possible causes of discordant ‘ages’ derived from the different groundwater dating techniques. Results from the analyses of 39 groundwater samples reveal helium-4 (4He) concentrations that range from 0.80 to 98.8 (×10−7 cm3 STP g−1 H2O) in the Alice Springs samples, and from 0.47 to 65.6 (×10−7 cm3 STP g−1 H2O) in the Uluru samples. 4He concentrations yield uncorrected groundwater residence times (i.e. time since recharge) of between modern to >2500 ka (near Alice Springs) and modern to 1600 ka (near Uluru) assuming an effective porosity of 20%, and uranium and thorium contents of 1.7 and 6.1 ppm, respectively. 36Cl/Cl ratios on the same samples range from 93 to 158 (×10−15) (near Alice Springs) and from 80 to 335 (×10−15) (near Uluru) representing groundwater residence times near Alice Springs from modern to >200 ka, and from modern to >300 ka near Uluru. Percent modern carbon (pmc) on the same samples ranged from 64.9 to 12.5 pmc near Alice Springs, and from 93.5 to 30 ka. For the Amadeus Basin groundwater samples, the 4He method (uncorrected) over-estimates groundwater residence time compared to 36Cl and 14C techniques. This implies the presence of an extraneous He component or basal flux of He (J0). To reconcile groundwater 4He and 14C residence times, it is necessary to adopt J0 values between 0 and 30 (×10−8) cm3 STP He cm−2 a−1 which supplements in situ produced He within the aquifer. Adoption of J0 values over this range lowers 4He residence times relative to 36Cl and produces closer agreement between the 4He and 14C chronometers. The extraneous He component (basal flux) in Amadeus Basin samples is dominated by radiogenic crustal 4He without a detectable amount of mantle-derived 3He. We conclude that the stable tectonic regime, albeit with the presence of major faults within the basin, inhibits the input of mantle volatiles to the groundwater system so that in this region, diffusion is the dominant transport mechanism for He in the crust.

The bluestones of Stonehenge on Salisbury Plain continue to attract controversy. New dates on Stonehenge material using the Chlorine-36 method have been reported as evidence that the bluestones were moved from their Welsh sources by human transport, not by glaciation. Here Olwen Williams-Thorpe and colleagues, who have argued for the glacial transport theory, show that the Chlorine-36 dates have been misinterpreted.

[1] We use reactive transport modeling to consider how diffusion and hydrodynamic dispersion, cross-formational flow, and subsurface production affect the steady state distribution in flow regimes of the radioactive isotope 36Cl, and the relationship of the isotope distribution to groundwater residence time, or “age.” The isotope forms naturally in the atmosphere, dissolves in rainwater, and then decays in the subsurface with a half-life of ∼301,000 years; hence it is important for age dating very old groundwater. In a simple flow regime composed of an aquifer confined above and below by aquitards, isotopic age may correspond rather well with a groundwater's “piston flow” age. This correspondence is favored where the aquifer is thick, cross-formational flow is insignificant, salinity is low, and the diffusion coefficient within the aquitards is small. The maximum dateable age, however, is somewhat smaller than expected from the isotope's half-life. Owing to the effect of “dead” chloride, dating based on isotope abundance (the 36Cl/Cl ratio) may be less accurate than that based on 36Cl concentration. Cross-formational flow can strongly affect the 36Cl distribution and abundance, preventing the rates and even direction of flow within an aquifer from being interpreted using the piston flow model. Where salinity is moderate or high, the isotope distribution is controlled by subsurface production, and dating on the basis of the decay of atmospheric 36Cl is not possible. In models of simple flow regimes the 36Cl method fails to predict groundwater age accurately where groundwater chlorinity exceeds ∼75–150 mg kg−1. Reactive transport models hold considerable promise for improving interpretation of the rates and patterns of groundwater flow from radioisotope distributions.

A consortium of accclerator-mass-spectrometry (AMS) laboratories recently prepared a series of 36Cl/Cl isotopic ratio AMS standards by an eight-step serial gravimetric dilution scheme. Of the resulting nine solutions, only the latter six could be assayed by AMS to confirm the gravimetric dilution factors. This paper provides the results of relative radioactivity measurements on the first four solutions to verify the first three dilution factors. The fourth solution was the only dilution capable of being directly measured by both AMS and radionuclidic metrology of 36Cl, and therefore its assay by radioactivity counting was deemed of considerable importance. Assays were performed by 4πβ− liquid scintillation (LS) counting of gravimetric aliquots of the solutions, with confirmatory measurements by 2πβ− gas-flow proportional counting of gravimetrically-prepared solid sources. The radioactivity measurements on the fourth solution were complex and difficult because of the conflicting combination of a low activity concentration (0.036 Bq · g−1) and high salt content (146 mg NaCl per g of solution). These conditions necessitated independent studies of the 36Cl LS efficiency as a function of NaCl loading in the LS cocktails and of the feasibility of LS counting of precipitated samples, both of which are also reported here. The results of the radioactivity measurements confirmed the dilution factors for the first three solutions to absolute differences of about 1%, and that for the fourth solution to about 1% to 2%. The overall uncertainties for these verification measurements, at a relative three standard deviation uncertainty interval, were of comparable magnitude, i.e., in the range of ±1% to ±2% for the first three solutions and roughly ±3% for the fourth solution.