Search

With a half-life of 10.7 years, the noble gas radioisotope 85Kr is perfectly suited as a tracer to date ice and water that formed during the past half century. Furthermore, due to its inhomogeneous input into the atmosphere, it is a useful tool to investigate atmospheric circulation and back-trajectory analysis. The data presented here represent a comprehensive time series of atmospheric 85Kr activity concentrations in ground level air that can be used to model northern and southern hemispheric input functions, which is essential to apply 85Kr as a dating tracer. The collection comprises 11 datasets from 4 monitoring stations in the northern and 7 monitoring stations in the southern hemisphere, respectively. In total, it contains about 8000 measurements performed over the past 60 years, making it the largest published 85Kr record.

For almost half a century weekly samples for the measurement of krypton-85 (85Kr) activity concentrations in surface air have been collected by the Bundesamt fur Strahlenschutz (BfS), Germany. Sampling started at Freiburg (230m asl) in 1973, Mt Schauinsland (1205m asl) in 1976 and Mt Jungfraujoch in Switzerland (3454 asl) in 1990. Distinct maxima in the time series of atmospheric 85Kr activity concentration are caused by emissions from nuclear reprocessing plants in Europe, mainly the La Hague, France, and Sellafield, UK, reprocessing plants. Between 1970 and 1990 peak activity concentrations measured in winter along the Rhine Rift in Freiburg are often higher than at Mt Schauinsland, due to emissions from the operating pilot reprocessing plant in Karlsruhe - approximately 130 km to the north - and large-scale inversions that inhibit exchange of air masses within the Rhine Rift with those at higher altitudes. From the early 1990s onwards, after the shut-down of the pilot plant, differences between Freiburg and Schauinsland are much smaller. Activity concentrations measured at Jungfraujoch are generally lower and close to baseline levels, due to its location in the free troposphere. Weekly baseline and average 85Kr activity concentration in the atmosphere in Central Europe were modelled from almost 12,000 individual measurements at 11 stations. The baseline and average have continuously increased, interrupted by a relatively stable period between 2009 and the end of 2014 with a baseline activity concentration of about 1.39 Bq/m3. Depending on the geographical location and hydrological conditions, the modelled baseline or average 85Kr activity concentration time series can be used as input functions for the dating of young groundwater.

In July 2015, the currently only active monitoring station for atmospheric 85Kr measurements in the southern hemisphere went operational at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Adelaide, Australia. Here, this new data is presented and combined with measurements from historic monitoring stations, to generate a85Kr input function for the southern hemisphere which is crucial for the application of 85Kr as a dating tracer for water and ice. After a linear increase in atmospheric 85Kr concentrations between 1980 and 2005, concentrations stabilized yielding mean 85Kr activity concentration during the Adelaide monitoring period of 1.3 ± 0.15 Bq/m³ air with slight variations indicating seasonal effects. Data from three northern hemispheric monitoring stations Schauinsland, Freiburg and Jungfraujoch of the German Federal Office for Radiation Protection (BfS), located in Central Europe are used to calculate an interhemispheric exchange time of 1.25 ± 0.24 years, using a simple box model approach. Furthermore, it is investigated whether a southern hemispheric 85Kr input function can be calculated from the baseline of the northern hemispheric data set. A comparison between the calculated and the fitted input function shows that analytical techniques can just resolve the concentration differences, emphasising the need of southern hemispheric monitoring stations for 85Kr. Analysing the decay-corrected input function and taking the current detection limit of low-level counting and Atom Trap Trace Analysis of 0.05 Bq/m³ air, a maximum apparent 85Kr tracer age of 40 years can be determined in the southern hemisphere. Finally, the 85Kr measurements are used to derive global 85Kr emission rates which are found to be in good agreement with published emissions from nuclear reprocessing plants.

Atmospheric 85Kr and 133Xe activity concentrations were determined from weekly air samples collected at Sapporo, Akita and Chiba, Japan, throughout 2011. The results demonstrated that the Fukushima Dai-ichi Nuclear Power Plant accident in early March 2011 resulted in high 133Xe activity concentrations as well as elevated levels of 85Kr activity; there was a striking increase in the concentrations of both isotopes over the week running from 14 to 22 March as the radioactive plume released from the plant was captured. At Chiba, following the accident, the 85Kr activity concentration increased from 1.38 to 17.7 Bq/m3, while the 133Xe levels increased from below the minimum detectable concentration (MDC ≤ 1.9 × 10−3 Bq/m3) to 1.3 × 103 Bq/m3. Conversely, at Sapporo and Akita, high 85Kr activity concentrations were not observed, due to differences in air transportation mechanisms based on wind directions. Duplicate samples were collected at Chiba to allow the simultaneous analyses of 85Kr and 133Xe at the Japa...

Krypton-85 activity concentrations in surface air have been measured at Darwin, which is located in northern Australia and is influenced by seasonal monsoonal activity. Measurements between August 2007 and May 2010 covered three wet seasons. The mean activity concentration of krypton-85 measured during this period was 1.31 ± 0.02 Bq m −3 . A linear model fitted to the average monthly data, using month and monsoon as predictors, shows that krypton-85 activity concentration measured during the sampling period has declined by 0.01 Bq m −3 per year. Although there is no statistically significant difference in mean activity concentration of krypton-85 between wet and dry season, the model implies that activity concentration is higher by about 0.015 Bq m −3 during months influenced by the monsoon when a north westerly flow prevails. Backward dispersion runs using the Lagrangian particle dispersion model Hysplit4 highlight possible source regions during an active monsoon located deep in the northern hemisphere, and include reprocessing facilities in Japan and India. However, the contribution of these facilities to krypton-85 activity concentrations in Darwin would be less than 0.003 Bq m −3 .

none 13 si The Fukushima-labeled air mass arrival, and later the cesium-134 (134Cs), cesium-137 (137Cs) and particulate iodine-131 (hereafter noted 131Ip) maximum levels were registered in Europe at different dates depending on the location. Most of those data were obtained at low-altitude sampling areas. Here, we compare the airborne levels registered at different high-altitude European locations (from 850 m to about 3500 m). The integrated 137Cs activity concentration was not uniform with regard to the altitude even after a long travel time/distance from Japan. Moreover, the relation of integrated 137Cs vs. altitude showed a linear decrease up to an altitude of about 3000 m. A similar trend was noticed for 131Ip (particulate fraction) while it increased above 3000 m. Comparison with 7Be activity concentration showed that, as far as the high altitude location is concerned, the 137Cs and 134Cs maximum concentrations corresponded to the 7Be maximum, suggesting downdraft movements from high tropospheric or stratospheric layers to be responsible for 137,134Cs increase and peak values. This was also confirmed by high potential vorticity and low relative humidity registered during the peak values. Masson, Olivier; Bieringer, Jacqueline; Brattich, Erika; Dalheimer, Axel; Estier, Sybille; Penev, Ilia; Ringer, Wolfgang; Schlosser, Clemens; Steinkopff, Thomas; Steinmann, Philipp; Tositti, Laura; Beek, Pieter Van; Vismes-Ott, Anne de Masson, Olivier; Bieringer, Jacqueline; Brattich, Erika; Dalheimer, Axel; Estier, Sybille; Penev, Ilia; Ringer, Wolfgang; Schlosser, Clemens; Steinkopff, Thomas; Steinmann, Philipp; Tositti, Laura; Beek, Pieter Van; Vismes-Ott, Anne de

A European-wide 222Radon/222Radon progeny comparison study has been conducted in order to determine correction factors that could be applied to existing atmospheric 222Radon data sets for quantitative use of this tracer in atmospheric transport model validation. Two compact and easy-to-transport Heidelberg Radon Monitors (HRM) were moved around to run for at least one month at each of the nine European measurement stations that were included in the comparison. Linear regressions between parallel data sets were calculated, yielding correction factors relative to the HRM ranging from 0.68 to 1.45. A calibration bias between ANSTO (Australian Nuclear Science and Technology Organisation) two-filter radon monitors and the HRM of ANSTO/HRM = 1.11 ± 0.05 was found. For continental stations, which use one-filter systems, preliminary 214Po/222Rn disequilibrium values were estimated to lie between 0.8 at mountain stations (e.g. Schauinsland) and 0.9 at non-mountain sites for sampling heights around 20 to 30 m above ground level. Respective corrections need to be applied to obtain a consistent European 222Radon data set for further applications.

Proportional counters and a β-γ coincidence system and their performance characteristics are described, with emphasis on internal and external quality controls. Typical limits of detection (LD) are 8mBqm-3 for 85Kr and 4mBqm-3 for 133Xe for the proportional counters, while for similar xenon volumes the LD for 133Xe in the β-γ system is approximately 4 times lower. Results of comparative analyses agree above the limit of quantification. Xenon-133 levels in southern Germany are presently at or below the LD of the proportional counters, but above the LD of the β-γ system, which is now routinely used for analysis of environmental samples.

International audience; The International Monitoring System (IMS) is part of the verification regime for the Comprehensive Nuclear-Test-Ban-Treaty Organization (CTBTO). At entry-into-force, half of the 80 radionuclide stations will be able to measure concentrations of several radioactive xenon isotopes produced in nuclear explosions, and then the full network may be populated with xenon monitoring afterward. An understanding of natural and man-made radionuclide backgrounds can be used in accordance with the provisions of the treaty (such as event screening criteria in Annex 2 to the Protocol of the Treaty) for the effective implementation of the verification regime.Fission-based production of 99Mo for medical purposes also generates nuisance radioxenon isotopes that are usually vented to the atmosphere. One of the ways to account for the effect emissions from medical isotope production has on radionuclide samples from the IMS is to use stack monitoring data, if they are available, and atmospheric transport modeling. Recently, individuals from seven nations participated in a challenge exercise that used atmospheric transport modeling to predict the time-history of 133Xe concentration measurements at the IMS radionuclide station in Germany using stack monitoring data from a medical isotope production facility in Belgium. Participants received only stack monitoring data and used the atmospheric transport model and meteorological data of their choice.Some of the models predicted the highest measured concentrations quite well. A model comparison rank and ensemble analysis suggests that combining multiple models may provide more accurate predicted concentrations than any single model. None of the submissions based only on the stack monitoring data predicted the small measured concentrations very well. Modeling of sources by other nuclear facilities with smaller releases than medical isotope production facilities may be important in understanding how to discriminate those releases from releases from a nuclear explosion. © 2016.

The Fukushima-labeled air mass arrival, and later the cesium-134 (

Radioxenon emissions of the TRIGA Mark II research reactor in Vienna were investigated with respect to a possible impact on the verification of the Comprehensive Nuclear Test-Ban-Treaty. Using the Swedish Automatic Unit for Noble Gas Acquisition (SAUNA II), five radioxenon isotopes 125Xe, 131mXe, 133mXe, 133Xe and 135Xe were detected, of which 125Xe is solely produced by neutron capture in stable atmospheric 124Xe and hence acts as an indicator for neutron activation processes. The other nuclides are produced in both fission and neutron capture reactions. The detected activity concentrations ranged from 0.0010 to 190 Bq/m³. The source of the radioxenon is not yet fully clarified, but it could be micro-cracks in the fuel cladding, fission of 235U contaminations on the outside of the fuel elements or neutron activation of atmospheric Xe. Neutron deficient 125Xe with its highly complex decay scheme was seen for the first time in a SAUNA system. In many experiments the activity ratios of the radioxenon nuclides carry the signature of nuclear explosions, if 131mXe is omitted. Only if 131mXe is included into the calculations of the isotopic activity ratios, the majority of the measurements revealed a “civil” signature (typical for a NPP). A significant contribution of the TRIGA Vienna to the global or European radioxenon inventory can be excluded. Due to the very low activities, the emissions are far below any concern for human health.

The general characterisation of the global radioxenon background is of interest for the verification of the Comprehensive Nuclear-Test-Ban Treaty. Since the major background sources are only a few isotope production facilities, their source term has an emphasized influence on the worldwide monitoring process of radioxenon. In this work, two different datasets of source terms are applied through atmospheric transport modelling, to estimate the concentration at two radioxenon detection stations in Germany and Sweden. One dataset relies on estimated average annual emissions; the other includes monthly resolved measurements from an isotope production facility in Fleurus, Belgium. The quality of the estimations is then validated by comparing them to the radioxenon concentrations that have been sampled at two monitoring stations over the course of 1 year.

Medical isotope production facilities (MIPF) have recently been identified to emit the major part of the environmental radioxenon measured at many globally distributed monitoring sites deployed to strengthen the radionuclide component of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification regime. Efforts to raise a global radioxenon emission inventory revealed that the yearly global total emission from MIPF’s is around 15 times higher than the total radioxenon emission from nuclear power plants (NPP's). Given that situation, from mid 2008 until early 2009 two out of the ordinary hemisphere-specific events occured: 1) In the Northern hemisphere, a joint temporary suspension of operations of the three largest MIPF's made it possible to quantify the effects of the emissions related to NPP’s. The average activity concentrations of 133 Xe measured at a monitoring station close to Freiburg, Germany, went down significantly from 4.5 ± 0.5 mBq/m 3 to 1.1 ± 0.1 mBq/m 3 and in Stockholm, Sweden, from 2.0 ± 0.4 mBq/m 3 to 1.05 ± 0.15 mBq/m 3 . 2) In the Southern hemisphere the only radioxenon-emitting MIPF in Australia started up test production in late November 2008. During eight test runs, up to 6.2 ± 0.2 mBq/m 3 of 133 Xe was measured at the station in Melbourne, 700 km south-west from the facility, where no radioxenon had been observed before, originating from the isotopic production process. This paper clearly confirms the hypothesis that medical isotope production facility are at present the major emitters of radioxenon to the atmosphere. Suspension of operations of these facilities indicates the scale of their normal contribution to the European radioxenon background, which decreased two to four fold. This also gives a unique opportunity to detect and investigate the influence of other local and long distance sources on the radioxenon background. Finally the opposing effect was studied: the contribution of the start-up of a renewed radiopharmaceutical facility to the build up of a radioxenon background across Australia and the Southern hemisphere.

Parallel monitoring of 222Rn and its short-lived progeny (218Po and 214Pb) were carried out from November 2007 to April 2008 close to the top of the Schauinsland mountain, partly covered with forest, in South-West Germany. Samples were aspired from the same location at 2.5 m above ground level. We measured 222Rn with a dual flow loop, two-filter detector and its short-lived progeny with a one-filter detector. A reference sector for events, facing a steep valley and dominated by pasture, was used to minimize differences between 222Rn and progeny-derived 222Rn activity concentrations. In the two major wind sectors covered by forest to a distance between 60 m and 80 m towards the station progeny-derived 222Rn activity concentration was on average equal to 87% (without precipitation) and 74% (with precipitation) of 222Rn activity concentration. The observations show that most of the time both detector types follow the same pattern. Still, there is no single disequilibrium factor that could be used to exactly transform short-lived progeny to 222Rn activity concentration under all meteorological conditions.

Atmospheric measurement of radioactive xenon isotopes (radioxenon) plays a key role in remote monitoring of nuclear explosions, since it has a high capability to capture radioactive debris for a wide range of explosion scenarios. It is therefore a powerful tool in providing evidence for nuclear testing, and is one of the key components of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The reliability of this method is largely based on a well-developed measurement technology. In the 1990s, with the prospect of the build-up of a monitoring network for the CTBT, new development of radioxenon equipment started. This article summarizes the physical and technical principles upon which the radioxenon technology is based and the advances the technology has undergone during the last 10 years. In contrast to previously used equipment, which was manually operated, the new generation of radioxenon monitoring equipment is designed for automated and continuous operation in remote field locations. Also the analytical capabilities of the equipment were strongly enhanced. Minimum detectable concentrations of the recently developed systems are well below 1 mBq/m3 for the key nuclide 133Xe for sampling periods between 8 and 24 h. All the systems described here are also able to separately measure with low detection limits the radioxenon isotopes 131mXe, 133mXe and 135Xe, which are also relevant for the detection of nuclear tests. The equipment has been extensively tested during recent years by operation in a laboratory environment and in field locations, by performing comparison measurements with laboratory type equipment and by parallel operation. These tests demonstrate that the equipment has reached a sufficiently high technical standard for deployment in the global CTBT verification regime.

Activity concentration data from ambient radioxenon measurements in ground level air, which were carried out in Europe in the framework of the International Noble Gas Experiment (INGE) in support of the development and build-up of a radioxenon monitoring network for the Comprehensive Nuclear-Test-Ban Treaty verification regime are presented and discussed. Six measurement stations provided data from 5 years of measurements performed between 2003 and 2008: Longyearbyen (Spitsbergen, Norway), Stockholm (Sweden), Dubna (Russian Federation), Schauinsland Mountain (Germany), Bruyeres-le-Châtel and Marseille (both France). The noble gas systems used within the INGE are designed to continuously measure low concentrations of the four radioxenon isotopes which are most relevant for detection of nuclear explosions: 131mXe, 133mXe, 133Xe and 135Xe with a time resolution less than or equal to 24 h and a minimum detectable concentration of 133Xe less than 1 mBq/m3. This European cluster of six stations is particularly interesting because it is highly influenced by a high density of nuclear power reactors and some radiopharmaceutical production facilities. The activity concentrations at the European INGE stations are studied to characterise the influence of civilian releases, to be able to distinguish them from possible nuclear explosions. It was found that the mean activity concentration of the most frequently detected isotope, 133Xe, was 5–20 mBq/m3 within Central Europe where most nuclear installations are situated (Bruyeres-le-Châtel and Schauinsland), 1.4–2.4 mBq/m3 just outside that region (Stockholm, Dubna and Marseille) and 0.2 mBq/m3 in the remote polar station of Spitsbergen. No seasonal trends could be observed from the data. Two interesting events have been examined and their source regions have been identified using atmospheric backtracking methods that deploy Lagrangian particle dispersion modelling and inversion techniques. The results are consistent with known releases of a radiopharmaceutical facility.

Cosmogenic radionuclides in the one-million-year half-life range offer unique possibilities for age determinations in geophysics. In measurements where the radioactive decay is being utilized as a clock, uncertainties in age determinations may be reduced if the ratio of two radioisotopes with different half-lives can be used as a chronometer. In this work we investigate the atomic ratio of atmospheric 26Al (t1/2 = 0.717 Ma) to 10Be (t1/2 = 1.386 Ma) measured with accelerator mass spectrometry (AMS), and its potential as a chronometer for dating old ice. The 26Al/10Be ratio decreases with an effective half-life of t1/2(26Al/10Be) = 1.49 Ma. For its application as a chronometer, the atmospheric 26Al/10Be ratio has to be well characterized. However, the properties of atmospheric 26Al have been understood only poorly so far. At the VERA AMS facility of the University of Vienna, a first systematic study of the global variations of the 26Al/10Be ratio in the atmosphere and in surface firn has been carried out, and pilot measurements of the 26Al/10Be ratio in deep Antarctic ice have been performed. Our results indicate that this ratio is globally constant to within 5% in the atmosphere and in surface firn with a mean value of 1.89 × 10− 3. The data also suggest that non-atmospheric sources of 26Al, such as extraterrestrial, in situ produced or re-suspended 26Al, do not contribute significantly to the observed 26Al/10Be ratio. In addition, atmospheric mixing seems to exert only a minor influence. In a first application of the method, 26Al/10Be ratios were measured in chips collected in connection with the drilling of the lowest part of an ice core (2250 to 2760 m) in Dronning Maud Land, Antarctica. Surprisingly, variable 26Al/10Be ratios ranging between 0.5 and up to 2 times the atmospheric ratio were found at different locations in this deep ice core. While the cause for the ratios higher than atmospheric remains unexplained so far, the ratios lower than atmospheric may be caused by radioactive decay, allowing a first dating attempt using the 26Al/10Be ratio. Thus, at an ice depth of 2760 m an approximate date of (6.7 ± 2.6) × 105 years was established.

Since February 1992, measurements of atmospheric CO2 at 200 m above the ground have been taken from a meteorological tower (lat 36.1°N, long 140.1°E, 25 m a.s.l.) in Tsukuba, central Japan. We have examined seasonal/long-term variations in atmospheric CO2, based on atmospheric 85Kr, a noble gas with well-known source and sink terms, monitored continuously at weekly intervals in Tsukuba since May 1995. During the annual cycle, the daily mean values of atmospheric CO2 in the afternoons (1300-1600 JST) showed maximum in late April, except in 2002, and minimum in late August or early September. The seasonal variations in atmospheric 85Kr, which is low in summer and high in winter, were caused by the seasonal variations in the large-scale atmospheric circulation, and latitudinal distribution of atmospheric 85Kr. Compared with seasonal variations in atmospheric 85Kr, the draw-down (DD) and buildup (BU) for atmospheric CO2 occurred about 1 week and 3 weeks later, respectively. The peak-to-trough amplitude of de-trended seasonal variations in atmospheric CO2 concentrations ranged from 11 to 14 ppm. A decrease in the seasonal CO2 minimum occurred with a decrease in the 85Kr concentration, showing the effect of air mass transport from different origins. Unlike the minimum, the maximum CO2 did not vary as expected from the air mass transport. The daily mean values of atmospheric CO2 increased at an average rate of 2.0 ppm yr−1, with a range from −0.5 to 4 ppm yr−1. While both CO2 and 85Kr are emitted into the atmosphere, due to energy consumption, the growth rate of atmospheric CO2 showed a pattern different from that of atmospheric 85Kr (0.03 Bq m−3 yr−1).

This paper gives the yearly 85 Kr emissions of all known reprocessing facilities, which are the main sources of 85 Kr in the atmosphere since 1945, for the years 1945 until 2000. According to this inventory 10,600 PBq (Peta = 10 15 ) of 85 Kr have been globally emitted from the year 1945 until the end of 2000. The global atmospheric inventory at the end of the year 2000 amounts to 4800 PBq. These emissions have been incorporated into the ECHAM4 atmospheric general circulation model as point sources. Monthly mean model results are compared with measurements made at different locations and times. The influence of each source on the measured concentrations at various locations is studied. The calculated concentrations are found to give reasonably good agreement with the observations, indicating that the emission inventory is realistic. Although, at all northern hemispheric observation sites the model tends to slightly overestimate the concentrations. A possible reason for this overestimation can be found in model features (coarse resolution in time and space). The most prominent discrepancy that is consistently repeated at all northern hemispheric stations occurs in the early 1990s. This could most likely be related to an overestimate of sources. Possibly, the Russian emissions declined earlier than assumed in the current database. Another discrepancy between observations and simulations indicating an incompleteness of the release data is found at some southern hemispheric sites. The variability of their observations could only be explained by regional sources. However, several spikes occur after 1992 when no reprocessing facility is known to be in operation in the southern hemisphere. Production of isotopes for radiopharmaceuticals like technetium-99m from highly enriched uranium is the most likely explanation.

Equipment for measurement of radioactive noble gases for the international monitoring system (IMS) of the comprehensive nuclear test-ban treaty (CTBT) was developed. An equipment test is being carried out by the Provisional Technical Secretariat of the CTBTO. The developed systems are assessed for their suitability for the IMS. The requirements for the noble gas monitoring network of the CTBT are reported. The different technologies used in the developed systems are described. The phases of the test and results are reported.

Atmospheric 8 5 Kr/Annual growth rate/Nuclear fuel reprocessing plant/Emission/Inventory Atmospheric 8 5 Kr concentrations have been continuously monitored since 1995 at the Meteorological Research Institute (MRI) in Tsukuba, Japan. They have also been observed once a year at several stations over the Japanese islands since 1995. The annual growth rate of the background atmospheric 8 5 Kr concentrations in Tsukuba was 0.03 Bq.m - 3 .yr - 1 during 1996-2001. The atmospheric 8 5 Kr concentrations at several stations over Japan were within the range of the annual variations in Tsukuba. However, higher and lower 8 5 Kr concentrations in early winter, compared with those in Tsukuba (36.1°N, 140.1°E), occurred in Sapporo (43.1°N, 141.3°E) and Ishigaki (24.3°N, 124.2°E), respectively. The reason for this is that Sapporo is covered by a continental air mass, some from European sources, whereas Ishigaki is still covered by a subtropical air mass. The Northern Hemispheric background 8 5 Kr concentrations from 1994 to 2001 was calculated from the 8 5 Kr inventory and the release rate of 8 5 Kr from the nuclear fuel reprocessing plants in Europe. Calculated 8 5 Kr concentrations in surface air were in good agreement with annual average observed values at the MRI, Tsukuba. The global atmospheric inventory of 8 5 Kr in December 2001 was also estimated to be approximately 5 EBq by using observed data in Tsukuba.

After the accident in the Japanese Fukushima Dai-ichi nuclear power plant in March 2011 large amounts of radioactivity were released and distributed in the atmosphere. Among them were also radioactive noble gas isotopes which can be used as tracers to test global atmospheric circulation models. This work presents unique measurements of the radionuclide $^{133}$Xe from Fukushima in the upper troposphere above Germany. The measurements involve air sampling in a research jet aircraft followed by chromatographic xenon extraction and ultra-low background gas counting with miniaturized proportional counters. With this technique a detection limit of the order of 100 $^{133}$Xe atoms in litre-scale air samples (corresponding to about 100 mBq/m$^3$) is achievable. Our results provide proof that the $^{133}$Xe-rich ground level air layer from Fukushima was lifted up to the tropopause and distributed hemispherically. Moreover, comparisons with ground level air measurements indicate that the arrival of the radioactive plume at high altitude over Germany occurred several days before the ground level plume., 8 pages, 5 figures

Radioactive emissions into the atmosphere from the damaged reactors of the Fukushima Dai-ichi nuclear power plant (NPP) started on March 12th, 2011. Among the various radionuclides released, iodine-131 ( 131I) and cesium isotopes ( 137Cs and 134Cs) were transported across the Pacific toward the North American continent and reached Europe despite dispersion and washout along the route of the contaminated air masses. In Europe, the first signs of the releases were detected 7 days later while the first peak of activity level was observed between March 28th and March 30th. Time variations over a 20-day period and spatial variations across more than 150 sampling locations in Europe made it possible to characterize the contaminated air masses. After the Chernobyl accident, only a few measurements of the gaseous 131I fraction were conducted compared to the number of measurements for the particulate fraction. Several studies had already pointed out the importance of the gaseous 131I and the large underestimation of the total 131I airborne activity level, and subsequent calculations of inhalation dose, if neglected. The measurements made across Europe following the releases from the Fukushima NPP reactors have provided a significant amount of new data on the ratio of the gaseous 131I fraction to total 131I, both on a spatial scale and its temporal variation. It can be pointed out that during the Fukushima event, the 134Cs to 137Cs ratio proved to be different from that observed after the Chernobyl accident. The data set provided in this paper is the most comprehensive survey of the main relevant airborne radionuclides from the Fukushima reactors, measured across Europe. A rough estimate of the total 131I inventory that has passed over Europe during this period was \textless1% of the released amount. According to the measurements, airborne activity levels remain of no concern for public health in Europe. © 2011 American Chemical Society.

The Federal Office for Radiation Protection (BfS) performs trace analysis measurements in both the frameworks of the German Integrated Measuring and Information system as well as of the International Monitoring System for verification of the Comprehensive Nuclear-Test-Ban Treaty. Therefore, different kinds of measurements of aerosol bound radionuclides as well as of radioactive noble gases in the atmosphere are performed. BfS as coordinating laboratory for trace analysis is responsible for the quality control. A quality assurance programme was set up with German institutions and expanded to European laboratories. The existing quality assurance programme of the Comprehensive Nuclear-Test-Ban Treaty Organisation for measurements of aerosol bound radionuclides will be extended for noble gas measurements. Applied methods, achieved measurement results and the different kinds of quality assurance are presented and discussed.

Data from three years of operation of a low-level aerosol sampler and analyzer (RASA) at Schauinsland monitoring station are reported. The system is part of the International Monitoring System (IMS) for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The fully automatic system is capable to measure aerosol borne gamma emitters with high sensitivity and routinely quantifies 7Be and 212Pb. The system had a high level of data availability of 90% within the reporting period. A daily screening process rendered 66 tentative identifications of verification relevant radionuclides since the system entered IMS operation in February 2004. Two of these were real events and associated to a plausible source. The remaining 64 cases can consistently be explained by detector background and statistical phenomena. Inter-comparison with data from a weekly sampler operated at the same station shows instabilities of the calibration during the test phase and a good agreement since certification of the system.

Environmental sample analysis is not a new verification method. It has been applied ever since the first nuclear weapons were produced and tested and related national technical means played a major role in verifying compliance with the Partial Test Bean Treaty of 1963. However, scientific progresses in measurement technologies and source location methods as well as major verification applications for nuclear arms control (UNSCOM/UNMOVIC since 1990 and CTBT since 1996) in recent years have brought significant progress. New opportunities are being explored with regard to wide-area environmental sampling according to the NPT Additional Protocol (model agreement of 1997). Further proposals include the to-be-negotiated Fissile Materials Cut-off Treaty (Shannon Mandate of 1995) as well as bilateral or regional agreements on cooperative environmental monitoring as confidence building measures.

Radioactive xenon monitoring is one of the main technologies used for the detection of underground nuclear explosions. Precise and reliable measurements of (131m)Xe, (133g)Xe, (133m)Xe, and (135g)Xe are required as part of the International Monitoring System for compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). For the first time, simultaneous testing of four highly sensitive and automated fieldable radioxenon measurement systems has been performed and compared to established laboratory techniques. In addition to an intercomparison of radioxenon monitoring equipment of different design, this paper also presents a set of more than 2000 measurements of activity concentrations of radioactive xenon made in the city of Freiburg, Germany in 2000. The intercomparison experiment showed, that the results from the newly developed systems agree with each other and the equipment fulfills the fundamental requirements for their use in the verification regime of the CTBT. For 24-h measurements, concentrations as low as 0.1 mBqm(-3) were measured for atmospheric samples ranging in size from 10 to 80 m(3). The (133)Xe activity concentrations detected in the ambient air ranged from below 1 mBqm(-3) to above 100 mBqm(-3).

The use of the xenon isotopes for detection of nuclear explosions is of great interest for monitoring compliance with the comprehensive nuclear-test-ban treaty (CTBT). Recently, the automated radioxenon sampler-analyzer (ARSA) was tested at the Institute for Atmospheric Radioactivity (IAR) in Freiburg, Germany to ascertain its use for the CTBT by comparing its results to laboratory-based analyses, determining its detection sensitivity and analyzing its results in light of historical xenon isotope levels and known reactor operations in the area. Xe-133 was detected nearly every day throughout the test at activity concentrations ranging between approximately 0.1 mBq/m3 to as high as 120 mBq/m3. Xe-133m and 135Xe were also detected occasionally during the test at concentrations of less than 1 to a few mBq/m3.