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Since 1998, there have been improvements in the capability to detect atmospheric radioxenon in the International Monitoring System operated by the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization. The upgrades have resulted in next-generation versions of the radioxenon systems. This paper explores radioxenon data analysis improvements beyond the original radioxenon beta–gamma analysis equations that were formulated in 2000. Additionally, it provides recommendations to further improve analysis and refine the equations. The areas of improvement are described in terms of equations, physical detectors, and field-testing. These recommendations are provided with the intention of improving accuracy and precision of radioxenon measurements. [ABSTRACT FROM AUTHOR]

A spectroscopic stack monitoring system for the measurement of noble gasses discharged from medical isotope production facility and nuclear power plant stacks has been designed and a prototype constructed. The prototype is based on a Marinelli beaker style HPGe measurement operating in a continuous acquisition mode. Continuous acquisition is accomplished with novel software and hardware which allows for unattended acquisition, analysis, and storage of data over multiple workflow definitions. As a direct result of the multiple averaging times and the use of the transistor reset preamplifier, the dynamic range of the system covers nearly 8 orders of magnitude. [ABSTRACT FROM AUTHOR]

Quantification of low-activity noble gases in air is typically accomplished through separation of the noble gas from air followed by radiometric assay. This work is aimed at quantification of radioactive noble gas in air without extraction. A high pressure aluminum Marinelli counting vessel was designed and fabricated that can be placed on a coaxial high purity germanium detector for gamma counting. Characterization of the performance of this Marinelli using MCNP modeling, large excesses of activity, and low-activity noble gas in air is discussed. Minimum detectable concentrations achieved during a 24 h count are: 5, 10, 50, and 1 Bq/m for Xe, Xe, Xe, and Xe, respectively. [ABSTRACT FROM AUTHOR]

The production of radioargon through the irradiation of CaO was performed in an in-core facility within the The University of Texas at Austin MARK II TRIGA reactor. The major radioargon isotope produced was Ar via the Ca(n,α)Ar reaction pathway. The CaO powder was vacuumed sealed in a quartz ampoule. The sample was irradiated in a Cd-lined Al alloy canister for 2 h at 500 kW. After the irradiation, the sample was counted using an HPGe detector five times with increasing count times. Ar, K, K, and Ca were detected in the spectra. The induced activities of Ar, Ar, Ar, K, K, and Ca were calculated using a 63-group energy-dependent neutron flux determined utilizing a neutron energy flux profile calculated from a MCNPX model of the TRIGA reactor core. The production ratios generated from the model allowed for the estimation of induced Ar and Ar activities through the measured induced activities of Ar, K, K, and Ca. [ABSTRACT FROM AUTHOR]

It is well known that radon is present in relatively high concentrations below the surface of the Earth due to natural decay of uranium and thorium. However, less information is available on the background levels of other isotopes such as Xe and Xe produced via spontaneous fission of either manmade or naturally occurring elements. The background concentrations of radioxenon in the subsurface are important to understand because these isotopes potentially can be used to confirm violations of the comprehensive nuclear-test-ban treaty during an on-site inspection. Recently, Pacific Northwest National Laboratory measured radioxenon concentrations from the subsurface at the Nevada Nuclear Security Site (NNSS-formerly known as the Nevada Test Site) to determine whether xenon isotope background levels could be detected from spontaneous fission of naturally occurring uranium or legacy Pu as a result of historic nuclear testing. In this paper, we discuss the results of those measurements and review the sources of xenon background that must be taken into account during OSI noble gas measurements. [ABSTRACT FROM AUTHOR]

Performing accurate and verifiable measurements is often the most challenging goal for any radiation detector and is especially challenging for the radio-xenon detectors deployed by the International Monitoring System (IMS) of the Preparatory Commission of the Comprehensive Test Ban Treaty Organization (CTBTO). Often the accuracy of the measurement is directly tied to how well the detector is calibrated, in both energy and efficiency. Standard methods often rely on using certified sealed sources to determine the absolute efficiency. Similarly, efforts to calibrate the absolute efficiency of radioactive gas cell detectors utilize a number of methodologies which allow adequate calibration but are time consuming and prone to a host of difficulties to determine uncertainties (McIntyre et al, J Radioanal Nucl Chem 282(3):755-759, ; Anderson et al, Stat Probab Lett 77(88):769-773, ). Utilizing methods developed in the 1960s for absolute measurements of activity with beta-gamma detector systems it has become clear that it is possible to achieve higher precision results that are consistent across a range of isotopes and activities (National Council on Radiation Protection and Measurement, A handbook of radioactivity measurements procedure NCPR report, ). Even more compelling is the ease with which this process can be used on routine samples to determine the total activity present in the detector. Additionally, recent advances in the generation of isotopically pure radio-xenon samples of Xe, Xe, and Xe allow these measurement techniques to achieve much better results than have previously been possible when using mixed isotopic radio-xenon sources (Haas et al, J Radioanal Nucl Chem 282(3):677-680, ). This paper will discuss the beta/gamma absolute detection efficiency techniques of direct measurement of the efficiencies and the extrapolation method and compare the results using modeled and measured pure sources of Xe and Xe. [ABSTRACT FROM AUTHOR]

Detection of anthropogenic noble gas isotopes in the atmosphere is an important indication that a below ground nuclear-test has taken place. Diffusion plays a critical role in the transport of these gases through the geological media to the surface where they can be detected. Better techniques are need with which to study the diffusion of noble gases through porous systems. Here we demonstrate the suitability of using prompt gamma activation analysis to measure the time dependent concentration of argon as a result of its diffusion through a porous medium that is saturated with nitrogen at atmospheric pressure. The experiments were conducted in a 1 m long tube, 10 cm diameter, and packed with fine SiO sand. Prompt gamma activation analysis was used to measure the concentration of argon within the experimental system as a function of time. [ABSTRACT FROM AUTHOR]

Using particulate and noble gas raw data analysed from Comprehensive Nuclear Test-Ban-Treaty (CTBT) monitoring sites, Canadian National Surveillance networks and atmospheric transport modelling, it is possible to associate some of the main events in the Fukushima accident timeline with observations, and perturbations in isotopic ratios in Japan, through the Pacific and into North America. Additional sources identified during the accident period will be commented upon in the context of CTBT treaty verification. [ABSTRACT FROM AUTHOR]

Radioargon has been identified as a useful nuclide for verifying compliance with the Comprehensive Nuclear-Test-Ban Treaty. Use of Ar to identify a nuclear explosion requires quantification of contributions to the Ar background at a potential measurement site. A method of estimating Ar release activities using isotopes of radioxenon and radioargon has been developed in this paper. Numerical solutions to the system of equations describing air-activation in a reactor were used to determine ratios of release activities for Xe/Xe, Xe/Xe, and Ar /Ar as function of irradiation time and off-gas residence time prior to measurement and release. Published radioactive noble gas effluent data for the High Flux Isotope Reactor, HFIR (ORNL) from the year 1996 to 2010 were compiled as a test data set to predict the Ar release on a yearly basis. An average Ar release rate of 1.86 × 10 Bq per year was calculated. The estimated release rate was used as a source term for atmospheric transport to run a test case for Ar release over a typical HFIR operation cycle. Results showed that ground-level concentrations of Ar did not exceed the minimum detectable concentration for a Ar field measurement system beyond the immediate vicinity of the release point. [ABSTRACT FROM AUTHOR]

A large volume, in-core gas irradiation technique was developed at The University of Texas at Austin MARK II TRIGA reactor to produce a sample of Ar with an activity above 1 mBq. The method requires a large volume, 1.4 L, of natural Ar gas (99.6003 % Ar) at about 1 atm and three 12 h irradiation periods. The production of Ar requires a double capture to be produced from the stable Ar isotope. This method produced 940 kBq of Ar, 3.08 MBq Ar, 114 GBq Ar, and 0.311 Bq Ar at the end of the final irradiation period. [ABSTRACT FROM AUTHOR]

A method was developed and implemented that calculates energy versus channel calibrations. This method utilizes a Cs spectrum acquired in β-γ coincidence. Both the γ singles and the β-γ coincident spectrum are utilized. The γ singles spectrum is utilized to calculate the γ detector energy versus resolution function. The Compton line in the β-γ coincidence is then used to calculate the β detector energy versus resolution function. Currently a linear regression ( y = mx + b) is utilized to fit the data. However, higher order polynomials may easily be implemented if desired. [ABSTRACT FROM AUTHOR]

To support interpretation of observed atmospheric krypton radioisotopes, a database of krypton radioisotope in the primary coolant of CANDU reactors has been established. This database is comprised of 40,000 records of high-quality 89Kr, 87Kr, 88Kr and 85mKr analyses. Records from the database were retrieved by a specifically designed data-mining module and subjected to further analysis. Results from the analysis were subsequently used to study isotopic ratios of observed krypton radioisotopes in the CANDU reactor primary coolant. These studies provided practical information on the characterization of CANDU reactor krypton radioisotope, which can potentially be used to discriminate between reactor effluent and fuel reprocessing for nuclear safeguard 85Kr monitoring applications (Kalinowski et al., J Environ Radioact 73:203, 2004). The study also has some potential application to Fissile material cut-off treaty. [ABSTRACT FROM AUTHOR]

Radioxenon concentration data collected at International Noble Gas Experiment (INGE) monitoring sites in the Northern Hemisphere are demonstrably impacted by emissions from medical isotope (MI) production facilities at Chalk River (CRL), Ontario and Fleurus, Belgium [Saey, J Environ Radioact 100(5):396–406, 2009]. Temporary cessation at these European MI facilities in the latter half of 2008 allowed an opportunity to assess the relative impact of distant MI facilities at INGE monitoring stations. In particular, the concentration distributions at the measurement sites and calculated sensitivities to the putative emission locations through atmospheric transport modelling (ATM) of meteorological Source Receptor Sensitivity (SRS) computations were used to study MI impacts. [ABSTRACT FROM AUTHOR]

Following the claimed nuclear test in the Democratic People’s Republic of Korea (DPRK) on October 9, 2006, and a reported seismic event, a mobile system for sampling of atmospheric xenon was transported to the Republic of South Korea (ROK) in an attempt to detect possible emissions of radioxenon in the region from a presumed test. Five samples were collected in the ROK during October 11–14, 2006 near the ROK–DPRK border, and thereafter transported to the Swedish Defense Research Agency (FOI) in Stockholm, Sweden, for analysis. Following the initial measurements, an automatic radioxenon sampling and analysis system was installed at the same location in the ROK, and measurements on the ambient atmospheric radioxenon background in the region were performed during November 2006 to February 2007. The measured radioxenon concentrations strongly indicate that the explosion in October 9, 2006 was a nuclear test. The conclusion is further strengthened by atmospheric transport models. Radioactive xenon measurement was the only independent confirmation that the supposed test was in fact a nuclear explosion and not a conventional (chemical) explosive. [ABSTRACT FROM AUTHOR]