K. H. Abel

Detection and analysis of xenon isotopes for the comprehensive nuclear-test-ban treaty international monitoring system.

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.

Measurements of ambient radioxenon levels using the automated radioxenon sampler/analyzer (ARSA)

The Pacific Northwest National Laboratory has developed an Automated Radioxenon Sampler/Analyzer (ARSA) in support of the Comprehensive Nuclear-Test-Ban-Treaty (CTBT) to measure four radioxenon isotopes: 131mXe, 133mXe, 133gXe, and 135gXe. This system uses a beta-gamma coincidence counting detector to produce two-dimensional plots of gamma-energy versus beta-energy. Betas and conversion electrons (CE) are detected in a cylindrical plastic scintillation cell and gamma and X-rays are detected in a surrounding NaI(Tl) scintillation detector. The ARSA has been field tested at several locations to measure the radioxenon concentrations. Most recently it has been deployed at the Institut für Atmosphärische Radioaktivität in Freiburg, Germany. During the first 4 months of 2000 the measured 133Xe oncentrations have varied between 0.0±0.1 and 110±10 mBq/m3 air. The longer lived 131mXe (T1/2 = 11.9 d) and short lived 135Xe (T1/2 = 9.1 h) have also been detected in small quantities, while 133mXe concentrations have been consistent with zero. Minimum detectable concentration (MDC) calculations for 133gXe fell well below the 1 mBq per standard-cubic-meter of air requirement adopted by the CTBT Preparatory Commission.1 A description of the radioxenon detector, the concentration and MDC calculations and preliminary results of the field test in Germany are presented.

Automated separation and measurement of radioxenon for the Comprehensive Test Ban Treaty

A fully automatic radioxenon sampler/analyzer (ARSA) has been developed and demonstrated for the collection and quantitative measurement of the four xenon radionuclides,131mXe(11.9 d),133mXe(2.2 d),133Xe(5.2 d), and135Xe(9.1 hr), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a Comprehensive Test Ban Treaty (CTBT). Activity ratios of these radionuclides permit source attribution. Xenon, continuously and automatically separated from the atmosphere, is automatically analyzed by electron-photon coincidence spectrometry providing a lower limit of detection of about 100 μBq/m3. The demonstrated detection limit is about 100 times better than achievable with reported laboratory-based procedures for the short-time collection intervals of interest.

Field testing of collection and measurement of radioxenon for the Comprehensive Test Ban Treaty

Pacific Northwest National Laboratory, with guidance and support from the U.S. Department of Energys NN-20 Comprehensive Test Ban Treaty (CTBT) Research and Development program, has developed and demonstrated a fully automatic sampler-analyzer (ARSA) for the collection and quantitative measurement of the four xenon radionuclides,131mXe (11.9 d),133mXe (2.19 d),133Xe (5.24 d), and135Xe (9.10 h), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a CTBT, and may have applications in stack monitoring and other areas where xenon radionuclides are present. The activity ratios between certain of these radionuclides permit discrimination between radioxenon originating from nuclear detonations and that from nuclear reactor operations, nuclear fuel reprocessing, or from medical isotope production and usage. With the ARSA system, xenon is continuously and automatically separated from the atmosphere at flow rates of about 100 lpm by sorption-bed techniques. Samples collected in 8 hours are automatically analyzed by electron-photon coincidence spectrometry to provide detection sensitivities as low as 100 μBq/m3 of air. This sensitivity is about 10-fold better than achieved with reported laboratory-based procedures1 for the short time collection intervals of interest. Gamma-ray energy spectra and gas analysis data are automatically collected.

Ambient 133Xe levels in the Northeast US

Measurements of 133Xe (τ12 = 5.2 days) atmospheric concentrations were performed during the fall of 1993 and throughout 1995 on ‘noble gas concentrates’ from the northeastern US. These samples were obtained from a commercial air-reduction plant in Allentown, Pennsylvania. Following Chromatographic purification of the xenon gas, the 133Xe activity was determined using a high-purity germanium gamma-ray spectrometer. The average 133Xe concentrations were in the range 1–3 mBq m−3, which is consistent with nuclear power plant noble gas releases in the region surrounding the sampling point, but approximately 50–100 times lower than those reported in Albany, NY approximately 300 km to the northeast from 1975 through 1984. The lower atmospheric concentrations are also consistent with the 100-fold reduction in radioxenon release from 25 nuclear reactors in that region. Only an upper limit could be established for the 135Xe level (τ12 = 9.1 h), which was about 0.03 of the 133Xe level. These background levels are of concern in monitoring for atmospheric radioxenons to assure compliance with a Comprehensive nuclear Test Ban Treaty (CTBT).

Selective, high-energy beta scintillation sensor for real-time, in situ characterization of uranium-238 and strontium-90

A novel scintillating-fiber sensor for detecting high-energy beta particles has been designed and built at the Pacific Northwest Laboratory to characterize238U and90Sr in surface soils. High-energy betas generate unique signals as they pass through multiple layers of scintillating fibers that make up the active region of the detector. Lower-energy beta particles, gamma rays, and cosmic-ray-generated particles comprise the majority of the background interferences. The resulting signals produced by these latter phenomena are effectively discriminated against due to the combination of the sensors multi-layer configuration and its interlayer coincidence/anti-coincidence circuitry.

Characterization of uranium contamination in surface soils

Abstract Traditional means of obtaining radionuclide concentrations in soils over large areas are often time-consuming, cumbersome, expensive, and potentially non-representative. In an attempt to develop improved systems and new methodologies for the rapid and economical characterization of large-scale uranium contamination, two disparate monitoring technologies were compared at a contaminated site within the Fernald facility near Cincinnati, Ohio, USA. The results of this preliminary study suggest that uncollimated in-situ γ spectrometry and high-energy β-scintillation sensing may represent viable alternatives to, and in many cases could mitigate the need for, the collection of myriad soil samples and subsequent laboratory analyses when characterizing large contaminated sites.

Characterization and calibration of a large area beta scintillation detector for determination of Sr-90

A large area beta scintillation detector has been developed which is currently capable of determining Sr-90/Y-90 contamination in surficial soils. The detector system employs scintillating fiber optic arrays, with active dimensions approximately 15 cm wide by 100 cm long, both ends of which are coupled to multiple photomultiplier tubes (PMTs). Electronic processing includes coincidence requirements to optimize sensitivity and selectivity for the 2.28 MeV (maximum) beta particle from Y-90. Low energy beta particles and gamma rays are discriminated against using double ended and multi-layer coincidence requirements. The detector system is personal-computer-software controlled and data restored in a format compatible with standard database software for ease of final data reduction. Experimental calibration studies have shown a linear response for Sr-90/Y-90 soil concentrations from 12 to over 500 pCi/g and a discrimination factor of 50 to 1 versus Cs-137.

Airborne radionuclides of concern and their measurement in monitoring a Comprehensive Test Ban Treaty

The U.S. Department of Energy (DOE) is conducting radioanalytical developmental programs with the goal of providing near real-time analysis technology for airborne signature radionuclides which are indicative of a nuclear weapons test in any of the earth’s environments. If a test were conducted in the atmosphere or above the atmosphere, then the full spectrum of fission and activation products, together with residues from the device would be dispersed in the atmosphere. However, if a nuclear test were conducted underground or underwater, the emission could range from a major to a very minor vent, and the material released would likely consist mainly of noble gas radionuclides and the radioiodines. Since many of the noble gases decay to form particulate radionuclides, these may serve as the more sensitive signatures. For example, Ba-140 is a daughter of Xe-140 (13.6 s), and Cs-137 is a daughter of Xe-137 (3.82 min). Both of these have been observed in large amounts relative to other fission products in dynamic venting of U.S. underground nuclear detonations.(1)

Ideas and concepts for diagnosis of performance and evaluation of data reliability based upon ARSA state-of-health (SOH) data

At the current time, the Pacific Northwest National Laboratory (PNNL) prototype for the Automated Radioxenon Sampler/Analyzer (ARSA) automatically transmits, on a daily basis, a subset of all state-of-health (SOH) data in an e-mail data file to a limited number of recipients. These variables represent what were considered the most critical physical parameters for the ARSAs operation at the beginning of the field demonstration in Freiburg, Germany. Operators at PNNL perform a daily review of the information in the data file for anomalous operational conditions as evidenced by sensor readings. The initial review is easily implemented by plotting the various sensor data versus time and looking for gross deviations in the periodicity of the variables compared to previous sample sensor data. After viewing the 24-hr graphical plots, if necessary, a review is conducted of the tabular data of specific sensor anomalies. In most cases, the experience has been that when there is an ARSA operational problem the data file will have multiple sensor readings that reflect some aspect of the problem.