Tom R. Heimbigner

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.

Magnetic field characteristics of electric bed-heating devices.

Measurements of the flux density and spectra of magnetic fields (MFs) generated by several types of electric bed heaters (EBH) were made in order to characterize the MFs to which the fetus may be exposed in utero from the mothers use of these devices. Data on MPs were gathered from more than 1,300 in-home and laboratory spot measurements. In-home measurements taken at seven different positions 10 cm from the EBHs determined that the mean flux density at the estimated position of the fetus relative to the device was 0.45 microT (4.5 mG) for electric blankets and 0.20 microT (2.0 mG) for electrically heated water beds. A rate-of-change (RC) metric applied to the nighttime segment of 24 h EMDEX-C personal-dosimeter measurements, which were taken next to the bed of volunteers, yielded an approximate fourfold to sixfold higher value for electric blanket users compared to water-bed heater users. These same data records yielded an approximate twofold difference for the same measurements when evaluated by the time-weighted-average (TWA)MF exposure metric. Performance of exposure meters was checked against standard fields generated in the laboratory, and studies of sources of variance in the in-home measurement protocols were carried out. Spectral measurements showed that the EBHs measured produced no appreciable high-frequency MFs. Data gathered during this work will be used in interpreting results from a component of the California Pregnancy Outcome Study, which evaluates the use of EBHs as a possible risk factor in miscarriage.

Requirements for Xenon International

This document defines the requirements for the new Xenon International radioxenon system. The output of this project will be a Pacific Northwest National Laboratory (PNNL) developed prototype and a manufacturer-developed production prototype. The two prototypes are intended to be as close to matching as possible; this will be facilitated by overlapping development cycles and open communication between PNNL and the manufacturer.

Beta-gamma coincidence counting using an yttrium aluminum perovskit and bismuth germanate phoswich scintillator

Phoswich detectors (two scintillators attached to the same photomultiplier-tube) have been used in the past to measure either betas or gammas separately but were not used to measure beta-gamma coincidence signatures. These coincidence signatures are very important for the detection of many fission products and are exploited to detect four radioxenon isotopes using the automated radioxenon sampler/analyzer (ARSA). Previous PNNL work with a phoswich detector used a commercially available, thin disk of scintillating CaF/sub 2/(Eu) and a 2 thick NaI(Tl) crystal in a phoswich arrangement. Studies with this detector measured the beta-gamma coincidence signatures from /sup 133/Xe, /sup 214/Pb and /sup 214/Bi. This scintillator combination worked but was not a good match in scintillation light decay times, 940 ns for CaF/sub 2/(Eu) and 230 ns for NaI(Tl). Additionally, a 6-mm thick quartz window was placed between the NaI(Tl) and the CaF/sub 2/ to ensure a hermetic seal for the NaI(Tl) crystal . This dead layer significantly reduced the detection probability of the low energy X-rays and gammas that are part of the coincidence signatures for /sup 214/Pb, /sup 214/Bi and the radioxenons. Further research showed that Yttrium aluminum perovskit (YAP) and bismuth germanate (BGO) have very good scintillation light characteristics and no hermetic seal requirements. The 27-ns scintillation light decay time of YAP and the 300-ns decay time for BGO are a good match between fast and slow light output. The scintillation light output was measured using XIA/spl trade/ digital signal processing readout electronics, and the fast (YAP) and slow (BGO) light components allowed discrimination between the beta and gamma contributions of the radioactive decays. In this paper we discuss the experimental setup and results obtained with this new phoswich detector and the applications beyond radioxenon gas measurements. A companion paper using plastic scintillator and CsI(Na) has also shown very promising results.

Final Technical Report on Radioxenon Event Analysis

This is a final deliverable report for the Advanced Spectral Analysis for Radioxenon project with a focus on radioxenon event categorization.

Neural Network Based State of Health Diagnostics for an Automated Radioxenon Sampler/Analyzer

Artificial neural networks (ANNs) are used to determine the state-of-health (SOH) of the Automated Radioxenon Analyzer/Sampler (ARSA). ARSA is a gas collection and analysis system used for non-proliferation monitoring in detecting radioxenon released during nuclear tests. SOH diagnostics are important for automated, unmanned sensing systems so that remote detection and identification of problems can be made without onsite staff. Both recurrent and feed-forward ANNs are presented. The recurrent ANN is trained to predict sensor values based on current valve states, which control air flow, so that with only valve states the normal SOH sensor values can be predicted. Deviation between modeled value and actual is an indication of a potential problem. The feed-forward ANN acts as a nonlinear version of principal components analysis (PCA) and is trained to replicate the normal SOH sensor values. Because of ARSAs complexity, this nonlinear PCA is better able to capture the relationships among the sensors than standard linear PCA and is applicable to both sensor validation and recognizing off-normal operating conditions. Both models provide valuable information to detect impending malfunctions before they occur to avoid unscheduled shutdown. Finally, the ability of ANN methods to predict the system state is presented.

Beta-cell Assembly for the Quad Gas Sampling Detector

The beta-cells used in the beta-gamma detector have taken time to develop and to standardize the assembly of them. In making the assembly routine it is important to have step by step assembly instructions as well as a list of potential problems and their solutions. This document attempts to accomplish these goals.

Pressure Sensor Calibration using VIPA Hardware

The VIPA hardware uses a series of modules to control the system. One of the modules that the VIPA hardware uses is a 16-bit analog input module. The main purpose of this module is to read in a voltage. The inputs of these modules are connected directly to the voltage outputs of all the pressure sensors in the system. Because the sensors have different pressure and voltage output ranges, it is necessary to calibrate and scale the sensors so that the values make sense to the operator of the system.

Generation of Radixenon Isotopes

Pacific Northwest National Laboratory has developed an automated system for separating Xe from air and can detect the following radioxenon isotopes, 131mXe, 133mXe, 133Xe, and 135Xe. This report details the techniques used to generate the various radioxenon isotopes that are used for the calibration of the detector as well as other isotopes that have the potential to interfere with the fission produced radioxenon isotopes. Fission production is covered first using highly enriched uranium followed by a description and results from an experiment to produce radioxenon isotopes from neutron activation of ambient xenon.