Argon-37 is an important environmental signature of an underground nuclear explosion. Producing and quantifying low-level 37Ar standards is an important step in the development of sensitive field ...measurement instruments for use during an On-Site Inspection, a key provision of the Comprehensive Nuclear-Test-Ban Treaty. This paper describes progress at Pacific Northwest National Laboratory (PNNL) in the development of a process to generate and quantify low-level 37Ar standard material, which can then be used to calibrate sensitive field systems at activities consistent with soil background levels. The 37Ar used for our work was generated using a laboratory-scale, high-energy neutron source to irradiate powdered samples of calcium carbonate. Small aliquots of 37Ar were then extracted from the head space of the irradiated samples. The specific activity of the head space samples, mixed with P10 (90% stable argon:10% methane by mole fraction) count gas, is then derived using the accepted Length-Compensated Internal-Source Proportional Counting method. Due to the low activity of the samples, a set of three Ultra-Low Background Proportional-Counters designed and fabricated at PNNL from radio-pure electroformed copper was used to make the measurements in PNNL’s shallow underground counting laboratory. Very low background levels (<10 counts/day) have been observed in the spectral region near the 37Ar emission feature at 2.8 keV. Two separate samples from the same irradiation were measured. The first sample was counted for 12 days beginning 28 days after irradiation, the second sample was counted for 24 days beginning 70 days after irradiation (the half-life of 37Ar is 35.0 days). Both sets of measurements were analyzed and yielded very similar results for the starting activity (~0.1 Bq) and activity concentration (0.15 mBq/ccSTP argon) after P10 count gas was added. A detailed uncertainty model was developed based on the ISO Guide to the Expression of Uncertainty in Measurement. This paper presents a discussion of the measurement analysis, along with assumptions and uncertainty estimates.
Low-background lead for radiation measurement shielding is often assayed for
Pb to ensure acceptable backgrounds. Samples of lead assayed with a germanium spectrometer calibrated for ...bremsstrahlung-based assay of
Pb provide a view into the
Pb content of commercial lead in the U.S. (other than stockpiled Doe Run lead). Results suggest that the loss of lead smelting in the U.S. has eliminated the traditional supply of "low background" lead (~30Bqkg
), and indicate current commercial supplies contain roughly an order of magnitude higher
Pb levels.
Copper is one of few elements that have no long-lived radioisotopes and which can be electrodeposited to ultra-high levels of purity. Experiments probing neutrino properties and searching for direct ...evidence of dark matter require ultra-clean copper, containing the smallest possible quantities of radioactive contaminants. Important to the production of such copper is establishing the location and dispersion of contamination within the bulk material. Co-deposition of contaminants during copper electrodeposition and its relationship to nucleation and growth processes were investigated using scanning electron microscopy (SEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and secondary ionization mass spectrometry (SIMS).
One IGEX 76Ge double-beta decay detector is currently operating in the Canfranc Underground Laboratory in a search for dark matter WIMPs, through the Ge nuclear recoil produced by the WIMP elastic ...scattering. A new exclusion plot, σ(m), has been derived for WIMP-nucleon spin-independent interactions. To obtain this result, 40 days of data from the IGEX detector (energy threshold Ethr∼4 keV), recently collected, have been analyzed. These data improve the exclusion limits derived from all the other ionization germanium detectors in the mass region from 20 to 200 GeV, where a WIMP supposedly responsible for the annual modulation effect reported by the DAMA experiment would be located. The new IGEX exclusion contour enters, by the first time, the DAMA region by using only raw data, with no background discrimination, and excludes its upper left part. It is also shown that with a moderate improvement of the detector performances, the DAMA region could be fully explored.
A pulse shape analysis technique was implemented to determine the electron mobility /spl mu//sub e/ and the electron mobility lifetime product /spl mu//sub e//spl tau//sub e/ in cadmium zinc ...telluride detectors (CZT). The digital gamma finder (DGF-4C) a single-width CAMAC module produced by X-Ray Instrumentation Associates (XIA), was used to extract pulse height, pulse shape, and signal rise time information. Data analyses using the extracted information allowed measuring the /spl mu//sub e/ and /spl mu//sub e//spl tau//sub e/ in selected CZT samples. An almost linear relationship was observed for the signal rise time as a function of the inverse bias. This observed linear relationship was the basis for determination of /spl mu//sub e/ using a simple linear fit. The measured signal amplitude was also used to determine /spl mu//sub e//spl tau//sub e/ using the Hecht formulation. Repeated measurements confirmed the consistency of the method in determining /spl mu//sub e/ and /spl mu//sub e//spl tau//sub e/.
Many measurements in the physical sciences can be cast as counting experiments, where the number of occurrences of a physical phenomenon informs the prevalence of the phenomenon’s source. Often, ...detection of the physical phenomenon (termed signal) is difficult to distinguish from naturally occurring phenomena (termed background). In this case, the discrimination of signal events from background can be performed using classifiers, and they may range from simple, threshold-based classifiers to sophisticated neural networks. These classifiers are often trained and validated to obtain optimal accuracy, however we show that the optimal accuracy classifier does not generally coincide with a classifier that provides the lowest detection limit, nor the lowest quantification uncertainty. We present a derivation of the detection limit and quantification uncertainty in the classifier-based counting experiment case. We also present a novel abstention mechanism to minimize the detection limit or quantification uncertainty a posteriori. We illustrate the method on two data sets from the physical sciences, discriminating Ar-37 and Ar-39 radioactive decay from non-radioactive events in a gas proportional counter, and discriminating neutrons from photons in an inorganic scintillator and report results therefrom.
The ability to conduct automated trace radionuclide analysis at or near the sample collection point would provide a valuable tool for emergency response, environmental monitoring, and verification of ...treaties and agreements. Pacific Northwest National Laboratory is developing systems for this purpose based on dual gamma-ray spectrometers, e.g., NaI(TI) or HPGe, combined with thin organic scintillator sensors to detect light charged particles. Translating the coincident signatures recorded by these systems, which include betagamma,gammagamma, and betagammagamma, into the concentration of detectable radionuclides in the sample requires generalized multicoincidence analysis tools. The development and validation of the Coincidence Lookup Library, which currently contains the probabilities of single and coincidence signatures from more than 420 isotopes, is described. Also discussed is a method to calculate the probability of observing a coincidence signature which incorporates true coincidence summing effects. These effects are particularly important for high-geometric-efficiency detection systems. Finally, a process for verifying the integrated analysis software package is demonstrated using GEANT 4 simulations of the prototype detector systems
This work addresses the energy spectrum correction due to increased charge carrier collection times in larger HPGe spectrometers. The energy of the radiation interaction is expected to be ...proportional to the total collected charge. This is increasingly not true with larger HPGe spectrometers. Some charge is lost as the total charge travels from the interaction location to the collection electrode. This path dependent loss of charge results in decreased energy resolution. In HPGe spectrometers, this process is characterized by the charge carrier lifetime constant and is given as an exponential function of the charge carrier collection time divided by this constant. Thus large detectors can experience exponential decrease in energy resolution as charge carrier collection time increases. We studied the effect of charge carrier lifetime on energy resolution for a p-type point contact HPGe spectrometers using pulse shape analysis. We present a method using the rise time to correct for the charge carrier lifetime on a pulse by pulse basis for a given HPGe spectrometer.
Development of a low-level 37Ar calibration standard Williams, R.M.; Aalseth, C.E.; Bowyer, T.W. ...
Applied radiation and isotopes,
March 2016, 2016-03-00, 2016-03-01, Letnik:
109, Številka:
C
Journal Article
Recenzirano
Odprti dostop
Argon-37 is an environmental signature of an underground nuclear explosion. Producing and quantifying low-level 37Ar standards is an important step in the development of sensitive field measurement ...instruments. This paper describes progress at Pacific Northwest National Laboratory in developing a process to generate and quantify low-level 37Ar standards, which can be used to calibrate sensitive field systems at activities consistent with soil background levels. This paper presents a discussion of the measurement analysis, along with assumptions and uncertainty estimates.
•A process is described for producing Bq quantities of Ar-37 using D–T generator.•Length-compensated proportional counting is used to quantify the specific activity.•We discuss Ar-37 standards related to the Comprehensive Nuclear-Test Ban Treaty.•An uncertainty analysis, following the ISO GUM guidelines, is presented.
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