Pacific Northwest National Laboratory (PNNL) staff developed the Radionuclide Aerosol Sampler Analyzer (RASA) for worldwide aerosol monitoring in the 1990s. Recently, researchers at PNNL and Creare, LLC, have investigated possibilities for how RASA could be improved, based on lessons learned from more than 15 years of continuous operation, including during the Fukushima Daiichi Nuclear Power Plant disaster. Key themes addressed in upgrade possibilities include having a modular approach to additional radionuclide measurements, optimizing the sampling/analyzing times to improve detection location capabilities, and reducing power consumption by using electrostatic collection versus classic filtration collection. These individual efforts have been made in a modular context that might constitute retrofits to the existing RASA, modular components that could improve a manual monitoring approach, or a completely new RASA. Substantial optimization of the detection and location capabilities of an aerosol network is possible and new missions could be addressed by including additional measurements.

Studies have revealed that plastic scintillators such as polyvinyl toluene and polystyrene can undergo environmentally related material damage ("fogging'') that adversely affects detection performance under certain conditions and histories. A significant decrease in sensitivity has been seen in some gamma-ray detectors as they age as a result of this damage. Performance degradation due to such damage is characterized by a signal change from the detector, which shifts to lower energy, and ultimately a reduction in the ability to detect gamma radiation. This degradation is due to the permeation of water into the plastic, which can then cause temporary fogging and permanent damage to the material. As an example, a 1-mm thick barrier of high-density polyethylene with an area of 1 m(2) would allow 5 g per year of water transmission at 100% relative humidity. Thus, significant amounts of water can penetrate plastics over time and provide the potential for damage to the plastic. Such damage to plastic scintillator can cause problems for radiation detection applications in uncontrolled environments. Mitigation approaches that have been proposed to prevent damage to plastic scintillator include encapsulation of the plastic scintillator to prevent water intrusion that leads to damage during cold cycles. It is concluded that an encapsulation material with a moisture vapor transmission rate on the order of 10(-4) g.m(-2).d(-1)or better is needed for protecting large pieces of plastic scintillator from fogging over years of use. This paper presents information on testing of bare and encapsulated plastic scintillator samples and on diagnostic approaches to measure the nature and progression of the fogging condition. It is shown that several encapsulation approaches fail to prevent water intrusion, while a couple methods can successfully encapsulate plastic and prevent water from penetrating the plastic and producing fogging.

AbstractA radioactive particulate release experiment to produce a near-field ground deposition representative of small-scale venting from an underground nuclear test was conducted to gather data in support of treaty capability development activities. For this experiment, a CO2‐driven “air cannon” was used to inject 140La, a radioisotope of lanthanum with 1.7‐d half-life and strong gamma-ray emissions, into the lowest levels of the atmosphere at ambient temperatures. Witness plates and air samplers were laid out in an irregular grid covering the area where the plume was anticipated to deposit based on climatological wind records. This experiment was performed at the Nevada National Security Site, where existing infrastructure, radiological procedures, and support personnel facilitated planning and execution of the work. A vehicle-mounted NaI(Tl) spectrometer and a polyvinyl toluene-based backpack instrument were used to survey the deposited plume. Hand-held instruments, including NaI(Tl) and lanthanum bromide scintillators and high purity germanium spectrometers, were used to take in situ measurements. Additionally, three soil sampling techniques were investigated and compared. The relative sensitivity and utility of sampling and survey methods are discussed in the context of on-site inspection.

We have developed an unattended sensor for detecting anomalous radiation sources. The system combines several technologies to reduce size and weight, increase battery lifetime, and improve decision-making capabilities. Sixteen Cs2LiYCl6:Ce (CLYC) scintillators allow for gamma-ray spectroscopy and neutron detection in the same volume. Low-power electronics for readout, high voltage bias, and digital processing reduce the total operating power to 1.7 W. Computationally efficient analysis algorithms perform spectral anomaly detection and isotope identification. When an alarm occurs, the system transmits alarm information over a cellular modem. In this paper, we describe the overall design of the unattended sensor, present characterization results, and compare the performance to stock NaI:Tl and He-3 detectors.

This paper describes some potential applications for UAVs (Unmanned Aerial Vehicles) in international nuclear safeguards. UAV missions can include indoor and outdoor operations including: 1) surveillance, which includes all types of sensors and imagers, 2) command and control augmentation (radio relays and real-time imagery used primarily to coordinate ground operations), and 3) physical sample collection and transport.

Atmospheric dispersion theory can be used to predict ground deposition of particulates downwind of a radionuclide release. This paper uses standard formulations found in Gaussian plume models to inform the design of an experimental release of short-lived radioactive particles into the atmosphere. Specifically, a source depletion algorithm is used to determine the optimum particle size and release height that maximizes the near-field deposition while minimizing both the required source activity and the fraction of activity lost to long-distance transport. The purpose of the release is to provide a realistic deposition pattern that might be observed downwind of a small-scale vent from an underground nuclear explosion. The deposition field will be used, in part, to study several techniques of gamma radiation survey and spectrometry that could be used by an On-Site Inspection team investigating such an event.

We have developed a wearable radiation sensor using Cs2LiYCl6:Ce (CLYC) for simultaneous gamma-ray and neutron detection. The system includes two ∅2.5×2.5cm3 crystals coupled to small, metal-body photomultiplier tubes. A custom, low-power electronics base digitizes the output signal at three time points and enables both pulse height and pulse shape discrimination of gamma rays and neutrons. The total counts, anomaly detection metrics, and identified isotopes are displayed on a small screen. Users may leave the device in unattended mode to collect long-dwell energy spectra. The system stores up to 18h of one-second data, including energy spectra, and may transfer the data to a remote computer via a wired or wireless connection. The prototype is 18×13×7.5cm3, weighs 1.3kg, not including the protective pouch, and runs on six AA alkaline batteries for 29h with the wireless link active, or 41h with the wireless link disabled. In this paper, we summarize the system design and present characterization results from the detector modules. The energy resolution is about 6.5% full width at half maximum at 662keV due to the small photomultiplier tube selected, and the linearity and pulse shape discrimination performance are very good.

We are developing a next-generation unattended sensor that can detect and identify radiation sources while operating on battery power for several weeks. The system achieves smaller size and weight over systems that use NaI:Tl and 3He detectors by using a relatively new scintillator, Cs2LiYCl6:Ce (CLYC). This material can detect both gamma rays and thermal neutrons, has best-case energy resolution under 4% full width at half maximum at 662 keV, and allows for particle discrimination by pulse amplitude as well as pulse shape. The overall design features an array of sixteen CLYC detectors, each read out by a photomultiplier tube and custom pulse processing electronics. A field-programmable gate array analyzes the energy spectra using computationally efficient algorithms for anomaly detection and basic isotope identification. In this paper, we report the results of a modeling study to optimize various parameters of the unattended sensor for best performance. Key parameters include the number and placement of detectors, dimensions and weight of the moderator, and location of the batteries. These results have guided the design of the proof-of-concept prototype.

The search for neutrinoless double beta decay in 76 Ge has driven the need for ultra-low background Ge detectors shielded by electroformed copper of ultra-high radiopurity (<0.1 μBq/kg). Although electrodeposition processes are almost sophisticated enough to produce copper of this purity, to date there are no methods sensitive enough to assay it. Inductively coupled plasma mass spectrometry (ICP/MS) can detect thorium and uranium at femtogram levels, however, this assay is hindered by high copper concentrations in the sample. Electrodeposition of copper samples removes copper from the solution while selectively concentrating thorium and uranium contaminants to be assayed by ICP/MS. Spiking 232 Th and 238 U into the plating bath simulates low purity copper and allows for the calculation of the electrochemical rejection rate of thorium and uranium in the electroplating system. This rejection value will help to model plating bath chemistry.

Spectrometers for the lowest-level radiometric measurements require materials of extreme radiopurity. Measurements of rare nuclear decays, e.g., neutrinoless double-beta decay, can require construction and shielding materials with bulk radiopurity reaching one micro-Becquerel per kilogram or less. When such extreme material purity is achieved, surface contamination, particularly solid daughters in the natural radon decay chains, can become the limiting background. High-purity copper is an important material for ultra-low-background spectrometers and thus is the focus of this work. A method for removing surface contamination at very low levels without attacking the bulk material is described. An assay method using a low-background proportional counter made of the material under examination is employed, and the preliminary result of achievable surface contamination levels is presented.

High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited on surfaces can represent the largest remaining background. To control these backgrounds, a copper cleaning chemistry has been developed. Designed to replace an effective, but overly aggressive concentrated nitric acid etch, this peroxide-based solution allows for a more controlled cleaning of surfaces. The acidified hydrogen peroxide solution will generally target the Cu+/Cu2+ species which are the predominant surface participants, leaving the bulk of copper metal intact. This preserves the critical tolerances of parts and eliminates significant waste disposal issues. Accompanying passivation chemistry has also been developed that protects copper surfaces from oxidation. Using a high-activity polonium surface spike, the most difficult-to-remove daughter isotope of radon, the performance of these methods are quantified.

Research investigating the application of pressure-cycled bubble chambers to fast neutron detection is described. Experiments with a Halon-filled chamber showed clear sensitivity to an AmBe neutron source and insensitivity to a (137)Cs gamma source. Bubble formation was documented using high-speed photography, and a ceramic piezo-electric transducer element registered the acoustic signature of bubble formation. In a second set of experiments, the bubble nucleation response of a Freon-134a chamber to an AmBe neutron source was documented with high-speed photography.

An online monitor has been designed, built, and tested that is capable of measuring the residual transuranic concentrations in processed high-level wastes with a detection limit of 370 Bq/ml (10 nCi/ml) in less than six hours. The monitor measures the (α,n) neutrons in the presence of gamma-ray fields up to 1 Sv/h (100 R/h). The optimum design was determined by Monte Carlo modeling and then tempered with practical engineering and cost considerations. A multiplicity counter is used in data acquisition to reject the large fraction of coincident and highly variable cosmic-ray-engendered background events and results in an S/N ratio ~1.

Radiation portal monitors are commonly used at international border crossings to detect illicit transport of radioactive material. Most monitors use plastic scintillators to detect gamma rays, but next-generation monitors may contain NaI(Tl). In order to directly compare the performance of the two types of detectors, a prototype NaI(Tl) monitor was tested at two international border crossings adjacent to a comparable plastic scintillator monitor. The NaI(Tl) monitor housed four large detectors, each 10.2 cm /spl times/ 10.2 cm /spl times/ 41 cm. The empirical data set from the two field tests contains approximately 3800 passages with known cargo loads for each vehicle. For a small subset of the vehicles, high purity germanium detector spectra were also collected. During the survey period several vehicles containing commercial products with naturally occurring radioactive material (NORM) passed through the monitor. Typical NORM cargo included pottery, large granite slabs, rock-based floor tiles, construction stone blocks, abrasive material, and fertilizer. Non-NORM sources included a large source of /sup 60/Co (200,000 GBq) and a shipment of uranium oxide, both items being legally transported. The information obtained during the tests provides a good empirical data set to compare the effectiveness of NaI(Tl) and plastic-scintillator portal monitors. The capability to be sensitive to illicit materials, but not alarm on NORM, is a key figure of merit for portal monitors.

A pilot plant is being designed at the U. S. Department of Energy's Savannah River Site (SRS) to demonstrate the removal of 90 Sr, 137 Cs, and transuranics from a high-level liquid waste stream prior to encapsulation in a Saltstone Facility. In-line monitors are required to determine the concentration of all radionuclides on this processed waste stream. Calibration standards containing 60 Co, 137 Cs, and 90 Sr were prepared and counted. Efficiency curves were generated. Strontium-90 is readily observable above the system background in the calibration standard count, and is observable at less than 3 nCi/ml in a mixed solution having the maximum allowable concentration of all other activities present in the proposed SRS effluent stream.

A pilot plant operation at the Savannah River Site will remove 90Sr, 137Cs, and transuranics from a high-level liquid waste stream prior to encapsulation in a Saltstone Facility. Monitors are required to determine the concentrations of all radionuclides, including transuranics, in real-time on this processed waste stream. A neutron counter used to measure the concentration of each actinide isotope present in the stream is described. The neutron counter assembly consists of nested annular layers of shielding, reflectors, detectors, and moderators. On-line, live-time system control and calibration is provided by a time-tagged neutron source embedded in the moderator assembly.

Discussions between Euratom and Pacific Northwest National Laboratory (PNNL) revealed a need for a neutron detection system that could measure the neutron profile down the entire length of a CASTOR in one measurement. The CASTORS (dry storage casks for spent fuel and vitrified wastes) are {approximately}6 m high and 2 x 2 m square in cross section. Neutron profiles of the CASTORS are desirable for both content identification and verification. Profile measurements have traditionally been done with {sup 3}He-based detectors {approximately}1 m high that scan the length of a CASTOR as they are lifted by a crane. Geometric reproducibility errors plague this type of measurement; hence, the ability to simultaneously measure the neutron profile over the entire length of the CASTOR became highly desirable. Use of the PNNL-developed neutron-sensitive glass fibers in the construction of a 6-m-high detector was proposed, and design and construction of the detector began.

An effective means of detecting airborne radioactive aerosol plumes has been developed and tested on aircraft platforms. The Real-Time Airborne Radiation Analysis and Collection (RTARAC) system was mounted in the wing pod of a Navy P-3 where it sampled 20 cubic meters of air per minute on each of eleven sequentially advanced filters. A 140% intrinsic gemanium detector counted radioactive particles collected on the 15 cm circular filters in real-time. Gamma-energy spectrum and near real-time analysis of the sample were displayed on a laptop computer.