Craig M. Marianno

Predicting Concrete Roadway Contribution to Gamma-Ray Background in Radiation Portal Monitor Systems

Abstract The collapse of the Soviet Union ushered in an era of interest in the security of the radiological and nuclear material holdings of the Russian Federation and other countries of the Former Soviet Union. Additionally, the increasing sophistication of international criminal and terrorist organizations highlighted the need to secure these materials and prevent them from being smuggled from their point of origin and across international boundaries. To combat the growing threat of radiological and nuclear smuggling, radiation portal monitors (RPMs) are deployed at ports of entry (POEs) around the world to passively detect gamma and neutron radiation signatures from cargo and pedestrian traffic. In some locations, RPMs are reporting abnormally high gamma-ray background count rates, a situation that has been attributed, in part, to the building materials surrounding the RPMs. The primary objective of this work was to determine the impact of different types of concrete on the gamma-ray background readings in a particular RPM. Secondary objectives include developing an adaptable model to estimate the gamma-ray background contribution from any composition of concrete in any RPM configuration and determining the elemental composition of different concrete samples through neutron activation analysis (NAA) techniques. The specific activities of 40K and isotopes from the 238U and 232Th decay series were determined with a high-purity germanium detector and computer-generated calibration files. Through NAA, 34 elemental compositions were determined for six concrete samples from three different parent slabs. The total weight percentages determined were 84% to 100% of the total mass of the samples. The Monte Carlo N-Particle (MCNP) transport code was used to simulate the RPM response to the different concrete slabs. The MCNP model was validated by comparing actual and simulated detector responses to 137Cs check sources of varying strengths. For all validation cases, the MCNP estimates were 6% to 16% less than the value obtained from the actual RPM data. This work shows that it is possible to estimate the gamma-ray response of an RPM to the underlying concrete roadway. Knowing the amount of this contribution will allow RPM customers to choose suitable foundation materials before installation and accurately set alarm thresholds. This could ultimately increase the ability of RPMs to detect radiation at POEs, thereby increasing the probability of a seizure of smuggled radiological and nuclear materials.

Predicting instrument detection efficiency when scanning point and small area radiation sources.

Abstract— Accurate quantification of radionuclides detected during a scanning survey relies on an appropriately determined scan efficiency calibration factor (SECF). Traditionally, instrument efficiency is determined with a stationary instrument and a fixed source geometry. However, as is often the case, the instrument is used in a scanning mode where the source to instrument geometry is dynamic during the observation interval. Procedures were developed to determine the SECF for a point source (“hot particle”) and a 10 × 10 cm source passing under the centerline of a 12.7 × 7.62 cm NaI(Tl) detector. The procedures were first tested to determine the SECF from a series of static point source measurements using Monte Carlo N-Particle code. These point static efficiency values were then used to predict the SECF for scan speeds ranging from 10 cm s−1 to 80 cm s−1 with a simulated instrument set to collect integrated counts for 1 s. The Monte Carlo N-Particle code was then used to directly determine the SECF by simulating a scan of a point source and 10 × 10 cm area source for scan speeds ranging from 10 cm s−1 to 80 cm s−1. Comparison with Monte Carlo N-Particle scan simulation showed the accuracy of the SECF prediction procedures to be within ±5% for both point and area sources. Experimental results further showed the procedures developed to predict the actual SECF for a point and 10 × 10 cm source to be accurate to within ±10%. Besides the obvious application to determine an SECF for a given scan speed, this method can be used to determine the maximum detector or source velocity for a desired minimum detectable activity. These procedures are effective and can likely be extended to determine an instrument specific SECF for a range of source sizes, scan speeds, and instrument observation intervals.

Neutron activation analysis of concrete for cross-border nuclear security

The dissolution of the Soviet Union coupled with the growing sophistication of international terror organizations has brought about a desire to ensure that a sound infrastructure exists to interdict smuggled nuclear material prior to leaving its country of origin. To combat the threat of nuclear trafficking, radiation portal monitors (RPMs) are deployed around the world to intercept illicit material while in transit by passively detecting gamma and neutron radiation. Portal monitors in some locations have reported abnormally high background counts. The higher background data has been attributed, in part, to the naturally occurring radioactive materials (NORM) in the concrete surrounding the portal monitors. Higher background increases the minimum detectable activity (MDA) and can ultimately lead to more material passing through the RPMs undetected. This work employed two different neutron activation analysis (NAA) methods for the purpose of developing a process to characterize the concrete surrounding the RPMs. Thermal neutron instrumental NAA (INAA) and fast NAA (FNAA) were conducted on six samples from three different composition concrete slabs. Comparator standards and quality control materials were used to help ensure that the methods were both precise and accurate. The combination of INAA and FNAA accounted for 84–100% of the total elemental composition of the samples. Knowing the composition of the concrete will allow RPM customers to choose suitable materials prior to installation, thereby increasing the ability of the monitors to detect radiological and nuclear materials.

An innovative technique in scanning land areas with a multi-FIDLER system.

Remediation can be a long and tedious effort. One possible step in this process is the scanning of land to locate elevated areas of radiological contamination. By adapting existing global positioning technology with radiation detection systems, this process can be significantly accelerated. The Field Instrument for Detecting Low Energy Radiation (FIDLER) was used in conjunction with a Global Positioning System (GPS) and Trimble data logger. With this system two different land areas were scanned using two different scanning methods. In the first method, three FIDLERs were attached to a baby jogger and were used to scan a 20-acre site devoid of vegetation. The second technique involved individuals carrying the instruments over a 15-acre site that contained vegetation. Here the FIDLERs were waved in front of the workers in 50-cm arcs. In all cases, radiological and position data were collected by the data loggers. Using these results, accurate maps were generated for each site clearly illustrating areas and spots of elevated activity. By employing this technique over 250,000 data points pertaining to position and count rate were used to map nearly 40 acres of land in under 3 wk.

Reconstructing the direction of reactor antineutrinos via electron scattering in Gd-doped water Cherenkov detectors

Abstract The potential of elastic antineutrino-electron scattering in a Gd-doped water Cherenkov detector to determine the direction of a nuclear reactor antineutrino flux was investigated using the recently proposed WATCHMAN antineutrino experiment as a baseline model. The expected scattering rate was determined assuming a 13-km standoff from a 3.758-GWt light water nuclear reactor and the detector response was modeled using a Geant4-based simulation package. Background was estimated via independent simulations and by scaling published measurements from similar detectors. Background contributions were estimated for solar neutrinos, misidentified reactor-based inverse beta decay interactions, cosmogenic radionuclides, water-borne radon, and gamma rays from the photomultiplier tubes (PMTs), detector walls, and surrounding rock. We show that with the use of low background PMTs and sufficient fiducialization, water-borne radon and cosmogenic radionuclides pose the largest threats to sensitivity. Directional sensitivity was then analyzed as a function of radon contamination, detector depth, and detector size. The results provide a list of experimental conditions that, if satisfied in practice, would enable antineutrino directional reconstruction at 3 σ significance in large Gd-doped water Cherenkov detectors with greater than 10-km standoff from a nuclear reactor.

Background characterization of an ultra-low background liquid scintillation counter

The Ultra-Low Background Liquid Scintillation Counter developed by Pacific Northwest National Laboratory will expand the application of liquid scintillation counting by enabling lower detection limits and smaller sample volumes. By reducing the overall count rate of the background environment approximately 2 orders of magnitude below that of commercially available systems, backgrounds on the order of tens of counts per day over an energy range of ~3-3600keV can be realized. Initial test results of the ULB LSC show promising results for ultra-low background detection with liquid scintillation counting.

Development of a customized radiation monitor for livestock screening.

AbstractThe monitoring and decontamination of livestock has been an emerging topic in emergency response planning in recent years. Under the National Response Framework, the U.S. Department of Agriculture is tasked with providing support to the states during a radiological incident for the “assessment, control, and decontamination of contaminated animals, including companion animals, livestock, poultry, and wildlife.” While there are currently no protocols in place on a national level for coordinated animal response, working groups have been developing a command structure and task force procedures, and some states have issued their own guidelines. A customized Bovine Screening Portal was manufactured and tested at Texas A&M University to investigate the operational capabilities in detecting, identifying, and localizing external contamination on livestock. An array of six sodium iodide detectors attached to power-over-Ethernet Multi-Channel Analyzers was used to collect time-stamped count rates, and spectral data were collected as a heifer was led past the detector panel. A 1.85 × 105 Bq 137Cs source was placed in four locations on a heifer, which was led through a cattle chute adjacent to the detector panel. The trials were repeated walking the heifer through a walkway with detectors hung on cattle pens lining a walkway. The Bovine Screening Portal observed increased count rates (>10&sgr;) from the 1.85 × 105 Bq 137Cs source in live time. The identification capabilities with the intuitive software interface of the BSP are consistent with the requirements of a detection system for radiological emergency management of livestock.

Developing a Methodology for Determination of Elemental Composition of Shielding Materials.

AbstractRadiation transport simulation models can provide estimations of radiation effects such as detector response and detection capabilities. The objective of this research was to develop a methodology for quick, efficient, and effective determination of the composition of shielding materials to be used in radiation transport models. A C++ code, MatFit, was developed that used the concept of densitometry and the iterative method developed for the Spectrum Analysis by Neutron Detectors II (SAND II) computer program to estimate the elemental composition of shielding materials. These results were compared to previous neutron activation analysis (NAA) on the same samples. It was determined that densitometry provided an elemental approximation that yielded an attenuation rate within 10% of that found through NAA but requires much fewer resources, as well as less time. From this research, it is recommended that the developed method and C++ program be used when constructing models for detector response.

Calculation of Canine Dose Rate Conversion Factors for Photons and Electrons

Abstract Urban search and rescue (USAR) dogs are valuable members of their teams and play key roles in performing successful missions. A pair of dogs can do the work of dozens of people, the dogs are able to quickly sniff around collapsed structures and zip through constricted hallways with far greater accuracy than their plodding human counterparts. While in contaminated areas, their human counterparts are afforded the benefit of personal protective equipment (PPE) to keep exposures to chemical, biological and radiological substances to a minimum; USAR dogs, on the other hand, are not. In an effort to allow USAR dogs to be used to their full potential, PPE is often not worn as it inhibits their ability to move in and around obstacles to use their strong senses of smell and hearing. In addition, these animals may snag or be snagged on debris or structures, which may require rescue of the animal. In a collaborative effort between Texas A&M University’s Department of Nuclear Engineering and the College of Veterinary Medicine, researchers are attempting to estimate the extent of the radiation doses received by these valuable team members during missions where radioactive contamination is present. Currently there are no dose rate conversion factors for USAR dogs, and those that are available are calculated at a height of 1 m. To address this issue, a more suitable height of 40 cm was chosen, and dose conversion factors were calculated for monoenergetic photon sources ranging from 15 keV to 15 MeV and for monoenergetic electron sources ranging from 10 keV to 10 MeV. The radioactivity is assumed to be uniformly distributed on the surface of the ground. Forty centimeters was chosen as the height of interest for the three breeds FEMA prefers as USAR dogs. These dose conversion factors will permit dose estimates to be made, allowing these animals to do their jobs successfully while keeping their radiation doses as low as possible.

Radionuclide Selection for Emergency Response Exercise at Disaster City® Using Unsealed Radioactive Contamination

Abstract The Department of Nuclear Engineering at Texas A&M University currently supports exercises at Disaster City®, a mock community used for emergency response training that features full-scale, collapsible structures designed to simulate various levels of disaster and wreckage. Emergency response exercises can be enhanced by using unsealed radioactive sources to simulate a more realistic response environment following an incident involving the dispersion of radioactive material. Limited exercises are performed worldwide using unsealed radioactive sources, and most of that information is not publicly available. This research compiles the publicly available information along with additional information acquired through discussion with experts and presents the process for selection of a short-lived radionuclide for use at Disaster City®. The historically-used radionuclides were 18F, 99mTc, 82Br, and 140La. These radionuclides were considered for the Disaster City® exercise, as well as other short-lived radionuclides commonly used or capable of being produced at Texas A&M. The selection process described in this paper identified seven radionuclides that could be used in an unsealed contamination exercise at Disaster City®. Radiopharmaceuticals 99mTc and 18F are suitable and available for purchase from nearby vendors. In addition, the Texas A&M Nuclear Science Center TRIGA reactor could be used to produce 24Na, 56Mn, 64Cu, 82Br, and 140La via thermal neutron activation.