Bruce D. Geelhood

Discrimination of naturally occurring radioactive material in plastic scintillator material

Plastic scintillator material is used in many applications for the detection of gamma rays from radioactive material, primarily due to the sensitivity per unit cost compared to other detection materials. However, the resolution and lack of full-energy peaks in the plastic scintillator material prohibits detailed spectroscopy. Therefore, other materials such as doped sodium iodide are used for spectroscopic applications. The limited spectroscopic information can, however, be exploited in plastic scintillator materials to provide some discrimination. The discrimination between man-made and naturally occurring sources would be useful in reducing alarm screening for radiation detection applications that target man-made sources. The results of applying the limited energy information from plastic scintillator material for radiation portal monitors are discussed.

Overview of portal monitoring at border crossings

The Bureau of Customs and Border Protection has the task of interdicting illicit radioactive material at ports of entry. Items of concern include radiation dispersal devices (RDD), nuclear warheads, and special nuclear material (SNM). The preferred survey method screens all vehicles in primary and diverts questionable vehicles to secondary. This requires high detection probability in primary while not overwhelming secondary with alarms, which could include naturally occurring radioactive material (NORM) found in acceptable cargo and radionuclides used in medical procedures. Sensitive alarm algorithms must accommodate the baseline depression observed whenever a vehicle enters the portal. Energy-based algorithms can effectively use the crude energy information available from a plastic scintillator to distinguish NORM from SNM. Whenever NORM cargo limits the alarm threshold, energy-based algorithms produce significantly better detection probabilities for small SNM sources than gross-count algorithms. Algorithms can be best evaluated using a large empirical data set to 1) calculate false alarm probabilities, 2) select sigma-level thresholds for operationally acceptable false alarm rates, and 3) determine detection probabilities for marginally detectable pseudo sources of SNM.

Comparison of plastic and NaI(Tl) scintillators for vehicle portal monitor applications

Experimental data and computer simulations are presented for gamma-ray detection by vehicle portal monitors for homeland security applications at international borders. The experiments and simulations use spectral processing of gamma rays from various sources (/sup 241/Am, /sup 57/Co, /sup 133/Ba, /sup 137/Cs, /sup 60/Co) and background to provide data for comparing plastic and NaI(Tl) detectors. The effects of gamma-ray scattering in cargo are also examined. Plastic scintillators are well suited for primary screening of gamma-ray sources because of their large size and low cost. Sodium iodide is preferable to plastic for applications of isotope identification based on gamma-ray spectrometry. Some applications may benefit from integrating features from both types of detectors.

Glass-fiber-based neutron detectors for high- and low-flux environments

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated lithium silicate scintillating fibers via a hot-downdraw process. These fibers typically have a operational transmission length (e-1 length) of greater than 2 meters. This permits the fabrication of devices which were not possible to consider. Scintillating fibers permit conformable devices, large-area devices, and extremely small devices; in addition, as the thermal-neutron sensitive elements in a fast neutron detection system, scintillating fibers can be dispersed within moderator, improving neutron economy, over that possible with commercially available 3He or BF3 proportional counters. These fibers can be used for national-security applications, in medical applications, in the nuclear-power industry, and for personnel protection at experimental facilities. Data are presented for devices based on single fibers and devices made up of ribbons containing many fibers under high-and low-flux conditions.

A field-deployable, aircraft-mounted sensor for the environmental survey of radionuclides

The Environmental Radionuclide Sensor System (ERSS)3 is an extremely sensitive sensor, which has been cooperatively developed by Pacific Northwest National Laboratory (PNNL) and Special Technologies Laboratory (STL) for environmental surveys of radionuclides. The ERSS sensors fit in an airborne pod and include twenty High-Purity Germanium (HPGe) detectors for the high-resolution measurement of gamma-ray emitting radionuclides, twenty-four3He detectors for possible neutron measurements, and two video cameras for visual correlation. These acrial HPGe sensors provide much better gamma-ray energy resolution than can be obtained with NaI(TI) detectors. The associated electronics fit into three racks. The system can be powered by the 28 V DC electrical supply of typical aircraft or 120 V AC. The data acquisition hardware is controlled by customized software and a real-time display is provided. Each gamma-ray event is time stamped and stored for later analysis. This paper will present the physical design, discuss the software used to control the system, and provide some examples of its use.

Composite Signatures of Nuclear and Non-Nuclear Technologies for Weapons Material and Component Measurement

Attribute measurement systems are being developed in support of arms-reduction negotiations to verify compliance with the disassembly of nuclear weapons and disposition of material. The currently demonstrated attribute measurement systems utilize nuclear radiation detection technologies. Alternative low-intrusion non-nuclear measurement techniques may offer access to relevant information, e.g. mass of an item, when combined with information from a nuclear radiation measurement. This document examines the application of low-intrusion non-nuclear methods in combination with nuclear methods for attribute measurement systems. Several specific combinations are evaluated.

Progress Report for the Advanced Large-Area Plastic Scintillator (ALPS) Project: FY 2003 Final

The DOE tasked PNNL to investigate possible technological avenues for substantially advancing the state-of-the-art in gamma detection via large-area plastic scintillators. This report describes progress on this project as of the conclusion of FY 2003. The primary focus of the report is on experimental tests conducted with a single large-area plastic scintillator outfitted with a variety of photomultiplier tube configurations. Measurements performed to date incude scintillator response under broad-area exposure to various point-like gamma sources, and light-output uniformity mappings obtained by varying the position of a collimated beta-source over the surface of the scintillator. Development of a Monte Carlo program for modeling the response of a large-area scintillator sensor to ionizing radiation, explicitly including resolution-broadening effects of scintillation light generation, propagation, and collection is also described.

Authentication of radiation measurement systems for nonproliferation

Radiation measurement systems are central to the affirmation of compliance with a variety of agreements related to arms-control and non-proliferation. Authentication is the process by which the Monitoring Party gains appropriate confidence that the information reported by a monitoring system accurately reflects the true state of the monitored item. Authentication utilizes a set of tools to provide evidence that a system performs its required and defined tasks. These tools include: functional testing using trusted unclassified calibration sources, evaluation of documentation including the software, evaluation of hardware, random selection of hardware and software, and usage of tamper indicating devices. Procedures for carrying out authentication are central to the successful implementation of the complex process of authenticating systems throughout their lifecycle. The lifecycle of a system can be divided into the elements of design, fabrication, installation, and operations. Radiation measurement systems are being built for use in the Russian Federation that will be the subject of US authentication activities.

Methods for Attribute Measurement and Alternatives to Multiplicity Counting

The Attribute Measurement System with Information Barrier (AMS/IB) specification is being developed in support of the Defense Threat Redcution Agencys (DTRAs) Cooperative Threat Reduction (CTR) program for the Mayak Fissile Material Storage Facility. This document discusses the technologies available for attribute measurement, and advantages and disadvantages of alternatives.

Progress Report on the Advanced Large-Area Plastic Scintillators (ALPS) Project

The U.S. Department of Energy tasked Pacific Northwest National Laboratory to investigate possible technological avenues for substantially advancing the state-of-the-art in gamma detection via large-area plastic scintillators. This letter report describes progress to date on this project. Early phases of the project, which commenced in January 2003, have focused on (1) quantifying the light-collection efficiency in plastic scintillator sheets as a function of photomultiplier tube positioning and edge-area coverage, (2) developing a conceptual design for a demonstration sensor, and (3) conducting initial laboratory setup and preliminary experiments using relatively small plastic scintillators for readout technique development and benchmarking of the modeling studies.