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Abstract  

SYNTH, a WindowsTM based software package developed for generating synthetic gamma-ray spectra, has been updated and extended to include the ability to generate gamma-ray spectra resulting from neutron activation. Along with a new gamma-ray library (based on the NNDC PCNuDat compilation), and the best available neutron cross-sections, it is now possible to simply, and quickly predict the interference effects of different bulk and trace element compositions by generating a synthetic gamma-ray spectrum that will be representative of a specific set of input parameters. The parameters include, but are not limited to: elemental composition (bulk, and trace) of the sample; irradiation, decay, and count times; thermal, and resonance neutron flux; sample to detector distance; detector specifications; and electronics configuration. Using existing data reduction codes, it is then possible to generate Minimum Detectable Activities (MDA's) for other trace elements that you may wish to detect in this type of matrix.

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Abstract  

Uranium was measured in eight biological standards at the part-per-billion level. Matrix effects encountered in the use of liquid standards are discussed.

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Summary  

{\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}} \viewkind4\uc1\pard\f0\fs24 The use of HPGe detectors in counting situations where the sample is not easily reproduced has increased the use of models to determine the counting efficiency for the specific geometry. The accuracy of these simulations of the germanium detector response relies on detailed knowledge of the performance of the detector. Several different types of detectors were measured at different energies using a pencil beam of gamma-rays. These measurements showed that the dead layer was not uniform from detector to detector. This and the construction details were used to calculate the efficiency for several detectors. \par }

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Abstract  

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.

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Abstract  

A pilot plant is being designed at the U. S. Department of Energy's Savannah River Site (SRS) to demonstrate the removal of 90Sr, 137Cs, 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 60Co, 137Cs, and 90Sr 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.

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Abstract  

An implementation of the Electron Gamma Shower 4 code (EGS4) has been developed to allow convenient simulation of typical gamma ray measurement systems. Coincidence gamma rays, beta spectra, and angular correlations have been added to adequately simulate a complete nuclear decay and provide corrections to experimentally determined detector efficiencies. This code has been used to strip certain low-background spectra for the purpose of extremely low-level assay. Monte Carlo calculations of this sort can be extremely successful since low background detectors are usually free of significant contributions from poorly localized radiation sources, such as cosmic muons, secondary cosmic neutrons, and radioactive construction or shielding materials. Previously, validation of this code has been obtained from a series of comparisons between measurements and blind calculations. An example of the application of this code to an exceedingly low background spectrum stripping will be presented.

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Abstract  

High-level radioactive wastes can be transformed to low-level wastes by removing137Cs through selective ion exchange processes. Since the short-lived daughter,137inBa produces the 662-keV gamma-ray normally attributed to137Cs, equilibrium may be broken, and observation of the 662-keV gamma-ray cannot be used to detect cesium breakthrough. Two detectors viewing the output line, but separated sufficiently to measure the137mBa decay between them, are used to detect137Cs breakthrough based on deviation from the normal137mBa decay. Detection evaluated for the process separation time, counting time, fractional breakthrough detectable, and accuracy and confidence of the measurements are discussed.

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Abstract  

An automated delayed neutron counting and instrumental neutron activation analysis system has been developed at Los Alamos National Laboratory's Omega West Reactor (OWR) to analyze samples for uranium and 31 additional elements with a maximum throughput of 400 samples per day. The system and its mode of operation for a large reconnaissance survey will be described.

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Abstract  

The necessity to monitor international commercial transportation for illicit nuclear materials resulted in the installation of many nuclear radiation detection systems in Portal Monitors. To overcome the difficulty of innocent alarms due to a large content of natural radioactivity or medical nuclides, Department of Homeland Security (DHS) supported the writing of the ANSI N42.38 standard (Performance Criteria for Spectroscopy-Based Portal Monitors used for Homeland Security) to define the performance of a portal monitor with nuclide identification capabilities, called a Spectroscopy Portal Monitor. To accomplish the necessary performance, several different HPGe detector configurations were modeled using MCNP for the horizontal field of view (FOV) and vertical linearity of response over the detection zone of 5 meters by 4.5 meters for 661 keV as representative of the expected nuclides of interest. The configuration with the best result was built and tested. The results for the FOV as a function of energy and the linearity show good agreement with the model and performance exceeding the requirements of N42.38.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: W. Hensley, A. McKinnon, H. Miley, M. Panisko, and R. Savard

Abstract  

A computer code has been written at the Pacific Northwest Laboratory (PNL) to synthesize the results of typical gamma-ray spectroscopy experiments. The code, dubbed SYNTH1, allows users to specify physical characteristics of a gamma-ray source, the quantity of the nuclides producing the radiation, the source-to-detector distance, the type and thickness of absorbers, the size and composition of the detector (Ge or NaI), and the electronic set up used to gather the data. In the process of specifying the parameters needed to synthesize a spectrum, several interesting intermediate results are produced, including a photopeak transmission function vs. energy, a detector efficiency curve, and a weighted list of gamma and x rays produced from a set of nuclides. All of these intermediate results are available for graphical inspection and for printing. SYNTH runs on personal computers, is menu driven and can be customized to user specifications. SYNTH contains robust support for coaxial germanium detectors and some support for sodium iodide detectors. SYNTH is not a finished product. A number of additional developments are planned. However, the existing code has been carefully compared to spectra obtained from National Institute for Standards and Technology (NIST) certified standards with very favorable results.

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