Abstract
A new application (known as “VRF”, or “Visual RobFit”) for analysis of high-resolution gamma-ray spectra has been developed using non-linear fitting techniques to fit full-spectrum nuclide shapes. In contrast to conventional methods based on the results of an initial peak-search, the VRF analysis method forms, at each of many automated iterations, a spectrum-wide shape for each nuclide and, also at each iteration, it adjusts the activities of each nuclide, as well as user-enabled parameters of energy calibration, attenuation by up to three intervening or self-absorbing materials, peak width as a function of energy, full-energy peak efficiency, and coincidence summing until no better fit to the data can be obtained. This approach, which employs a new and significantly advanced underlying fitting engine especially adapted to nuclear spectra, allows identification of minor peaks that are masked by larger, overlapping peaks that would not otherwise be possible. The application and method are briefly described and two examples are presented.
Highlights
IntroductionApplications for nuclear spectral analysis that are in wide use for commercial applications typically begin with a peak search (such as the Mariscotti [1] method of second derivatives), and match the energies and areas of the peaks that were found to nuclear tables to determine the activities of nuclides evident in the spectrum, taking into account calibrations for energy, resolution (or "peak-width"), and detector efficiency
Applications for nuclear spectral analysis that are in wide use for commercial applications typically begin with a peak search, and match the energies and areas of the peaks that were found to nuclear tables to determine the activities of nuclides evident in the spectrum, taking into account calibrations for energy, resolution, and detector efficiency
Each analysis step consists of a series of iterations seeking a best fit while varying the activities of each emitter and the user-enabled parameters of energy calibration, resolution calibration, detector full-energy peak efficiency, and attenuation by intervening compounds or mixtures of material
Summary
Applications for nuclear spectral analysis that are in wide use for commercial applications typically begin with a peak search (such as the Mariscotti [1] method of second derivatives), and match the energies and areas of the peaks that were found to nuclear tables to determine the activities of nuclides evident in the spectrum, taking into account calibrations for energy, resolution (or "peak-width"), and detector efficiency This approach has difficulty resolving peaks that lie closely together unless they are sufficiently well separated in energy, have comparable areas, and have sufficient counting statistics. RobFit was described by Lasche [6], but the graphical implementation lacked many essential capabilities for practical analysis, the library was severely limited, and the interface that applied nuclear spectral data to RobFit had only limited capabilities for calibration, no gamma emission line search capability, crude efficiency fitting methods, inefficient continuum fitting methods, and no means of identifying or resolving coincidence summing peaks. All of these limitations have been overcome with an entirely new implementation of a greatly improved interface to RobFit called "Visual RobFit", or “VRF” for short
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