783620H / 1013 1. INTRODUCTION
1.1.2. Analysis and Display Tools
GammaVision is designed to analyze spectra generated by any ORTEC MCB, directly from the spectrum on display or from spectrum files on disk, in any of several file formats including the advanced and archivable
.SPC
format. In addition, GammaVision can directly read and write spectral data files in the
.SPE
ASCII file format.
GammaVision offers five analysis engines and three major analysis methodologies. In the primary analysis method, a library-directed peak search delivers lower detection limits than can be achieved by “unguided” peak searches. This method is ideally suited for the determination of low-level and ultra-low-level samples (where statistics might be poor) for a specified list of nuclides. For analysis of true unknowns (e.g., emergency-response samples), an “Auto Isotope
Identification” mode allows efficient, accurate use of large libraries while maintaining reasonable analysis times. The interactive re-analysis mode lets you repeatedly re-fit the spectrum while monitoring the fit residuals. This is invaluable for highly complex spectral analyses such as certain neutron-activation and reactor-coolant spectra. A “directed fit” option lets you report negative activity values if calculated, as required for some effluent analysis requirements. An enhancement to directed fit allows this option to be used in the deconvolution of overlapping peak areas.
After analysis, evaluate the results using the flexible, easy-to-read GammaVision report or a variety of onscreen, informative plotting routines. For custom-configured reports, we offer the optional GammaVision Report Writer (A44-BW), which uses an Access-format database and
SAP
®
BusinessObjects Crystal Reports™. In addition, we offer Global Value™, which allows for a variety of custom calculations using ASCII-text, templates, analysis data editing tools, and several additional data inputs commonly used in nuclear power plant applications.
1.2. MCA Emulation
An MCA, in its most basic form, is an instrument that sorts and counts events in real time. This sorting is based on some characteristic of these events, and the events are grouped together into bins for counting purposes called channels. The most common type of multichannel analysis, and the one of greatest interest to nuclear spectroscopists, is pulse-height analysis (PHA).
PHA events are signal pulses originating from a detector,
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and the characteristic of interest is the pulse height or voltage, which is proportional to the particle or photon energy. An analog-to-
digital converter (ADC) is used to convert each pulse into a channel number, so that each
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In this manual, “Detector” (capitalized) means the transducer (high-purity germanium, sodium iodide, silicon surface barrier, or others) plus all the electronics including the ADC and histogram memory. The transducers are referenced by the complete name, e.g., high-purity germanium (HPGe) detector.
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