Nondestructive measurements of x-ray and gamma-ray emissions can be used to determine the abundances of various actinides in a sample. Volume 1 of this report describes the methods and algorithms we have developed to determine the relative isotopic abundances of actinides in a sample, by analyzing gamma-ray spectra obtained using germanium detector systems. Volume 2 is a guide to using the MGA (Multiple Group Analysis) computer program we have written to perform plutonium isotopic analyses. The code requires no calibrations and can be used to measure virtually any size and type of plutonium sample. Measurement times can be as short as a few minutes; measurement accuracies are typically within 1 or 2%.
GRPANL is a general-purpose peak-fitting program that calculates gamma-ray and x-ray energies and intensities from a given spectral region. The program requires that the user supply input information such as the first and last channels of the region, the chan nels to be used as pre-and post-region background, the system gain and zero-intercept, and a list of approximate energy values at which peaks occur in the region. Because the peak position and peak-shape parameters enter nonlLaearly into the peak-fitting algorithm, an iterative least-square procedure is used in the fitting process. The program iterates until either all convergence criteria are met or ten iterations have elapsed. The code described here allows for twenty free parameters and a region as large as 240 data channels. This code runs on an LSI-11 computer with 32K. memory and disk-storage capability.
High-resolution, gamma-and X-my spectrometry are used routinely in nuclear materials safeguards vetication measurements. These measurements are mostly performed with high-purity germanium (HJ?Ge) detectors, which require cooling at liquid-nitrogen temperatures, thus limiting their utility in field and unattended safeguards measurement applications. Sodium iodide (NaI) scintillation detectors do not require cooling, but their energy resolution (10% at 122 keV) is insu&ient for many verification measurements. Semiconductor detectors that operate at room temperatures, such as cadmium-zinc-telhuide (CZT) detectors, with energy resolution performance reaching 2.0% at 122 keV may be used for certain safeguards verification applications. We have developed hardware to utilize CZT detectors in X-and gamma-ray measurement ,systems and software to apply such a system in measuring 215U enrichment for safeguards verification purposes. The paper reports on the CZT detector-based measurement system and measurement results obtained with it. The paper also discusses work on additional improvements to broaden the applications of the system.
Cadmium Zinc Telluride (CZT) detectors are the highest resolution &om-temperature gamma ray detectors available for-. The model and the peak-shape parameterization as a function of energy will be presented.
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