A 23% analysis code, U235, has been written that can nondestructively determine the percentage of 23% in a uranium sample from the analysis of the emitted gamma rays. The code is operational and work is now underway to improve the accuracy of the calculation, particularly at the high (>go%) and low (<0.7%) 235U concentrations. A technique has been found to evaluate low 235U concentrations that works well on the existing standards. Work is now under way to evaluate this technique for other detectors and other types of samples. Work is also proceeding on: (1) ways to better determine gamma backgrounds, (2) techniques to determine the equivalent thickness of the sample to correct for gamma attenuation, (3) evaluation of the existing data base of branching ratios of 35U, 238U and their daughters gamma rays to allow better results and (4) evaluation of the existing data base on the emission ratios for uranium, thorium, and protactinium x-rays. Introduction: Gamma ray spectrometry can be used to analyze uranium isotopic abundance ratios. The "standard" uranium enrichment meter relies on making standards of the various sample types of interest. Analyzing these standards with mass spectrometry to find the appropriate calibration factors is then done to calibrate out all the unknowns in the counting scheme. Then the strong 235U gamma peak at 185.712 keV can be counted with a "simple" two channel analyzer to find the peak counts and background. The net 185.715 counts are used to calculate the enrichment. This technique works well but has the draw back that new "standards" have to be made for each different geometry and analyzed by mass spectrometry. This calibration process is often very time consuming and costly as well as being limited to "calibrated" geometries. Accurate analysis of a radioactive sample by high resolution Germanium detector spectrometry requires correct information on the gamma ray and x-ray branching ratios for the radionuclides in the sample. 23% and 238U sample analysis is complicated in that the gammas observed often come from their radioactive daughters produced by successive alpha and beta decays. In addition to gamma decay these elements decay by internal conversion, IC, and subsequent
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.
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