Uranium Enrichment Determination Using The CdZnTe Spectrum In 88-100keV Region

CdZnTe detector is a new type semiconductor detector. Its energy resolution is better than NaI(Tl) detector but worse than HPGe detector. It is smaller in size, lighter in weight, and more stable than traditional detectors in room-temperature applications, so it is widely used in nuclear safeguards. In this work, a method is brought out to determine the uranium enrichment by analyzing the CdZnTe spectrum in 88-100keV region, through the y -rays and X-rays emitted from uranium isotopes and their daughters. A code is developed, and the method is verified through its analysis results.Uranium enrichment means the ratio of the combined weight of the isotopes 233U and 235U to that of the total uranium in question. Uranium isotopes and their daughters emit -rays and X-rays during the decay process, their peak area and relative efficiency can be calculated through spectrum analysis. The number of 238U nuclei can be calculated by the 92.38 keV and 92.80 keV peaks of 234Th generated by the 238U - 234Th decay balance, and the number of 235U can be calculated by the 89.95 keV and 93.35 keV K peaks generated by internal conversion of 235U - 231Th decay system. Then the ratio of uranium isotopes can be obtained and the uranium enrichment can be determined. In the analysis process, the six main peaks in 88 - 100 keV region, including the y peaks of 234Th, the K peaks of Th and the K peaks of U, are chosen. The smoothly joined Gaussian function and low energy exponential tail is taken as peak shape function and quadratic polynomial is taken as background function. The two functions are fitted together to calculate the peak area. The efficiency of all peaks in this region is considered equivalent approximately, so the uranium enrichment can be determined finally.According to the theory, a numerical method is brought out and its kernel is least square fit. The linear least square fit is used in energy calibration and geometrycalibration, and the nonlinear least square fit is used in peak fitting and region fitting. Several spectra with various enrichments are analyzed in different conditions, the best condition of fitting is obtained, and the best results are achieved.For the CdZnTe spectrum with worse resolution, the analysis results show that the method can distinguish high-enriched uranium and low-enriched uranium, and work out the enrichment data in low precision. At the same time, the code can be used in HPGespectrum analysis. In the enrichment range of 1% -90 %, the accuracy is about 10%.