Dış Kaynaklı Proje Süreçleri Yönetim Sistemi
The traditional technique for uranium isotope abundance measurements is a destructive assay using mass spectrometry. In recent years, a number of studies have explored use of gamma ray spectrometry (GRS), a nondestructive method of assay. This method offers a number of advantages such as the cost for the equipment and the analysis are substantially less than the mass spectrometry cost and most importantly the equipment can be made portable for in-situ measurements and also measurement time is short thereby allowing quick turn-around of results for possible safeguard and nuclear security applications. Thus, among the nuclear material characterization techniques, gamma ray spectroscopy is the most common one due to its field applicability. Because the most important thing for analysts is to obtain the correct information regarding a nuclear or other radioactive material within a short time and without changing the physical form of the material. It has already demonstrated by Gunnink (1990); Gunnink et al.(1994) and Parker et al. (1999) that GRS is a high fidelity technique in practice, which can be used both in field and Iaboratory conditions for the determination of depleted uranium (DU < 0.72%U-235), natural uranium (NU, 0.72% U-235), low enriched uranium (LEU, 0.72%-19.99% 235U) and of highly enriched uranium (HEU >20%U-235).
The isotopes of uranium emit alpha, beta, neutron, and gamma radiation. The primary radiation of uranium samples is gamma radiation, which is usually dominated by emissions from U-235 decay. The 185.7 keV gamma ray is the most frequently used signature to measure U-235 enrichment. It is the most prominent single gamma ray from any uranium sample enriched above natural U-235 levels. In the simplest case of low U-235 enrichment, U-235 and U-238 are essentially the only components. Since the sum of their isotopic fractions (f) is then equal to 1, the isotopic abundance of U-235 (in other words; U-235 atom enrichment) can be obtained from the Equation 1 (See Annex-1). In experimental measurements, it is important to use the correct analytical methods to ensure the true isotopic identification of a nuclear material (NM) sample. In this study, the proposed procedures are based on low energy (185.7 keV, U-235) and high energy (1001 keV, 234mPa (daughter of U-238)) peaks in the spectrum when the samples are measured with CdZnTe semiconductor detectors. For a HPGe detector, the more complex spectrum was deconvoluted due to its having better energy resolution of a special HPGe detector, however, in this case, the effects of the parameters such as absorber thickness between the sample-detector, counting time to the detection and uranium isotopic abundance measurement accuracy were investigated when multigroup gamma-ray analysis procedure is employed. For the measurements to be performed, the certified uranium standards(EC-NRM171) were counted near the other radioactive sources to analyze the real uranium spectrum interference from other source(s) spectra because some analytical peak regions were complicated by additional source spectrum. In such cases, the results from MGAU or U- 235View multigroup gamma-ray analysis were also used for the comparison. Specific analytical methods for this technique based on CdZnTe detectors were also be developed. For gamma spectroscopic analytical approaches, to measure uranium isotopic abundances with minimum error, corrections for spectral interferences were investigated. In addition, in the spectral analysis of uranium complex uranium spectra, especially in the low energy (up to 300 keV) and high energy (up to 1200 keV) regions, isotope abundances were subjected for this study. In these spectra for the case of the uranium samples masked by other radioactive sources that emit X- and gamma-rays overlapping uranium spectrum, new approaches to correct the contribution of spectral interference peaks that affect the analytical peaks were proposed. For the accuracy of U-235 enrichment analysis, absorber effects were investigated in the HPGe detector measurements. Thus, the project provides as its objective the information needed for effective and efficient use of nuclear detection devices for determining the accuracy and sensitivity of detectors (a full range of low, medium, and high resolution detectors including LaBr3, CdZnTe, HPGe etc.) in detecting, identifying and characterizing nuclear materials under various shielding, masking, time, temperature, and other interference scenarios.