Measurement of reactor tube cladding thickness by x-ray fluorescence spectrometry

An x-ray fluorescence spectrometer was designed and fabricated which nondestructively determines the thickness of aluminum cladding at small suspected thin spots in the inner or outer surface of actinide reactor tubes. The analysis method is based on the difference in absorption of actinide L/sub ..cap alpha../ and L/sub ..beta../ fluorescent x-rays in passing through the cladding. Calibration plots of the logarithm of the L/sub ..beta..//L/sub ..cap alpha../ x-ray intensity ratio versus cladding thickness are linear to at least 40 mils for U-Al, U/sub 3/O/sub 8/-Al, and PuO/sub 2/-Al substrates. Accuracy and precision of the experimentally determined cladding thickness and evaluated for both uranium and plutonium substrates. Experimental thickness data are reported for 618 quality assurance analyses on six Mark 41 PuO/sub 2/-Al target tubes. An x-ray fluorescence cladding thickness monitor operated with a computer-controlled fluoroscope holds considerable promise for quality assurance because (1) a permanent record of cladding thickness for each reactor tube would be provided and (2) the cladding integrity of each tube would be assured before irradiation in the reactor

An improved analytical detector response function model for multilayer small-diameter PET scanners

The optimization of spatial resolution is a critical consideration in the design of small-diameter positron emission tomography (PET) scanners for animal imaging, and is often addressed with Monte Carlo simulations. As a faster and simpler solution, we have developed a new analytical model of the PET detector response function, and implemented the model for a small single-slice, multilayer PET scanner. The accuracy of the model has been assessed by comparison with both Monte Carlo simulations and experimental measurements published in the literature. Results from the analytical model agreed well with the Monte Carlo method, being noise free and two to three orders of magnitude faster. The only major discrepancy was a slight underestimation of the width of the point spread function by the analytical method as inter-crystal scatter is neglected. We observed good agreement between the predictions of the model and experimental measurements. For two large-diameter scanners additional discrepancies were seen due to photon acollinearity, which is not considered in the model. We have shown that the simple and fast analytical detector response function model can provide accurate estimates of spatial resolution for small-diameter PET scanners, and could be a useful tool for several applications, complementing or cross-validating other simulation methods