Methodology for a fast determination of EDX Si(Li) detector response function in the 5 keV to 15 keV range (original) (raw)
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Accurate calibration of a Si(Li) detector for PIXE analysis
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1984
Two methods for obtaining thin target PIXE K, calibration factors were compared. The first (relative or experimental) method relied on two different sets of accurate thin film standards, while the second (absolute or theoretical) method involved the use of fundamental physical parameters and an experimental investigation of the Si(Li) detector's detection efficiency. Several critical facets of the calibration procedures are discussed or were carefully investigated. These include the incident beam energy determination, beam current integration, accuracy of thin film standards, solid angle and window thicknesses (Be, Au, Si) of the Si(Li) detector, net K, peak area determination and tail-to-peak ratio as a function of X-ray energy, fluorescence yields and ionization cross sections. The experimental and theoretical calibration factors finally obtained showed excellent agreement, the average difference being only-3.5%.
Characterization of a Si(Li) detector for PIXE analysis
Journal of X-Ray Science and Technology, 1994
The characterization ofa Si(Li) detector used for PIXE analysis is presented. The main detector parameters are indicated, and the different methods of determining them are examined. Also, the detection efficiency has been measured in the 1.4-100 keV photon energy range, using calibrated radioactive sources and PIXE, to obtain and compare the fitted parameters. Finally, the fit of an analytic function to the measured efficiency values and the efficiency in parametric form are compared, and the advantages observed for each are noted.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1989
The particle-induced X-ray emission (PIXE) method with use of thin evaporated and ion-implanted targets and 'II and 4He ion impact, combined with the standard X-ray source technique, is applied to determine the efficiency of a Si(Li) detector in the photon energy range 1.5-150 keV. An existing database for the efficiency dete~nation by PIXE method is discussed in detail. Special care has been devoted to the reliable reproduction of the Si-K and Au-M absorption edge structure which strongly affect the low-energy part (1.5-4 keV) of the efficiency curve. Fox this purpose, it has been found necessary to measure the thickness of the detector Au contact by the fluorescence method, to fit then uniquely the thickness of a uniform Si dead-layer. It has been also demonstrated that the observed efficiency increases in the intermediate photon energy region (6-20 kev) can be well described assuming the existence of an additional peripheral Si dead-layer. An extended Si(Li) detector model including this effect is proposed. The procedure developed for the efficiency determination is applied to monitor the Si(Li) detector parameters over a year. During which the increase of an ice build-up layer with time was observed.
Current Trends in Si(Li) Detector Windows for Light Element Analysis
X-Ray Spectrometry in Electron Beam Instruments, 1995
Over the last 10 years much of the progress in x-ray spectroscopy has been in the area of light element analysis. In wavelength dispersive spectroscopy, this has resulted from the development of multilayer synthetic crystals. In energy dispersive spectroscopy, this has resulted from the development of new window technologies. Energy dispersive Si(Li) detectors have become more sensitive over the years, until the window can be the limiting factor in light element x-ray analysis. The window allows x-rays to pass and protects the detector from light and gases. It must withstand atmospheric pressure and repeated pressure cycling. Several technologies have been developed for this purpose.O,2) An EDX system for light element analysis requires more than just a thin window. The detector, preamp, electronics, and software all contribute to light element performance. I do not intend to discuss these issues in this paper, but it is important to remember that a system for light element analysis should be purchased on its performance as a system, and not just on the basis of the window. There are basically six different window technologies used for light element analysis. Of these, most are proprietary, meaning that they are available on only one EDX manufacturer's instruments. The two windows that are not proprietary are the MOXTEK polymer window and the diamond window. All manufacturers of Si(Li) detectors have qualified the MOXTEK window, and the same is true of the diamond window. Therefore, these windows can be requested of any EDX manufacturer.
Asymmetry of characteristic X-ray peaks obtained by a Si(Li) detector
Spectrochimica Acta Part B: Atomic Spectroscopy, 2007
The asymmetry of the characteristic X-ray peaks obtained using a Si(Li) detector is mainly due to incomplete charge collection. Impurities and defects in the crystalline structure of Si can act as "traps" for holes and electrons in their trip toward the detector electrodes. Therefore, the collected charge, and consequently the detected energy, is smaller than the expected one. The global effect is that peaks may present a "tail" toward the low energy side. This phenomenon is more important for low energies (lower than 2.3 keV, in the case of the detector characterized). In this work, the parameters related to peak asymmetry were studied, allowing a better understanding of the trapping process mentioned above. For this purpose, spectra from mono-and multi-element samples were collected for elements with atomic number between 7 and 20. In order to describe the shape of the characteristic K peaks as a function of its energy, an asymmetric correction to a Gaussian function was proposed. Spectra were obtained by electron probe microanalysis for incidence energies between 5 and 25 keV using an energy dispersive spectrometer equipped with an ultra-thin window Si(Li) detector. It was observed that the area corresponding to the asymmetric correction exhibits an energy dependence similar to that of the mass absorption coefficient of the detector material. In addition, other two spectrometers were used to investigate the dependence of tailing on the detection system. When two spectrometers with the same kind of detector and different pulse processors were compared, peaks were more asymmetric for lower peaking time values. When two different detectors were used, differences were even more important.
Combining CdTe and Si detectors for Energy-Dispersive X-Ray Fluorescence
X-Ray Spectrometry, 2012
Most energy-dispersive X-ray fluorescence (EDXRF) instruments use Si diodes as X-ray detectors. These provide very high energy resolution, but their sensitivity falls off at energies of 10-20 keV. They are well suited for measuring the K lines of elements with Z < 40, but for heavier elements, one must use K lines at low efficiency or use L or M lines that often overlap other lines. Either is a challenge for accurate quantitative analysis. CdTe detectors offer much higher efficiency at high energy but poorer energy resolution compared with Si diodes. In many important EDXRF measurements, both high and low Z elements are present. In this paper, we will compare the precision and accuracy of systems using the following: (1) a high resolution Si detector, (2) a high efficiency CdTe detector, and (3) a composite system using both detectors. We will show that CdTe detectors generally offer better analytical results than even a high resolution silicon drift detectors for K lines greater than 20 or 25 keV, whereas the high resolution Si detectors are much better at lower energies. We will also show the advantages of a combined system, using both detectors. Although a combined system would be more expensive, the increased accuracy, precision, and throughput will often outweigh the small increase in cost and complexity. The systems will be compared for representative applications that include both high and low Z elements.
Peripheral imperfections and their effects on efficiency in Si(Li) X-ray detectors
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1984
The results of scanning a finely collimated beam of 5.9 keV X-rays across the faces of three different Si(Li) X-ray detectors are interpreted in terms of an active area of good charge collection and peripheral regions of incomplete charge collection, both within the manufacturers' stated areas. The data are correlated with absolute efficiencies determined using calibrated radionuclide X-ray ekitters. The hazards of spectral artefacts from the imperfect regions in the contexts of XRF and PIXE are stressed.
X-ray detectors and spectrometers
Ultramicroscopy, 1989
X-ray emission spectroscopy using focused electron beams to excite thin specimens provides elemental analysis with very high spatial resolution. The lithium-drifted silicon energy-dispersive spectrometer (EDS) is the only X-ray detector widely used in the analytical electron microscope (AEM). Future AEMs may employ an intrinsic germanium EDS detector to detect heavy-element K lines in addition to a Si(Li) detector optimized to detect the light elements such as O, N, C, B and possibly Be. The advantages of the wavelength-dispersive crystal spectrometer (WDS) complement those of EDS detectors and may be useful in an AEM optimized for high-spatial-resolution X-ray emission spectroscopy.