Omni Scientific Instruments, Inc.

- Version XRFWIN 3.1 - Comprehensive Softwar

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XRFWIN is a comprehensive software package for performing X-ray fluorescence spectroscopy (XRF). XRF involves measuring the intensity of x-rays fluoresced from a specimen subjected to a high-energy flux as a function of energy or wavelength. The incident flux is termed the primary radiation. Peaks in the fluoresced energy or wavelength spectra correspond to characteristic emission 'lines' of atoms present in the specimen. The identification of characteristic atomic x-ray lines is known as qualitative analysis. The intensity of a characteristic line is proportional to the quantity of the associated atom in the specimen. This intensity is modified by absorption or enhancement in the specimen, known as matrix effects. The determination of element concentration by measuring characteristic line intensity and correcting for matrix and instrument effects is known as quantitative analysis.

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There are two fundamental types of XRF spectrometers: wavelength dispersive (WD) and energy dispersive (ED). WD spectrometers measure the radiated x-rays from a specimen by selecting wavelength using an analyzing diffraction crystal. ED spectrometers measure the radiated x-rays from a specimen by selecting energy in the channels of a multi channel analyzer (MCA). WD spectrometers generally have better wavelength resolution than the energy resolution in ED spectrometers. Because of peak broadening caused by the detectors used in ED spectrometers, WD spectrometers are generally more sensitive than ED spectrometers. WD spectrometers are also generally larger, more expensive, slower, and more complicated to operate than ED spectrometers.

The other aspect to any XRF spectrometer is the means by which the sample is irradiated to induce fluorescence. Because WD spectrometers generally involve long path lengths from source to detector and given losses inherent in the analyzing crystal goniometer, a large energy radiation source is required. This combined with the desire to enhance the good sensitivity of WD spectrometers and the preference for systems where the specimen need not be conductive mean that WD spectrometers usually utilize high power x-ray tubes. The use of WD spectrometers is usually referred to as just WDS. With ED spectrometers one is usually not trying to maximize sensitivity or accuracy. Rather, the spectrometer is often taking advantage of the small size, low power requirements or high speed of ED spectrometers, or is used as an add-on to other instrumentation. EDX spectrometers utilize x-rays to irradiate the sample. These x-rays could originate from an radioactive x-ray source, or an x-ray tube. EDS spectrometers irradiate the sample with high energy electrons. Examples are the dedicated electron microprobe, or attachments often provided with scanning electron microscopes (SEM's). A radioactive beta source could also be utilised. PIXE, or Proton-Induced X-ray Emission, irradiates the specimen with high energy protons. These could originate from a radioactive proton source or particle accelerator.

Once ejection of inner orbital electrons is achieved, the matrix processes of x-ray absorption and enhancement are the same in all types of XRF spectroscopy, and different versions of XRFWIN under the Windows operating systems are available for all these types of spectrometers. Software instrument drivers fully integrate operation of the instrument with the software. A comprehensive design simplifies the management and operation of the instrument, management of the data, and analysis of the data through an intuitive user interface. See the following links for details of the various versions of XRFWIN:

Traditional XRF software has focused on the design of the instrument with secondary consideration for the task at hand - chemical analysis using XRF. In widespread use since 1996, XRFWIN has revolutionised XRF analysis by putting chemical analysis first. A comprehensive database of the elements allows qualitative analysis to be performed with the click of a button. The core of quantitative analysis is the XRFWIN material. Fully integrated instrument control is achieved by plug-in instrument drivers. As instrument settings are made through an instrument abstraction layer, materials defined for one instrument can be rapidly converted to other instrument brands and models. This is particularly attractive for large operations where there is a desire to share results and analysis procedures.

Figure 1.1. Versions of the XRFWIN product line. Note that instrument drivers are fully integrated into the software.

The XRFWIN Material

Quantitative analysis of a specimen is managed in the software by the XRFWIN material. The material consists of a list of elements that will be measured in the specimen. As each element may be associated with an unmeasurable element such as oxygen, each measured element is referred to as an analyte. For each analyte the user defines the line to be measured, the stoichimetry of the compound (such as the type of oxide), and a set of instrument-specific settings. For WDS instruments, this includes a set of background measurements to be made. The user also specifies any known constituents in the specimen such as in a flux preparation, and a list of standards to be used with specimens of the material. Finally, the material includes a data reduction method used to convert measured counts to analyte concentrations. A variety of methods are available including the methods of Lucas-Tooth and Pyne, Lachance and Traill, Claisse and Quintin, Rasberry and Heinrich, trace analysis using ratios, simple interpolation polynomials, and the fundamental parameters (FP) method. Internal linking of the material file with the true FP algorithm of XRFWIN means that an uncompromising, near standard-less analysis is possible.

Figure 1.2. Typical WDS material settings.

Inclusion of standards in the material simplifies their management and allows the automated taking of standard counts. It also simplifies calibration of the various data reduction methods. As the material is included with any set of results for a run of the spectrometer, the analysis of a set or results following a run can be re-worked and manipulated away from the spectrometer providing the ultimate in flexibility.

Fundamental Parameters

The XRFWIN material makes utilising FP in your analysis a breeze. The FP algorithm of XRFWIN is a true FP algorithm making direct use of the simultaneous set of integral equations prescribed by the Sherman equations. No approximations or intermediate 'synthetic' standards are incorporated during analysis, so you can be sure that results are uncompromising. The user can choose between allowing the algorithm to automatically select a standard close in composition to the unknown, or to use a fitted instrument response curve to speed up computation. It is even possible to include analytes for which no standard is available. Further, the FP algorithm provides a number of options to include analysis of unmeasured analytes in the specimen.

Instrument Drivers

Direct instrument control is achieved by plug-in instrument drivers. These drivers provide a user interface that is fully integrated into the XRFWIN material editing user interface meaning that the user need only look one place when setting up for a quantitative run of the spectrometer. In principle any instrument with a remote interface can be supported. Contact us with your specific instrument configuration for details.

Figure 1.3. WDS Analyte settings for the Rigaku S/MAX 3080 showing both general and instrument-specific analyte settings.

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