Contents of Chapter.
Desk Top Spectrum Analyzer (DTSA) is a computer program for the generation, interpretation and analysis of x-ray spectra generated by focused electron beam bombardment of specimens. It was created for a number of reasons. The most important reason was the absence of a simple way to study the physical and statistical aspects of an energy dispersive spectroscopy (EDS) analytical problem other than actually preparing calibration standards and specimens, measuring spectra and analyzing them. DTSA will emulate the specimen properties and experimental environment to generate spectra reflecting the relevant physics, chemistry and statistics of a specimen under electron bombardment, thus permitting a rapid but detailed study of a potential analytical problem at the desktop. The analyst is able to determine an expected mean value, the variance about this mean, and an accurate estimate of the minimum detectable limit (MDL) for a given element in a given matrix on a particular instrument.
DTSA permits the detailed analysis of a collection of acquired EDS or WDS spectra at one's desktop, freeing the expensive analytical electron column instrument and its associated x-ray analysis system for data acquisition.
The program requires a minimum of 9 megabytes of memory in a Power Macintosh type computer with a color, or monochrome, monitor (The current program will work with 256 colors The new version of the DTSA program will not run on older Macintosh or PC computers. The program is System 7 or 8 compatible and will function in 32 bit mode. With an appropriate Nu-buss or PCI card installed in the computer, the program can also acquire x-ray spectra directly.
DTSA is a fully functioning multichannel analyzer that performs all of the functions expected in a Multi-Channel Analyzer (MCA) plus much more. The program provides all of the usual scaling operations, peak markers and region-of-interest operations. The program has incorporated many of the accepted data analysis procedures developed over many years at the National Institute of Standards and Technology (NIST), (formerly the National Bureau of Standards) in Gaithersburg, MD and the National Institutes of Health (NIH) in Bethesda, MD, as well as procedures such as CITZAF, Cliff-Lorimer, and the Hall method for biological analysis.
NIST and NIH will use their best efforts to deliver a high quality program/database and to verify that the procedures and data contained therein have been selected on the basis of sound scientific judgment. However, NIST and NIH make no warranties to that effect, and shall not be liable for any damage that may result from errors or omissions in the program or the database. Furthermore, at several places in this documentation, and in the program itself, reference is made to commercial manufacturers of equipment. These references in no way are to be construed as a recommendation or an endorsement.
A. Multiple linear least squares ( MLLSQ) procedure is extremely fast and accurate but requires reference spectra and finds only peak intensities. Background is automatically suppressed by a digital filter. Derivative references compensate for small energy calibration and peak width differences between data and references.
B. Sequential Simplex is a non-linear search procedure that determines values for peak intensity, width and position. It does not require reference spectra and is easier to set-up but slower than MLLSQ. Background automatically suppressed by a digital filter.
A. ZAF routine for the analysis of bulk specimens.
B. A standardless routine for the analysis of bulk specimens.
C. A Hall type routine for thin biological and polymer specimens.
D. Thin film analysis based on the Cliff-Lorimer method.
E. The CITZAF program of John Armstrong.
A. Formatted ASCII report of full spectrum information.
B. Popular commercial spread sheet formats.
The display has three parts:
The Menu Bar and the Windows are overlaid by other control windows for the various program procedures. These other control windows are activated by the group of buttons on the left side of the Main Control Window and by selections from the Menu Bar. Up to 10 overlaid spectrum count histograms can be plotted in the Spectrum Display Window. These plots are called WORK, RESULTS and 1 through 8. Spectra can be readily moved among all the plots. All program functions operate on the spectrum in WORK; the results, if any, of a procedure applied to WORK are plotted in RESULTS and other necessary locations.
The remainder of this manual discusses each of the menu items that can be accessed from the Menu Bar, the buttons, and other controls in the Main Control Window, the files created by the program, and other features.
DTSA is a very large computer program (300,000 lines of code) with a wealth of capabilities. Many of the capabilities are so obvious that they require little or no documentation. Other features are not obvious and will test our ability to describe them sensibly. Many of the capabilities are interdependent and intertwined which makes this task even more daunting. The various physical and mathematical processes that are coded into the program represent much of the cumulative knowledge on the subject of x-ray microanalysis gained by the authors and their colleagues at NIST and NIH over many years. Needless to say, we have borrowed heavily from other workers in this field and from the general literature. We are particularly indebted to (in alphabetical order): Brian Andrews, John Armstrong, Mary Carney, Paul Carpenter, Marty Carr, John Colby, Scott Davilla, Kurt Heinrich, David Joy, Janos Labar, Eric Lifshin, John Mansfield, Dale Newbury, Wayne Rasband, Fred Schamber, Walter Schroeder, Gerry Schumacher, Henry Schuman, Peter Statham, Larry Thomas and Scott Wight.
A final, and probably our most important acknowledgment, must go to our several line managers who have been more than a little patient and generous during the long development of this program. These four are, at the NIH, Murray Eden and Henry Eden and, at the NIST, Rance Velapoldi and Eric Steel. We are deeply grateful and appreciative.
DTSA is an on-going project; upgrades of the program and this manual will occur as new capabilities are added. We welcome suggestions for improvements and plead for bug reports.