A Computer-Controlled System for Automatically Scanning and Interpreting Photographic Spectra
In analytical spectrography the most time-consuming portion of an analysis is the scanning and interpreting of the photographically-recorded spectra. A system has been devised to shorten this time considerably by using a small digital computer to control the scanning densitometer and subsequently to calculate abundances from the photographic data. The following description applies specifically to spark-source mass spectrography; however, adaptation to other systems would be relatively straightforward. A typical photoplate from our spectrograph contains several thousand lines from as many as 20 graded exposures, and represents approximately 65 elements. Starting with the most intense exposure, the optical transmission of each line is measured using a Grant microphotometer. These transmissions as well as the position of each line are stored in a PDP-8 computer. The computer initiates and completely controls the scanning, and simultaneously converts each line position to an exact mass number from a calibration performed at the beginning of the scan. The computer is programmed to distinguish between lines and empty areas on the photoplate, and all the graded exposures of each line are recorded before the scanning continues to the next line. Backgrounds are continuously upgraded and recorded along with their adjacent line densities. After the desired area of the photoplate has been scanned an emulsion calibration is calculated from the data stored in the computer. Then all line densities on the linear portion of the calibration curve are converted to ionic abundances. Total time involved in scanning 20 exposures on a 15-in. photoplate is now approximately 5 hr.
KeywordsAverage Abundance Photographic Plate Mass Line Cent Transmission Scanning Densitometer
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