Fast Digitizing of Analogue-Recorded Mass Spectra by Means of an X-Y Digitizer Board

摘要

The mass spectra of secondary ions recorded on the X-Y recorder of the ARL ion microprobe mass analyzer (IMMA) consist of a train of narrow peaks or mass lines (as they are more commonly called) spaced at a constant gap width per mass unit interval in the mass range M = 1 to 300 (or sections thereof). The constant spacing is achieved by driving the mass scale (i.e. the X-axis) on the X-Y recorder by the (approximately) squared amplified output of Hall probe which is used to monitor the magnetic field intensity. The exact relationship between Hall signal and mass number has been determined by experiment and used to programme a set of EPROM's in a digital squarer, which assures that the linearity of the mass scale is sufficient for reliable mass line identification by linear interpolation between mass markers. In order to speed up this identification and at the same time obtain the peak height (which is representative of the secondary ion intensity) a computer program has been formulated which permits the digitization of these coordinates (mass number and peak height) from an analogue X-Y recording by use of an X-Y digitizer board. This report explains the procedure, outlines the mathematics and provides a copy of the program as written for an HP 9830 computer together with a sample print-out of results. (Atomindex citation 16:056824)