The apertures were chosen one at a time by simply covering all but one of them with electrical tape. Viewing the output directly to establish a safe input voltage for the PM tube is essential. The anode current must be kept within the tube manufactures safe zone to keep from destroying it. Also as one increases the input voltage to the tube the noise output increases. With this combination the output signal maximum voltage could be amplified up to the maximum input voltage allowed by the MCA board.
Data collection is in itself quite simple.
By observing how quickly the data curve stabilizes, a preset count time can be selected. The curves very rapidly stabilize, in the order of seconds. Count times in the order of minutes are more than adequate. Data was collected for the various spot sizes in three minute intervals. Using the ANSI format for saving the data made it possible to export the data into more powerful mathematical tools like MathCad.