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This discussion on correlation of fluorescent X-ray intensity with concentration is based on data produced under the following experimental conditions. The X-ray tube was operated mainly at 50 peak kv (occasionally at 35) with the d-c tube current ranging from about 5 to 40 ma. The dispersing or diffracting element was a curved mica crystal and the receiver a “thyrode” or multiplechamber Geiger counter. The specimens were usually metallic, although oxide mixtures were used from time to time. The incident beam was directed vertically downward and the specimen held at an angle of 30 deg to the horizontal. Hence, the grazing angle was 60 deg for the incident beam and 30 deg for the fluorescent beam. The specimens were composed of chromium, iron, cobalt, nickel, copper, zinc, and molybdenum, either in the form of commercially pure metal or oxide or binary or ternary mixtures with the concentrations of an element varying from about 10 to 90 per cent. The method of measurement was to read the time, T, with a clock recording directly to 0.01 sec, for the counter to record a fixed number of counts, N, equal to 218 or 262,144. The true counting rates varied from about 50 to 10,000 counts per sec. If a measurement is expressed as a time, T, it will mean the time for the counter to record 218 counts. The intensity of an X-ray spectrum line may be given either as a time, T, or a rate—that is, N/T as counts per second.
Physicist, Philadelphia Naval Shipyard, Philadelphia, Pa.