Primary count loss

Primary Coincidence. Two or more particles in the measurement zone give rise to two or more overlapping pulses. Depending on their proximity and electrical resolution, these pulses may not be resolved, leading to loss of count. 

Two philosophies have been developed for the fast registration of X-ray absorption spectra [73-76]. One of these can be characterized as a brute-force variant of the normal transmission experiment, where the energy of the primary beam is increased stepwise. It takes about 20-30 min to take a full spectrum, and much of this time is used to perform corrections in the adjustment of the beam and to calm down mechanical vibrations and instabilities, which occur after every movement of the monochromator crystal. The QEXAFS (Quick-Scanning EXAFS) method [75,76] uses a step-wise, rather than a continuous motion of the motors driving the movement of the crystals, so that such extra times are not necessary. If the counting times of the detectors are minimized as well, a full XAFS spectrum of sufficient quahty can be obtained in a few seconds. Spectra with only minor losses in quahty as compared to conventional step-by-step scanning can be obtained in a few minutes. 

The efficiency of the counter measured in this manner will be somewhat in error since the calibration foils are much thicker than the foil discs. This error should be small compared with the error involved in the standard pile flux (10 percent and possibly greater). The selfabsorption of gamma rays in the thick foils will only be about one percent. This is the primary reason for counting gamma rays instead of beta particles. In order to calibrate a counter, a thick foil had to be used to obtain enough activation in the standard pile. If the beta particle s were counted, the self absorption loss would be as high as 20 percent for the gold foil used in the calibration. 

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