Counting interval

The best precision attainable with present apparatus for reasonable counting intervals should correspond to a standard deviation near 0.02% for a major constituent in an ideal sample properly handled. In most x-ray emission spectrography, the standard deviation is 1% or greater. Much of this discrepancy must be traceable to the way in which samples are prepared, and handled in the spectrograph, manipulation of the... 

The first subdivision is most frequently met with in the determination of major constituents (7.11). An extreme example is the counting of an analytical line for a pure metal when At may be 105 counts and Atb only 50 over the same short counting interval so that Nt — Nb, which measures the intensity of the analytical-line, is sensibly identical with At-... 

Table 8-2 contains unpublished results fron the authors laboratory that illustrate the effectiveness of pulse-height selection in the determination of light elements. In the case of silicon, the background was due mainly to scattered x-rays. In the case of sulfur, multiplier phototube noise was also present. The counting interval was 10 seconds for Nt (total count) and for Nb (background). The excellent results for sulfur could not have been obtained had there not been careful and fortunate selection of the multiplier phototube. 

Note that Nb may be approximated as the product of At and a counting rate measured for the background over a different counting interval for example, over an interval longer than At if one wishes to establish the background with greater precision. Whether such higher precision is worth while depends upon the relative contribution of A7b in Equation 10-12. 

The experiments of this section were kindly carried out for the authors by Dr. W. F. Loranger, X-ray Department, General Electric Company, Milwaukee, Wise., on a General Electric XRD-5 D/S spectrograph with SPG-4 detector. Analytical lines, iron K counting interval 40 seconds approximate counting rate, 40,000 counts per second. 

The I s represent the counts obtained in the counting interval (minutes) given in brackets, and V and n are the pump flowrate and the counter efficiency, respectively. 

Slightly overestimated due to modified counting interval in order to enable counting within the allowed working period. 

NEUTRON FLUX INTERVAL COUNT INTERVAL INSTRUMENTATION ELEMENTS DETERMINED... 

Table II summarizes the parameters which relate to the measurement of each element neutron activation products, half-lives, y-ray energies, lengths of irradiation, decay, and counting. Also listed are the possible interfering radionuclides and interfering reactions producing the same isotopes from another element which were necessarily evaluated. This table is subdivided into three sections representing the elements determined during each of the three counting intervals.

It is anticipated that more experimentation using longer counting intervals will reduce the spread of replicate measures even more. However, it is not... 

Because the system was set up with a diverter valve as shown in Figure 9.2, samples could be processed onto the column and washed, with solutions going to waste, while the previous sample was stopped in the detector for counting. On completion of the counting interval, the detector flow cell could be washed, and then the sample already processed and separated on the column could be eluted to the detector. Using a count time of 15 minutes, the analysis time was 40 minutes for the first sample and 20 minutes for each subsequent sample or blank. 

Figure 6. Effect of counting interval on UC peak (Porasil A, 2.8 mm X 1000 mm...

Figure 3-20 Resonance Raman spectra of TCNQ and electrogenerated TCNQ--. [TCNQJ 1.09 mM, laser power = 20 mW, bandpass = 1.2cm-1 [TCNQ ] = 2.24 mM, laser power =74 mW, bandpass = 2.2cm 1. TCNQ - was electrogenerated by controlled potential caulome-try at -0.10 V vs. SCE in 0.1 M TBAP/CH3CN. All spectra were scanned at 50 cm 1 min-1 using a 1.00 s counting interval. Plasma lines were removed at 4579 A with an interference filter and at 6471 A with a Claassen filter. S denotes a normal Raman band of the solvent (acetonitrile). No normal Raman bands are observed for the supporting electrolyte (TBAP, tetrabutylammo-nium perchlorate). (Reproduced with permission from Ref. 75. Copyright 1976 American Chemical Society.)...

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