Counting rate corrections

Average net beta-particle count rate corrected for 234Th decay between separation from uranium and counting ... 

Figure 6 a Chemical composition of raw source, as determined by HPLC separation the count rate corrected for decay to the end of bombardment b Chemical composition of purined source, as determined by HPLC separation the count rate corrected for decay to the end of bombardment,... 

Wire Segment Start Time Counting Rate Corrected Counting Rate Wire Segment Start T ime Counting Rate Corrected Counting Rate... 

Such significant increase of accuracy may be explained on the base of analysis of the numerical values of the theoretical correction coefficients and calculated for 1, , and for analytical pai ameter lQ.j,yipj.j,jj- Changing from lines intensities for the ratios of analytical element line intensity to the intensity of the line most effecting the result of analytical element (chromium in this case) measurement enables the decreases of the error 5 or even 10 times practically to the level of statistics of the count rate. In case of chromium the influencing elements will be titanium, tungsten or molybdenum. 

In Equation 6-1, Io/I, usually an intensity ratio, is the quotient of the corrected average counting rate for the exposed substrate by that for the substrate covered with d cm of iron foil. The mass absorption coefficients of iron are m, a mean value for the incident (polychromatic) beam and g2, for the characteristic line being counted. The angles d and 02 are those made with the sample by the incident beam (30°) and by the emergent beam (60°), the beams being regarded as rays and... 

The corrected counting rates used in these calculations were the means of four readings. 

Convert the readings in Data Table 2 to a count rate in cpm by multiplying them by 2. Subtract the background radiation rate obtained in step 2 from each count rate to obtain the corrected count rate. 

Time (min) Counts Count rate (cpm) Corrected count rate (cpm) Time (min) Counts Count rate (cpm) Corrected count rate (cpm)... 

To determine the expressions for the optimised counting times, we write the expressions (10) and (11) in terms of count-rates and times (count rates are constant quantities for each Bragg reflection). We assume that the incident neutron flux is constant during a flipping ratio measurement, and that no dead-time correction is needed. In these conditions, we have the relations ... 

Also important is the effect of detector dead time. When ions are detected using a pulse counting (PC) detector, the resultant electronic pulses are approximately 10 ns long. During and after each pulse there is a period of time during which the detector is effectively dead (i.e. it cannot detect any ions). The dead time is made up of the time for each pulse and recovery time for the detector and associated electronics. Typical dead times vary between 20 and 100 ns. If dead time is not taken into account there will be an apparent reduction in the number of pulses at high count rates, which would cause an inaccuracy in the measurement of isotope ratios when abundances differ markedly. However, a correction can be applied as follows ... 

If no dead time correction is applied, then a linear calibration would not be possible, since the higher count rates between 10 and 10 Hz would be underestimated. This provides a way of determining the dead time empirically, i.e. by re-integrating the isotopic signals with different dead times until a linear calibration is obtained for a series of accurately known standards. 

Another limit source of uncertainty in isotope ratio measurements by mass spectrometry is the dead time of the ion detector for counting rates higher than 106cps, because a lower number of counts are usually registered than actually occur. Dead time correction of the detector is required if extreme isotope ratios are measured by channel electron multipliers and pulsed counting systems.86... 

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