MultiPoint Background Counting Times
Note that the MultiPoint background count times are based on the corresponding Hi and Lo Off Peak Times divided by two, although the actual off-peak statistics will vary depending on how many “Iterate Points” are specified for the multi-point background fitting.
For example, let’s suppose that an element is specified to use 200 seconds on-peak counting time and 100 seconds high off-peak and 100 seconds low off-peak. In the case of an element at zero concentration the total integration time on peak and off-peak are normally equal (200 seconds on-peaks equals 200 seconds off-peak) and therefore statistically appropriate (obviously for element concentrations above zero the off-peak count time can be decreased relative to the on-peak counting time).
If the user switches to the MultiPoint background method and the number of points to acquire is say, 4 , then the software will calculate the off-peak acquisition time for each background as 100/2 = 50 seconds each, which yields 400 seconds for the four MultiPoint background measurements on both sides of the peak.
However, if the “Iterate Points” parameter is set to two (for each off-peak side), the MultiPoint background calculation will throw out 2 of those background measurements, so only 2 measurements on each side of the peak will remain in the calculated background. Hence, there will be 4 * 50 seconds or 200 seconds on both sides of the peak background compared to 200 seconds on-peak so the statistics are self-consistent.