Eppley Institute for Cancer Research

University of Nebraska Medical Center

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Background Calculation

There are two areas were BEAM-ish performs a background calculation.  By far the more reliable measurement comes from the Fit Manager due to the complicated analysis it performs.  In general the number originating from PEAKSTATS should provide a reasonable estimate.

Within Peakstats

The calculation within PEAKSTATS it carried out as the average of all integrated intensities within the entire reflection.  For small reflections (those existing on less than 100 images out of 1000),  the average will be close to the background due to the large number of measurements of background in the average.  This measured value will always be slightly greater than the actual background due to the inclusion of the peak in the calculation.  Its advantages with in PEAKSTATS are that it is fast, simple, and will always result in a value.

Within Fit Manager

The best estimates of the back ground are available within the Fit Manager.  This is because the calculation removes the peak from the background estimate.  The downside is that it only looks in a relatively small window about the peak.  There are two variations available.  The first is the calculation of a constant.  The second is a linear background.  These options are available with either the Differential Evolution Genetic Algorithm or the Levenburg-Marquette Method for performing Gaussian fitting.