I have a dilemma.
In my lab exercise, I was measuring spectra with HPGe detector of several sources (gamma spectroscopy). To determine the energy of the unknown spectrum I first needed to calibrate the detector by making measurements of known elements: Co 60, Cs 137, and Ba 133. The spectra of Co and Cs have nice discernible peaks, and from table I know their energies. For Co ~1332 and 1173 keV peaks, and Cs ~661 keV peak. But I also had Ba 133, and there were 4 peaks, and even tho I have the energies of those peaks (I don't know with 100% certainty that they are correct), when I draw the calibration graph (energy/channel plot), I have some scattering, and my calibration fit is E=a*n+b, where a=($0.78\pm 0.01$) keV, and b=($80\pm 10$) keV.
But if I only take the three distinct peaks (Co and Cs), the calibration parameters are a=($0.8200\pm 0.002$) keV and b=(26.1\pm 0.3)keV. The relative error in this case is minute.
The picture is:
the dark cyan one is fit with all 7 points, and the red dashed is only 3 points.
Now, my dilemma is: do I take more points (I remember from my stat class, that the more the better, since you never know how your data will behave in different regimes), or do I take these three which are totally distinct and I know with 100% the energy of those peaks. And then use that as my calibration?
Is the ~40keV (around 200th channel) difference between these two, a big difference in determining the unknown spectra?
Even tho my relative uncertainty is higher with Barium spectra, maybe it's good to include them, especially if my unknown spectra have peaks on lower energies (channel).
What would you do?
EDIT: Barium spectra:
And my detector has 2048 channels.