Calibration of gamma-ray spectra

[sltungle]

So I have an assignment due in tomorrow night that I've been working on recently and I find myself with a question.

Because our software was playing up it wouldn't give us the correct algebraic relation to calibrate our results, so I've had to manually do this. From the three sources we were investigating in the lab (Na-22, Co-60 and Cs-137) I've taken the 5 real photopeak values that they produce, and the 5 photopeak values that our uncalibrated software gave us, and I've found the straight line that explains them (has an R^2 value of 0.9999904900).

However because of this my data is only really technically calibrated between 511 keV and 1332 keV (because, y'know, interpolation = good, extrapolation = bad), so I was thinking is it mathematically sound for me to take the Ba-137 x-ray with a known energy, and along with the incorrect energy we experimentally obtained plot it against the other 5 values?

This would extend my range of calibration and would remove any negative energy regions from my graph. However I'm worried that, because the mathematics that dictates nuclear structure isn't the same as the mathematics that dictates electron structure (right?) it might be somehow invalid to include the x-ray energy in my calibration.

Thoughts?

 

[jbsteele]

It is generally accepted that including the x-ray energy in your calibration would be acceptable, as long as you are aware of the limitations that may arise from this. It is important to note that although nuclear and electron structure are governed by different mathematics, your calibration should still provide accurate results within the range of your data points. Extrapolation will always carry some degree of uncertainty, regardless of the type of data being used.