i am calibrating a detector set up using alpha particles to find resolution. i have 2 silicon detectors a thin and thick one where the alpha is expected to pass through and lose energy in the first and be stopped by the second. My handbook says i can find the energy resolution in the second thicker detector by using the standard FWHM/centroid and times this by alpha particle energy 5157KeV to get KeV resolution. then i can just take measurements from the face (front or back) of the detector with best resolution. This i understand. But, for the first detector it is saying to plot a difference in the energy between the front and back face measurement, of which the width of this peak is the resolution of the detector. this i dont get at we generally choose a face to measure from in the actual experiment. why is there two different methods? is it because the particles pass through the first detector and because it has a thickness (in order to slow down the particle) there will be an energy difference between front and back?