What does The Energy Response Graph mean? Posted on April 18, 2018May 7, 2018 The Energy Response Graph shown in the operation manual gauges how the instrument will respond to various energies. GM detectors cannot distinguish different types of energies, but we can gauge how the detector responds to them. For example, on the graph shown above, the Sidewall response starts at 50 keV with a relative count rate of 1. This means that an isotope giving off radiation at 50 keV will have a relative response of 1, giving an accurate reading of the radiation present. However, if you notice that at its highest peak, 80 keV, the unit may over respond almost 3 times. This means that if an isotope is emitting radiation at 80 keV, the detector may be reading that there is three times the exposure present than is actually present. The Ranger will again start to have a relative response of 1 at about 230 keV.