A method for inferring incident count rates of electromagnetic energy at a detector is provided. In one embodiment, the method includes transmitting electromagnetic radiation through a fluid and receiving a portion of the electromagnetic radiation at a detector. The method also includes measuring the energy spectrum of the portion of the electromagnetic radiation received by the detector and using the measured energy spectrum and a physical model of detector response to electromagnetic radiation to infer incident count rates for discrete energy levels of the portion of the electromagnetic radiation received by the detector. Additional systems, devices, and methods are also disclosed.