In this chapter, we discuss photonic, single-transient radiation sensors that use optical fibers to transmit signals to a remote location. Our discussion deals with sensors for gamma rays, x rays, and neutrons. Gamma rays and x rays are both electromagnetic waves, but they have different energies and thus different penetration depths. This difference in energy necessitates the use of a different type of sensor for each type of wave. Likewise, neutrons are particles that have varying energies, so the absorption of energy as a function of depth in a material is important in designing sensor systems.