Abstract: A method and apparatus for measuring a neutron flux in which the neutrons induce fission reactions in the layer of fissile material, the fission reactions in turn inducing light pulses in a scintillator material. A photomultiplier tube detects the light pulses and emits an electrical pulse in response. The electrical pulses are summed, checked for coincidence, stored, and otherwise manipulated in order to detect and measure neutron flux. In one advantageous embodiment of the invention, several different fissile materials or coated and uncoated fissile materials are used in order to obtain a spectral distribution of the incident neutron flux. At another embodiment, opposed detectors are used in order to discriminate between actual neutron-induced fission events and background events.