A Measurement of the Air Fluorescence Yield

We measured the air uorescence yield as a function of pressure with electrons between 1.4 MeV and 1000 MeV by means of a 90 Sr source and an electron beam. Results indicate that the uorescence yield is proportional to electron energy loss from 1.4 MeV to 1000 MeV. The dE dx relativistic rise in air is detected. We describe the pressure temperature dependency of air uorescence by a formula derived from simple kinetic theory. With the aid of the 1966 US Mid-latitude Standard Atmospheric Model, we calculate the altitude dependence of uorescence yield of an 80 MeV electron which demonstrates how this measurement could improve the longitudinal particle density prole determination of extensive air showers (EAS) observed by detectors such as the High Resolution Fly's Eye and the Telescope Array.