New measurement on photon yields from air and the application to the energy estimation of primary cosmic rays

The air fluorescence technique is used to detect ultrahigh-energy cosmic rays (UHECR), and to estimate their energy. Of fundamental importance is the photon yield due to excitation by electrons, in air of various densities and temperatures. After our previous report, the experiment has been continued using a 90Sr β source to study the pressure dependence of photon yields for radiation in nitrogen and dry air. The photon yields in 15 wave bands between 300 nm and 430 nm have been determined. The total photon yield between 300 nm and 406 nm (used in most experiments) in air excited by a 0.85 MeV electron is 3.81 ± 0.13 (±13% systematics) photons per meter at 1013 hPa and 20 °C. The air density and temperature dependencies of 15 wave bands are given for application to UHECR observations.