Secondary Cosmic-Ray Photons below Cascade Energy

Investigations with small unshielded scintillation crystals carried through the atmosphere by balloons, show large fluxes of photons in the energy region 30 to 300 kev in equilibrium with the primary cosmic ray beam. At 90 g cm^-2 depth the flux is about 22 photons cm^-2 sec^-1 compared with a charged particle flux determined from a Geiger tube of 1. 9 cm^-2 sec^-1 at this same depth. The photon flux at zero depth, taken to be the albedo of this secondary cosmic-ray component, has been estimated by extrapolation to be 8 photons cm^-2 sec^-1 greater than 30 kev.