UNIV CALIF BERKELEY,SPACE SCI LAB,BERKELEY,CA 94720
; UNIV CALIF BERKELEY,DIV NUCL SCI,BERKELEY,CA 94720
; ACAD SINICA,INST HIGH ENERGY PHYS,BEIJING 100039,PEOPLES R CHINA
; IST NAZL FIS NUCL,LAB NAZL GRAN SASSO,I-67010 ASSERGI,ITALY
An upper limit to the diffuse cosmic ultrahigh-energy (UHE) gamma-spectrum from 5 TeV up to 1 PeV is inferred from data on the spectrum of the electromagnetic component of secondary cosmic rays recorded by emulsion-chamber experiments at various atmospheric depths. Our Monte Carlo simulation of the atmospheric propagation and interaction of the photons and protons with primary energies of (5 x 10(12))-10(15) eV shows that the intensity of uncorrelated gamma events with visible energies E-gamma = 5-100 TeV observed in emulsion-chamber experiments is sensitive to the diffuse cosmic UHE gamma-rays at the level of approximately 10(-3) compared to primary cosmic rays in the same energy region. We also discuss the relevance of the UHE gamma-spectrum to topics such as diffuse photons as by-products of the energy loss of extragalactic cosmic rays interacting with the cosmic 2.7 K background radiation, direct photons as a result of possible new production mechanisms, and photons as products of radiative decay of unstable cosmological relic neutrinos of mass approximately 5 TeV-1 PeV.