抄録
It is pointed out that balloon observations so far reported on the finite flux of diffuse cosmic X-rays with energies greater than 0.2 MeV are subject to the procedure of subtracting the contribution of atmospheric X-rays.
The transport of photons generated in the atmosphere was followed by a Monte Carlo calculation. It is found that energy-degraded photons generated at greater depths cause a build-up effect and flatten the intensity vs depth relation, the growth curve, of omnidirectional atmospheric X-rays at depths smaller than 10 gcm−2. The present calculation can explain the behaviour of the observed growth curves. Thus, it is concluded that the assumption, adopted in some of the reports, that the growth curve is represented by a power function of the atmospheric depth is not valid. The present result demonstrates that the observations thus far have given only an upper limit of the cosmic X-rays flux above 0.2 MeV.
