Can gamma rays of high enough energy entering our planet's atmosphere reach the surface (50% probability)?
Or, in other words, is there a window for extremely high-energy gamma rays like for the visible spectrum and radio?
This figure, from Electromagnetic Spectrum, shows that the penetration increases with increasing energy, but it seems to level out at about 25 km altitude:
There are no units on the X-axis, and thus it does not show the energy for the highest energy gamma rays for this figure. This does not rule out a window at even higher energies.