Why do gamma rays ionise, but not photons?

Gamma rays are electromagnetic radiation with an energy level above a specified amount / wavelength shorter than a specified amount. Gamma rays, like all electromagnetic radiation, exists as a photon. A Gamma ray is a photon with the highest level of energy. read more

Certainly not. There is a very wide range of energies for gamma photons. They start with an overlap with hard X-rays, but there is no upper limit: every now and then we get a gamma ray with such high energy, no nuclear reaction could create it: it is assumed it is created from some stellar phenomenon, but the exact source is still an open question. read more

It was more penetrating than the most energetic gamma rays, but like gamma rays, the radiation was composed of electrically neutral particles so that it did not ionise atoms as it passed through matter. read more