# Why does gamma radiation have a low ionising ability?

Why does gamma radiation have a low ionising ability?
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Brendon Melton
Why do gamma radiation does not have a high ionising ability.
This isn't true. Gamma rays have energies of $\gtrsim 100$ keV, which is orders of magnitude higher than the energy required to ionize matter. They are ionizing radiation.
You may be misunderstanding something you've heard about the fact that some gamma rays are highly penetrating. Gamma rays interact with matter via the photoelectric effect, Compton scattering, and pair production. Each of these processes has some probability, which depends on the energy of the gamma, and also, for some of these processes, on the atomic number of the atom. Low-energy gammas, bordering on the x-ray region, are relatively non-penetrating, but higher-energy gammas will typically pass through a fairly large amount of matter without interacting. For example, one might use a lead brick as shielding against high-energy gammas. So in this sense, high-energy gammas may be relatively unlikely to produce ionization in a given object, if the object is not very thick and has a low atomic number.