Gamma radiation does have mass, although it is very small. The mass of a gamma-ray photon is equal to its energy divided by the square of the speed of light. For a gamma-ray photon with an energy of 1 MeV, the mass is approximately 1.1 x 10^-36 kg. This is about 10^-27 times the mass of an electron.

Gamma radiation is not composed of matter in the sense that everyday objects are composed of matter. Gamma rays are pure energy, and they do not have the same properties as ordinary matter, such as mass, volume, or charge. However, gamma-ray photons do have some properties that are similar to those of matter, such as momentum and energy.