Gamma ray

1900 Gamma ray

The book of science

Tom Sharp

Paul Ulrich Villard physics

Gamma ray

Gamma rays

Gamma ray guns

At the time, they didn’t know what these rays were. They didn’t know that alpha rays are helium-4 nuclei; they didn’t know that beta rays are electrons; they didn’t know that gamma rays are, like X-rays, photons. X-rays are emitted by excited electrons; gamma rays were emitted by the decay of nuclei or other particles.

See also in The book of science:

Readings on wikipedia: