The Collaborative International Dictionary
Electron \E*lec"tron\, n. [NL., fr. Gr. 'h`lektron. See Electric.]
Amber; also, the alloy of gold and silver, called electrum. [archaic]
(Physics & Chem.) one of the fundamental subatomic particles, having a negative charge and about one thousandth the mass of a hydrogen atom. The electron carries (or is) a natural unit of negative electricity, equal to
4 x 10^ -10 electrostatic units, and is classed by physicists as a lepton. Its mass is practically constant at the lesser speeds, but increases due to relativistic effects as the velocity approaches that of light. Electrons are all of one kind, so far as is known. Thus far, no structure has been detected within an electron, and it is probably one of the ultimate composite constituents of all matter. An atom or group of atoms from which an electron has been detached has a positive charge and is called a cation. Electrons are projected from the cathode of vacuum tubes (including television picture tubes) as cathode rays and from radioactive substances as the beta rays. Previously also referred to as corpuscle, an obsolete term. The motion of electrons through metallic conductors is observed as an electric current. A particle identical to the electron in mass and most other respects, but having a positive instead of a negative charge, is called a positron, or antielectron
Usage examples of "beta rays".
That had been preceded by the discovery of radio waves and cathode rays, and it was to be rapidly followed by the discovery of alpha rays, beta rays, and gamma rays.
Radio waves and visible light were clearly waves, while cathode rays, alpha rays, and beta rays were streams of speeding particles.
One could of course argue that the suit offered protection against beta rays, that, while it may indeed have impeded movement, at the same time -- being transparent -- it allowed one to see well, etc.
They were fortunate also that most of the radiation from the particles here came as beta rays, rather than the more insidious neutrons.