[W/K] :: beta rays

  Beta rays \Be"ta rays\ (Physics)
     a form of ionizing radiation emitted by radioactive
     substances (such as radium), more penetrating than alpha
     rays, and consisting of negatively charged electrons. The
     electrons are the same kind of particle as those of cathode
     rays, but have much higher velocities (about 35,000 to
     180,000 miles per second). They are readily deflected by a
     magnetic or electric field.
     [Webster 1913 Suppl.]

  Electron \E*lec"tron\, n. [NL., fr. Gr. 'h`lektron. See
     Electric.]
     1. Amber; also, the alloy of gold and silver, called
        electrum. [archaic]
        [1913 Webster]
  
     2. (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 3.4 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
        [Webster 1913 Suppl. +PJC] Electro-negative