In nuclear physics, beta ecay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. In the case of electron emission, it is referred to as "beta minus" (β−), while in the case of a positron emission as "beta plus" (β+). Kinetic energy of beta particles has continuous spectrum ranging from 0 to maximal available energy (Q), which depends on parent and daughter nuclear states participating in the decay. Typical Q is of order of 1 MeV, but it can be from few keV to few tens MeV. The most energetic beta particles are ultrarelativistic, with speeds very close to the speed of light.