Nature of β-particles : A β-particle is an electron or a positron.
Properties of β-particles :
1. β-particles have a moderate ionizing power. It is about 100 times less than that of α-particles, but 100 times more than that of γ-rays.
2. They have a moderate penetrating power. It is about 100 times more than that of α-particles, but 100 times less than that of γ-rays.
3. They are deflected by electric and magnetic fields. Their deflection is more than the deflection of α-particles in the same field but in the opposite direction.
4. They affect photographic plates.
5. They cause fluorescence in a fluorescent material such as zinc sulphide.
6. Their energies and speeds are very high. Their speed is of the order of 10 m/s. Some β-particles have speeds of the order of 0.99 c, where c is the speed of light in free space.
7. They cause more biological damage than α-particles, because they have more penetrating power.
[Note : When a nucleus emits an electron, one of its neutrons changes to a proton; the electron is accompanied by a neutral and almost massless particle called antineutrino \(\vec v_e\) with which the electron shares its energy and momentum. Hence, β-particles are emitted with speeds ranging from about 0 to 0.99 c
The properties of a positron are identical to those of an electron except that it carries a positive charge of the same magnitude as an electron. A positron emission in a β+ decay is accompanied by a neutrino ve. A positron is an anti-particle of an electron, and an antineutrino is an antiparticle of neutrino.
The existence of a small neutral particle, emitted simultaneously with the electron in β -decay, was proposed in 1931 by Wolfgang Pauli (1900 -1958), Austrian-US theoretical physicist. It was confirmed experimentally in 1956 by Frederic Reines and Clyde Lorrain Cowan, Jr., US physicists. This neutral particle, that appears in β+ -decay, was called the neutrino. It travels with a speed very close to that of light in free space. The existence of positron (in 1928) and other antiparticles was predicted by Paul Adrien Maurice Dirac (1902 – 84), British theoretical physicist. All these predictions were eventually confirmed experimentally; the positron was discovered in 1932 by Carl David Anderson, US physicist.]
