According to Rutherfordâ€™s experiment, a sample of radioactive substance is put in a lead box and is allowed to emit radiation through a small hole only. When the radiation enters into the external electric field, it splits into three parts: Î±-rays, Î²-rays, and Î³-rays.

# Î±-decay

Nearly 90% of the 2500 known nuclides are radioactive; they are not stable but decay into other nuclides
• When unstable nuclides decay into different nuclides, they usually emit alpha (Î±) or beta (Î²) particles.
• Alpha emission occurs principally with nuclei that are too large to be stable. When a nucleus emits an alpha particle, its N and Z values each decrease by two and A decreases by four.
• Alpha decay is possible whenever the mass of the original neutral atom is greater than the sum of the masses of the final neutral atom and the neutral helium-atom.

# Î²-decay

There are different simple type of Î²-decay: Î² â€“, Î²+, and electron capture.
• A beta minus particle (Î²+) is an electron. The emission of Î² â€“ involves transformation of a neutron into a proton, an electron, and a third particle called an antineutrino (v).
• Î² â€“ decay usually occurs with nuclides for which the neutron to proton ratio (N/Z ratio) is too large for stability.
• In Î² â€“ decay, N decreases by one, Z increases by one and A does not change.
• Î² â€“ decay can occur whenever the neutral atomic mass of the original atom is larger than that of the final atom.
• Nuclides for which N/Z is too small for stability can emit a positron, the electronâ€™s antiparticle, which is identical to the electron but with positive charge. The basic process called beta plus Î²+ decay.

p â†’ n + Î²+ + v (Î½ = neutrino)
• Î²+ decay can occur whenever the neutral atomic mass of the original atom is at least two electron masses larger than that of the final atom
• The mass of v and v is zero. The spin of both is 1/2 in units of h/2Ï€. The charge on both is zero. The spin of neutrino is antiparallel to its momentum while that of antineutrino is parallel to its momentum.
• There are a few nuclides for which Î²+ emission is not energetically possible but in which an orbital electron (usually in the k-shell) can combine with a proton in the nucleus to form a neutron and a neutrino. The neutron remains in the nucleus and the neutrino is emitted.

p + Î²+ â†’ n + v

# Î³-decay

The energy of internal motion of a nucleus is quantized. A typical nucleus has a set of allowed energy levels, including a ground state (state of lowest energy) and several excited states. Because of the great strength of nuclear interactions, excitation energies of nuclei are typically of the order of 1 MeV, compared with a few eV for atomic energy levels. In ordinary physical and chemical transformations the nucleus always remains in its ground state. When a nucleus is placed in an excited state, either by bombardment with high-energy particles or by a radioactive transformation, it can decay to the ground state by emission of one or more photons called gamma rays or gamma-ray photons, with typical energies of 10 keV to 5 MeV. This process is called gamma (Î³) decay.

All the known conservation laws are obeyed in Î³-decay. The intensity of Î³-decay after passing through x thickness of a material is given by I = I0eâ€“Î¼x (Î¼ = absorption co-efficient).