Alpha Radiation as a Helium Nucleus, Beta Radiation as a High Energy Nucleon and Gamma Radiation as Electromagnetic

Alpha radiation, often symbolised as α, is effectively a Helium nucleus. This means it consists of two protons and two neutrons, providing it with a +2 charge.
Owing to their relative size and charge, α particles interact strongly with matter and cannot penetrate very far. A few centimetres in air or a thin sheet of paper can easily stop them.
Upon emission from an atom, α particles cause the atomic number to reduce by 2 and atomic mass by 4 due to loss of two protons and two neutrons respectively.
Beta radiation, often symbolised as β, is essentially a high-energy electron or positron. They are referred to as high-energy electrons or positrons because they move at speeds approaching the speed of light.
β particles are smaller and have less charge than α particles, allowing them to penetrate further into materials. A few centimetres into aluminium or a metre into the air can stop them.
A β particle is formed within the nucleus when a neutron is converted into a proton, causing the atomic number to increase by 1. No change in atomic mass occurs.
Gamma radiation, often symbolised as γ, are electromagnetic waves. They carry no charge and, unlike α and β particles, are not particle radiation.
With much shorter wavelength, γ waves are far more penetrative than either α or β particles. They can pass through several centimetres of lead or several metres of concrete before being stopped.
γ radiation usually accompanies α or β radiation as excess energy from the radioactive nuclei is released.
Despite having no charge or mass, γ waves are capable of ionisation. This is due to their high energy, allowing them to knock off tightly bound electrons from their parent atom.
Unlike α and β radiation, γ radiation does not alter the atomic number or mass of the atom from which it is emitted.