There are two types of radioactivity – natural and artificial radioactivity.
The phenomenon of radioactivity was first discovered by Henri Becquerel
Natural radioactivity is the spontaneous disintegration of the nucleus of an atom during which α-particle or β-particle, or gamma rays or a combination of any or all the three and heat (or energy) are released.
When a radioactivity element undergoes radioactive decay, it may emit either α-particle, β-particle or γ rays. This changes the atomic number of the element, hence a new element is formed. For example, Radium-226 decays by emitting an α-particles to turn into a new element Radon. Radium-226 has a mass number 226 and an atomic number 88 and hence it is denoted by 22688Ra. The α-particles it emits is a Helium nucleus denoted by 42He. So when Radium 226 emits an α-particle. We can write a nuclear equation:
22688Ra → 42He + 22286Rn + energy
(Radon – 222)
Radon – 222 decays to Radium – 222 by emitting 2 β-particles. When the nucleus of an atom emits a β-particle (i.e. an electron), the atomic number of the atom increases by one unit, but its mass number remains unaltered. Hence since two β-particles are emitted from Radon 222 we can write the equation
22286Rn → 2 0-1e + 22288 Ra + energy
Uranium-238 decays by emitting two α-particles and two β-particles to thorium -230. Hence we can write the nuclear equation thus:
23892U → 2 42H + 2 0-1e + 23090Th + energy
Thorium-234 decays by emitting a β-particle to the element Protactinium-234 thus:
23490 Th→ 0-1e + 23491Pa + energy
Generally we represent alpha (α) decay by
ABX→42He + (A-4)(z-2)Y
and Beta (β)-decay by AZX→ 0-1e + A(Z+1)Y
Gamma radiation (γ) is a form of light, emitted as photons of energy hf, and has zero mass number and zero charge (A = 0, Z = 0).
To balance a nuclear equation we ensure that the sun of the atomic numbers, Z (subscripts) must be the same on the two sides of the equation. Also the sum of the mass numbers A (superscripts) must be the same on the two sides of the equation.