Transformation of Elements

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 ⁰-1^e + 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 ⁰-1^e + ²³⁰₉₀Th + energy

↑           ↑

2α-particles 2β-particles

Thorium-234 decays by emitting a β-particle to the element Protactinium-234 thus:

²³⁴₉₀ Th→ ⁰-1^e _­+ ²³⁴₉₁Pa + energy

Generally we represent alpha (α) decay by

^A_BX→⁴₂He + ^(A-4)_(z-2)Y

↑

α-particle

and Beta (β)-decay by ^A_ZX→ ⁰-1^e _­+ ^A_(Z+1)Y

↑

Β-particle

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.