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Radioactive decay

WE can represent any radioactive decay by an equation.

1- Alpha (α)decay:

alpha decay

 The nucleus of an atom can be represented as: 


  • A = atomic mass (number of protons + neutrons)

  • Z = atomic number (number of protons)

  • X = chemical symbol (as shown on the Periodic Table)

Usually happen in the nuclei of atoms that have atomic number more than 83 

When an alpha particle is emitted from a nucleus the nucleus loses two protons and two neutrons. 

This means the atomic mass number decreases by 4 and the atomic number decreases by 2. 

new element is formed that is two places lower in the Periodic Table than the original element.


Radon decays into polonium when it emits an alpha particle. Here is the equation for that radioactive decay:

2- Beta (β) decay:

When the nucleus of an atom possesses too many neutrons compared to the number of protons it becomes unstable. These are called radioactive isotopes. Unstable nuclei split up in a process called radioactive decay and emit radioactive radiation (β radiation).  For example:

 The chemical properties of the three isotopes are the same but the physical properties are different. 
 Both ordinary hydrogen and deuterium are stable, but tritium is radioactive and decays quite quickly. 
It is a beta emitter.  
In Beta (β-) decay:
1- A neutron changes into a proton plus an electron. 2- The proton stays in the nucleus and the electron leaves the atom with high energy, and we call it a beta particle.

When a beta particle is emitted from the nucleus the nucleus has:one more proton and one less neutron

This means the mass number remains unchanged and the atomic number increases by 1.

Another example:
Carbon-14 is a radioactive isotope of carbon. (It's a carbon atom with 8 neutrons instead of the usual 6.) Here is the equation for the beta decay of carbon-14 into nitrogen.

We can summarize the change in the mass number and atomic number according to alpha and beta decay as shown in the following table:
After alpha or beta decay, nuclei often rearrange themselves. This process causes the loss of energy in the form of gamma rays. There is no effect on either the atomic mass (A) or atomic (Z) numbers.

  3- Gamma decay:

Particle emission often leaves the resulting atom in an excited state. The excited nucleus can emit a gamma ray that carries away the excess energy as electromagnetic radiation. 
Gamma ray emission frequently follows beta decay, alpha decay, and other nuclear decay processes. 
Gamma rays have much higher frequencies than those of light, which means they have a higher energy content.
 Like all forms of electromagnetic radiation, gamma rays move at the speed of light.
Gamma ray emission frequently follows beta decay, alpha decay, and other nuclear decay processes. 
 An example of gamma ray emission occurs when cobalt undergoes beta decay to become nickel. 
The excited nickel gives off  gamma rays in order to drop down to its ground state of energy.