Enter the mass before decay (kg) and the mass after decay (kg) into the calculator to determine the Decay Energy. 

Decay Energy Formula

The following equation is used to calculate the Decay Energy. 

E = (M1-M2) * c^2


  • Where E is the Decay Energy (Joules)
  • M1 is the mass before decay (kg) 
  • M2 is the mass after decay (kg) 
  • c is the speed of light (299792458 m/s)

To calculate the decay energy, multiply the total mass decay by the speed of light.

How to Calculate Decay Energy?

The following two example problems outline the steps and information needed in order to calculate the Decay Energy.

Example Problem #1:

  1. First, determine the mass before decay (kg). In this example, the mass before decay (kg) is measured to be 50.
  2. Next, determine the mass after decay (kg). For this problem, the mass after decay (kg) is calculated to be 20.
  3. Finally, calculate the Decay Energy using the formula above: 

E = (M1-M2) * c^2

Inserting the values from above and solving the equation with the imputed values gives: 

E = (50-20) * 299792458^2 = 2.69 e+18 (Joules)


What is decay energy and why is it important?

Decay energy refers to the amount of energy released during the process of radioactive decay, where an unstable atomic nucleus loses energy by emitting radiation. It is important because it helps in understanding nuclear reactions, energy production in nuclear reactors, and the behavior of radioactive materials in medical, industrial, and environmental contexts.

How is the speed of light (c) relevant to calculating decay energy?

The speed of light (c) is crucial in the equation E = (M1-M2) * c^2 for calculating decay energy because it relates mass and energy through Einstein’s theory of relativity. This equation shows that even a small amount of mass can be converted into a large amount of energy, emphasizing the efficiency of nuclear processes in releasing energy.

Can decay energy be harnessed for practical applications?

Yes, decay energy can be harnessed for various practical applications, including nuclear power generation, where the energy released from nuclear fission or fusion is used to produce electricity. It is also utilized in medical treatments, such as in cancer radiotherapy, where radioactive decay is used to target and destroy cancer cells.