Nuclear Reactions

Nuclear Fission – Why Does the Sun Shine?

Certain heavy elements in the periodic table have nuclei that spontaneously break apart into pieces – these are the radioactive elements. If you weigh the initial nucleus and then weigh the pieces left after radioactive fission occurs, you will discover something amazing – they don't match.

Radioactive elements can spontaneously decay. We begin with a Uranium^238_92 atom, represented as a ball of green and blue spheres, to show protons and neutrons. An arrow points to the center of figure to indicate that this atom is the initial state. In the final state, we have another ball of green and blue spheres labeled Thorium^234_90, a clump of two green and two blue spheres labeled Helium^4_2, and two purple arrows with arrow bodies being sine waves, each labeled gamma (for gamma-ray). Arrows from the Thorium and Helium atoms point outward to indicate that these are the final states, and the two gamma-rays also point outward.

[NMSU, N. Vogt]

The missing mass in the fission reaction has been converted into energy via the well-known equation

E = mc²

which tells us that Mass and Energy are interchangeable.

Take the mass difference between the initial uranium nucleus and the sum of the final thorium and helium nuclei, multiply by the speed of light squared, and you will find the amount of energy that was converted from mass into energy in the reaction (released in the form of high-energy gamma rays). We can write this as an equation:

E = mc²

where Delta m is the mass difference between the uranium nucleus and the fission product nuclei.

This is a very efficient source of energy. Some fission reactions release as much as 10 Exponent containing the number eighteen ergs/gram of fissionable material.

The problem is that only a small fraction of the Sun is made up of radioactive materials, so the amount of energy released by fission is not sufficient to power the Sun.

Mike Bolte