#8. Nuclear Energy Comes from the Conversion of Mass.

The nucleus of the atom is a dense collection of particles that carries most of the mass of the atom. In nuclear reactions, some of this mass may be converted to energy via Einstein’s famous equation E=mc2 . The chemical identity of the atom depends on the number of positively charged protons in the nucleus, but the nucleus can have different numbers of uncharged neutrons. Nuclei with the same number of protons but different numbers of neutrons are called isotopes of each other.
Most isotopes are unstable, and undergo a process of disintegration known as radioactive decay. The time it takes for half of a group of nuclei to decay is called the half life. Half lives can range from fractions of a second to billions of years. Measuring the number of decays that have occurred in a material allows us to estimate the age of the material.
The decay process can proceed by the emission of alpha particles (two protons and two neutrons), beta particles (fast electrons produced in the nucleus) or gamma rays (high energy electromagnetic radiation).
Energy can be derived from nuclei by fusion (the coming together of small nuclei to form larger ones) or fission (the splitting of large nuclei into smaller ones). In the case where the mass of the final products is less than that of the initial nuclei, the difference is converted into energy as outlined above. Fission energy supplies and appreciable fraction of American electricity, while fusion energy is what powers the sun.

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