Nuclear fusion occurs when light nuclei are forced together to produce heavier nuclei. What byproduct is commonly formed?

• A. A reaction that produces energy by splitting a heavy nucleus into lighter nuclei.
• B. A reaction that occurs when light nuclei are forced together to produce heavier nuclei; hydrogen is the byproduct.
• C. A reaction that occurs when light nuclei are forced together to produce heavier nuclei; helium is byproduct.
• D. The emission of an electron from a nucleus during beta decay.

Answer: (C)

When light nuclei fuse, they form a heavier nucleus with a higher binding energy per nucleon, releasing energy in the process. The most common heavier product from such fusion is a helium nucleus (helium-4). For example, deuterium and tritium fusion produces helium-4 along with a neutron and energy. Hydrogen itself isn’t the byproduct because the reactants are light hydrogen isotopes that combine to make helium. This fusion scenario is different from fission, which splits a heavy nucleus, and from beta decay, which emits an electron. So helium is the commonly formed byproduct.