The dictionary defines fission as “a splitting or breaking up into parts,” while fusion is “a merging of separate elements into a unified whole.”

As relates to nuclear physics, both are reactions that produce energy. Simply put, fission is the dividing or splitting of the nucleus of an atom, and fusion is the process of joining together of two nuclei. They are very opposite processes, but the amount of energy released is enormously different.

In 1939, scientists set about to prove Einstein’s theory that mass could be converted into energy, expressed in the formula, E = mc 2, where E represents units of energy, m represents units of mass, and c 2 is the speed of light squared. Since the speed of light is a very large number (186,000 miles per second) and is multiplied by itself, this equation predicted that a small amount of heavy matter can be converted in a nuclear reaction that would release a huge amount of energy.

In 1940, fission was accomplished in the first nuclear reactor, proving Einstein correct, and the Atomic Age was born.

In a nuclear reaction, neutrons are shot at high velocity at uranium-235 nuclei. When a neutron hits a nucleus, the U-235 becomes U-236. This form of uranium is unstable and wants to split apart. When it splits (fission), it gives off three neutrons and large amounts of energy in the form of heat. Those neutrons hit three other U atoms, and they become U-236. So, each time that happens, and it’s almost instantaneous, the reaction gets three times larger. That process, once started, continues by itself until fuel exhaustion and is called a chain reaction.

Uncontrolled, the reaction causes a huge sudden release of heat resulting in an explosion. This “atomic bomb” is what essentially ended World War II when it was dropped on Japan. The yield from such a device is normally measured in kilotons (thousands of tons) of TNT.

In nuclear reactors used for peaceful purposes like in a power plant or a submarine, the process is controlled using rods that contain a neutron absorbing material. Inserting the rods slows the fission reaction and drawing them out speeds it up. The heat from the reaction is used to make steam which spins a turbine. When connected to a generator, electricity is made, or when connected to a shaft, can propel a ship as large as an aircraft carrier.

Fusion, on the other hand, is just the opposite of fission. Instead of splitting atoms, the process joins atoms like hydrogen together to make helium. In nature, stars like our sun perpetuate due to nuclear fusion. The energy released from nuclear fusion reactions account for the heat and longevity of the sun and other stars. The fusion of nuclei in a star provides that energy and synthesizes new nuclei as a byproduct of the fusion process.

On Earth, we have been able to produce nuclear fusion artificially. The first time was in 1952, when a hydrogen bomb, also known as a thermonuclear device, was detonated by the United States on a remote island in the South Pacific. The yield of this type weapon is measured in megatons (millions of tons) of TNT.

Some of the early scientists working on a fusion bomb objected on the basis that it would provoke a nuclear arms race, which is exactly what happened. As of now, there are five or more nations besides the United States that have tested an H-bomb. Most recently, North Korea claimed to have done so, but that has not been confirmed.

The hydrogen bomb gets its name from the isotopes of hydrogen, deuterium and tritium, which, when fused, make helium atoms. Extreme high pressure and temperature are required for the fusion process. In order to achieve this inside the bomb, a fission explosion must happen first to trigger the fusion.

There have been many studies and small experiments trying to find ways to safely contain a fusion reaction for peaceful uses such as power generation. So far, although there has been progress, it has not been shown to be economically feasible.

However, on the peaceful side, nuclear fission reactors produce radioactive isotopes used for cancer and other medical condition treatments. A radioisotope is a different form of an atom of the same element. Both have identical properties, but different relative atomic masses. While the number of protons is the same, the number of neutrons in the nucleus is different which produces small amounts of medical radiation.

According to the World Nuclear Association, “Scientists continue to find new and beneficial ways of using nuclear technology to improve our lives. In our daily life we need food, water and good health. Radioisotopes play an important part in technologies that provide us with these basic needs. The United Nations’ International Atomic Energy Agency is a base for international cooperation in hundreds of development projects.”

The technology that started out to be a race to acquire a weapon of mass destruction could prove to be very beneficial to humankind.

Those who would like to ask me questions about any other science topic may e-mail inquiries to

Marcus Goodkind of Tuckasegee, a retired aerospace engineer, worked with the National Aeronautics and Space Administration as a manager at Kennedy Space Center on all the manned programs from Mercury to Shuttle, including Apollo 11, the first manned lunar landing.