Introduction to Understanding Neutron Sources

Female hands holding an enlarged atom

Neutron sources are devices or elements that emit neutrons—the neutrally charged subatomic particles that, together with protons, make up the atomic nucleus. Neutron sources have a number of applications in varied fields, such as physics, engineering, medicine, petroleum exploration, biology, chemistry, and nuclear power. They come in a variety of shapes and sizes, depending on purpose and application.

Neutron sources emit neutrons via one of two methods. The first is fission, which involves the splitting of the neutrons away from the nucleus. Uranium, a highly unstable element, is implemented in this process. It absorbs neutrons from other atoms, and after the absorption it promptly splits into two smaller waste atoms, while releasing one to three neutrons at the same time.

The other method of releasing neutrons is spallation. This involves firing a concentrated proton beam into a neutron-rich element, such as lead, which causes some neutrons to tear away from their nuclei. In short, the difference between fission and spallation can be likened to the difference between luring the neutrons out of their respective atoms, versus blowing them out of the water.

Types of Neutron Sources

There are three main types of neutron sources, with sizes ranging from large to subatomic.

Nuclear reactors

A nuclear reactor uses nuclear fission to create power. It is composed of a reactor core of nuclear fuel, a neutron moderator that regulates the speed of splitting neutrons and maintains a stable nuclear chain reaction, as well as other control mechanisms such as control rods, which sustain the rate of the reaction. A typical nuclear power plant would function something like this: the fission of neutrons generates heat, which when applied to a water source produces steam. This steady flow of steam is directed into a turbine. As the steam causes the turbine to rotate, the generator then turns, producing electricity. The electrical current is then directed to transformers to provide the correct voltage to end users.

Particle accelerators

These circular and circuitous machines use electromagnetism to guide high-velocity charged particles along a predetermined path within a vacuum, in order to collide them into atoms. The atoms then break into smaller particles; the manner and composition of the breakage reveals insights about the targeted elements. The speed of these accelerated particles can sometimes approach the speed of light. These machines consist of a particle source, a beam pipe, electromagnetic equipment to guide the particle beam along the circuit, the targets themselves, and detectors.

Spontaneous fission

This is a type of radioactive decay that is rare, but can be harnessed to produce vast amounts of energy. It occurs in heavy elements such as uranium, plutonium, and californium. The atoms of these unstable elements periodically split into two, releasing energy in the process. That energy, in turn, can be harnessed by a nuclear reactor in the same way that the energy from other nuclear energy types is harnessed. The element of Californium-252 is commonly used as a neutron source.

What Can Neutron Sources Be Used For?

Nuclear reactors are used to conduct research in fields such as physics, chemistry, biology, and medicine. Nuclear power plants generate electricity for thousands of people worldwide. There are many advantages that nuclear power enjoys compared to more traditional energy sources, such as cleaner energy without releasing greenhouse gases, cost-efficiency, and availability.

Particle accelerators allow scientists to explore what holds atoms together and gain insights into the fabric of the physical universe. They also have practical applications in diagnosing and treating cancer, sterilizing equipment, finding oil, fossil fuels, and minerals in the earth, and processing computer chips.

Spontaneous fission, such as by Californium-252 (or CF-252) can allow nuclear plant workers to more closely monitor their reactors, and thus start up and shut down as needed. In addition, CF-252 has been used in military applications, in metal detectors, and for oil and metal analysis.

Neutron sources are a powerful asset in the scientific and industrial fields and have much potential for further implementation in the future.

Image Credit: Natali_ Mis / Shutterstock.com

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