Neutron (noun, “NOO-trahn”)
A neutron is a particle with neutral electric charge. That is, it’s neither positively nor negatively charged. It is one of the three types of particles that make up atoms. Along with protons, neutrons form the core, or nucleus, of an atom. Like protons, neutrons contain smaller particles called quarks. Each neutron is made of two “down” quarks and one “up” quark.
Atoms of the same element always have the same number of protons. But they can have different numbers of neutrons. Those variations of an element are called isotopes. All elements have isotopes. And at least one isotope of every element is unstable, or radioactive. That means they spontaneously give off a kind of energy called radiation. Releasing this energy allows the unstable atoms to transform, or decay, into more stable states. Sometimes, this decay involves neutrons transforming into other particles.
Neutrons are useful tools for probing the structure and behavior of matter. When researchers fire a beam of neutrons at a material, those neutrons bounce off atoms in the material. The way the neutrons scatter reveals the material’s properties.
Other types of experiments scatter light particles (such as X-rays) or electrons off materials. But light particles and electrons bounce off the electron clouds that surround atoms. They don’t reach the atom’s nucleus. Neutrons do. Neutrons cut through those clouds and bounce off an atom’s nucleus. This allows scientists to probe materials more deeply. Neutrons also do not harm materials the way other test particles do. This allows neutron scattering to be used on delicate materials. Examples include tissue samples and archaeological artifacts.
In a sentence
Corpses of exploded stars called neutron stars are made almost entirely of neutrons.
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