Neutron
The neutron is a subatomic particle, symbol n or n0, that has no electric charge and a mass slightly greater than that of a proton.
- discovered_by
- James Chadwick
- mass
- slightly greater than that of a proton
- charge
- none
- composition
- three quarks
- mean_lifetime_free
- about 15 minutes
- decay_products
- proton, electron, antineutrino
Lore & Background
Throughout the 1920s, physicists assumed the atomic nucleus was composed of protons and nuclear electrons, but this model was inconsistent with quantum theory.
Reader's Guide
The neutron is a fundamental component of atomic nuclei, found together with protons in all nuclei except the most common isotope of hydrogen. Neutrons determine the isotope of an element, and free neutrons are produced copiously in nuclear fission and fusion. They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission, fusion, and neutron capture processes. Neutron stars, formed from massive collapsing stars, consist of neutrons at the density of atomic nuclei but a total mass more than the Sun. Neutrons are not elementary particles; each is composed of three quarks. A free neutron spontaneously decays to a proton, an electron, and an antineutrino with a mean lifetime of about 15 minutes. Dedicated neutron sources produce free neutrons for irradiation and scattering experiments. Free neutrons do not directly ionize atoms but indirectly cause ionizing radiation, posing a biological hazard depending on dose. A small natural neutron background exists on Earth from cosmic rays and spontaneous fission of elements in the Earth's crust.
Did You Know?
- A free neutron decays to a proton, an electron, and an antineutrino with a mean lifetime of about 15 minutes.
- Neutrons are composed of three quarks and are not elementary particles.
- The name 'neutron' derives from the Latin root for neutralis and the Greek suffix -on.
Frequently Asked Questions
What is a neutron?
A neutron is a neutral subatomic particle (symbol n or n⁰) carrying no electric charge and weighing just slightly more than a proton. It sits alongside protons inside atomic nuclei as one of the two main building blocks of matter.
What is a neutron made of?
A neutron is built from three quarks held together by the strong nuclear force. Although those quarks carry individual electric charges, their combination results in a net charge of zero for the whole particle.
How long does a free neutron last?
Once outside a nucleus, a neutron is unstable and decays with a mean lifetime of about 15 minutes. It breaks apart into a proton, an electron, and an antineutrino in a process called beta decay.
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