nucleon (constituent of the nucleus of the atom) that has neutral electric charge (no charge); symbol n
(Redirected from Neutrons)

Neutrons, with protons and electrons, make up an atom. Neutrons and protons are found in the nucleus of an atom.[1][2][3] Unlike protons, which have a positive charge, or electrons, which have a negative charge, neutrons have zero charge[1][4] which means they are neutral particles. Neutrons bind with protons with the residual strong force.

A picture of a neutron. The 'u' stands for an up quark, and the 'd' stands for a down quark.

Neutrons were predicted by Ernest Rutherford,[5] and discovered by James Chadwick,[6][7] in 1932.[6] Atoms were fired at a thin pane of beryllium. Particles emerged which had no charge, and he called these 'neutrons'. They were later added to the modern image of the atom.

Neutrons have a mass of 1.675 × 10-24g,[8] which is a little heavier than the proton.[8] Neutrons are 1839 times heavier than electrons.[8]

Like all hadrons, neutrons are made of quarks. A neutron is made of two down quarks and one up quark.[2][3] One up quark has a charge of +2/3, and the two down quarks each have a charge of -1/3. The fact that these charges cancel out is why neutrons have a neutral (0) charge. Quarks are held together by gluons.



Neutrons can be found in almost all atoms together with protons and electrons. Hydrogen-1 is the only exception. Atoms with the same number of protons but a different number of neutrons are called isotopes of the same element.

The number of neutrons in an atom does not affect its chemical properties. However it affects its half-life, a measure of its stability. An unstable isotope has a short half-life, in which half of it decays to lighter elements. By contrast, a stable isotope has a long half-life, much longer than that of an unstable isotope. The stability of an isotope is related to radioactivity: an unstable isotope can be highly radioactive.

Atomic reactions


Neutrons are the key to nuclear chain reactions, nuclear power and nuclear weapons.



  1. 1.0 1.1 Woolley, Steve (2011). Edexcel IGCSE Physics Revision Guide. Pearson Education. p. 20-21. ISBN 9780435046736.
  2. 2.0 2.1 Cox, Brian; Cohen, Andrew (2011). Wonders of the Universe. HarperCollins. p. 79, 108. ISBN 9780007395828.
  3. 3.0 3.1 Nave, R. (2007-01-15). "Protons and neutrons". Retrieved 2011-07-15.
  4. Ryan, Lawrie (2001). Chemistry for you: revised National Curriculum edition for GCSE (Second ed.). Nelson Thornes. p. 29. ISBN 9780748762347.
  5. "Ernest Rutherford".
  6. 6.0 6.1 "Discovery of Neutrons". Helmholtz Zentrum Berlin. 2008-08-23. Archived from the original on 2010-11-13. Retrieved 2011-04-14.
  7. "The Nobel Prize in Physics 1935: James Chadwick". Retrieved 2011-04-15.
  8. 8.0 8.1 8.2 "Neutron (subatomic particle)". Encyclopædia Britannica Online. Encyclopædia Britannica. Retrieved 2011-04-14.