Neutron
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.
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.
Isotopes
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.
Neutron Media
- Quark structure neutron.svg
Neutron quark structure (ring-shape)
- Blausen 0342 ElectronEnergyLevels.png
Models depicting the nucleus and electron energy levels in hydrogen, helium, lithium, and neon atoms. In reality, the diameter of the nucleus is about 100,000 times smaller than the diameter of the atom.
Nuclear fission caused by absorption of a neutron by uranium-235. The heavy nuclide fragments into lighter components and additional neutrons.
- Beta Negative Decay.svg
The principal Feynman diagram for decay of a neutron into a proton, electron, and electron antineutrino via an intermediate heavy boson
- Electron Capture Decay.svg
The principal Feynman diagram for decay of a proton into a neutron, positron, and electron neutrino via an intermediate heavy boson
A schematic of the nucleus of an atom indicating radiation, the emission of a fast electron from the nucleus. The decay also creates an antineutrino (omitted) and *converts a neutron to a proton within the nucleus. *The inset shows beta decay of a free neutron; an electron and antineutrino are created in this process.
- Institut Laue–Langevin (ILL) in Grenoble, France.jpg
Institut Laue–Langevin (ILL) in Grenoble, France – a major neutron research facility
Related pages
References
- ↑ 1.0 1.1 Woolley, Steve (2011). Edexcel IGCSE Physics Revision Guide. Pearson Education. p. 20-21. ISBN 9780435046736.
- ↑ 2.0 2.1 Cox, Brian; Cohen, Andrew (2011). Wonders of the Universe. HarperCollins. p. 79, 108. ISBN 9780007395828.
- ↑ Ryan, Lawrie (2001). Chemistry for you: revised National Curriculum edition for GCSE (Second ed.). Nelson Thornes. p. 29. ISBN 9780748762347.
- ↑ "Ernest Rutherford". chemed.chem.purdue.edu.
- ↑ 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.
- ↑ "The Nobel Prize in Physics 1935: James Chadwick". Nobelprize.org. Retrieved 2011-04-15.
- ↑ 8.0 8.1 8.2 "Neutron (subatomic particle)". Encyclopædia Britannica Online. Encyclopædia Britannica. Retrieved 2011-04-14.
