The Neutron

<p><strong>The Field Guide to Particle Physics <br></strong><a href="https://pasayten.org/the-field-guide-to-particle-physics">https://pasayten.org/the-field-guide-to-particle-physics</a><br>©2021 The Pasayten Institute <a href="https://creativecommons.org/licenses/by-sa/4.0/">cc by-sa-4.0</a><br>The definitive resource for all data in particle physics is the Particle Data Group: <a href="https://pdg.lbl.gov/">https://pdg.lbl.gov</a>.</p><p>The Pasayten Institute is on a mission to build and share physics knowledge, without barriers! <a href="http://pasayten.org/heysean">Get in touch</a>.</p><p><strong>The Neutron<br></strong><br>With a mass of 939.565 MeV, the neutron is the second lightest baryon - that is, a particle made up of three quarks. The neutron's quarks include <a href="https://pasayten.org/the-field-guide-to-particle-physics/up-and-down-quarks">one up and two downs</a>, so it is total electric charge is zero:</p><p><br>2/3e − 2×1/3e = 0</p><p>The neutron may be electrically neutral, but don’t let that fool you, it still interacts with the <a href="https://pasayten.org/the-field-guide-to-particle-physics/photon">electromagnetic field</a>.</p><p><br>Like the earth - and the <a href="https://pasayten.org/the-field-guide-to-particle-physics/proton">proton</a> - the neutron has a tiny magnetic field. It's a dipole field: with a north and south pole. Because moving electric charges generate magnetic fields, you might expect a spinning electric charge, like the proton, to have a magnetic field, but not the neutron. And yet it does.</p><p>What’s curious about the neutron’s magnetic field is that its so strong. It’s about 60% that of proton, although oppositely orientated. This fact was probably the first clue that the neutron wasn’t a fundamental particle, but was made up of some other junk.</p><p>The neutron is just a tiny bit heavier than the proton, which is fitting given that the down quark is just a tiny bit heavier than the up quark. Because the up and down quarks are related by the weak nucle