For 10 points, name this subatomic particle with no net electric charge, slightly heavier than a proton.
Francisco-Miguel Marqués has hypothesized a stable cluster of four of these particles, which consist of two down quarks and one up quark. When these particles are in free space they rapidly undergo beta decay and have an average lifespan of about fifteen minutes. Discovered in 1932 by James (*) Chadwick, the number of these particles determines the isotope of an element, and their number is included in atomic mass but not atomic number. For 10 points, name this subatomic particle with no net electric charge, slightly heavier than a proton.
Francisco-Miguel Marqués has hypothesized a stable cluster of four of these particles, which consist of two down quarks and one up quark.
{neutron}