Nuclear particles are subatomic particles that make up the nucleus of an ATOM. A meson is a type of nuclear particle with 5 letters and is composed of one quark and one antiquark. A proton is a type of nuclear particle with 6 letters and is composed of two up quarks and one down quark. An ATOM is a type of nuclear particle with 4 letters and is composed of protons, neutrons, and electrons. A positron is a type of nuclear particle with 8 letters and is the antiparticle of the electron. Finally, a pion is a type of nuclear particle with 4 letters and is composed of either two up quarks or two down quarks.