Explanation : Mesons are not produced by radioactive decay but appear in nature only as short-lived products of very high-energy interactions in matter, between particles made of quarks. Mesons are hadronic subatomic particles found in cosmic rays. They are composed of one quark and one anti-quark. bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometer, i.e. about 2/3 the size of a proton or neutron. All mesons are unstable. with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay to form electrons and neutrinos. ....Read more