By measuring the mass of different atoms, it is possible to guess that the nucleus is made of two particles, the proton and the neutron. Different kinds of atoms have different numbers of protons and of neutrons. This leaves one question. We will answer this later. Soon other particles were discovered.
Cosmic rays are particles that enter the earth's atmosphere from space.
Dr. Bloom demonstrated a device called a scintillation detector, whenever a particle passes through this device, a flash of light appears. The particles with the highest energies detected so far have been from cosmic rays. In the late 1920s, quantum mechanics predicted that there must be a particle that has the opposite charge to the electron, which we now call a positron. The positron was discovered in 1931. Almost all particles have an antiparticle with equal mass and opposite charge.