Not each atomic nucleus may exist infinitely long time. Some nuclei are capable spontaneously transform to another with emanation of invisible penetrating radiation. They are called unstable and indicated phenomenon is called radioactivity. There are three types of radiation with different physical nature: alpha rays, beta rays and gamma rays. Alpha rays are the stream of particles, constituting the system of two protons and two neutrons, connected together (the ions of helium). Beta rays are generated in nuclear processes of conversion of proton into neutron and vice versa. It distinguishes beta-plus and beta-minus decays. The first involves the transformation of a proton into neutron, a positron and neutrino. The second involves the transformation of a neutron into a proton, an electron and antineutrino. Usually all types of radioactivity are accompanied of emanation gamma rays, constituting the streams of photons with wavelength order of 10-9 ? 10-11 ñm. The important characteristic of radioactivity of atoms is half-life ? the amount of time it takes for half of a given number of nuclei to decay. This simulation shows phenomenon of radioactivity for several unstable isotopes. You can select nucleus and change the time interval over which you will observe radioactive decay for 100 atoms. One atom is demonstrated in left below window as a megascopic. Based on observations determine the half-life and identify the decay process for selected radioactive isotope. With help of check boxes ?Reaction? and ?Half-life? you can to control your answer.