ABSTRACT
A number of radioactive nuclei are naturally occurring, that is nuclei which since their genesis with the formation of the Earth continue to exist in spite of their decay, or those nuclei which are continuously being created through bombardment by cosmic rays. Radioactive nuclei can also be obtained artificially by the bombarding of stable nuclei with energetic particles. It should be noted that there is no physical difference between natural and artificial radioactivity even though the circumstances of their origin are different. Radioactive decay is characterized by the time of duration, type or types of particles emitted, their energy and, in the case of some of the particles which are emitted, by their angular correlation, that is the relative angle between the directions of emission of the emerging particles. The number of elements is limited because nuclei become increasingly unstable with respect to spontaneous fission and α-decay as the proton number increases.
