Chapter 3 - Radioactivity

Abstract

This chapter discusses the concepts related to nature of radionuclides and radioactivity processes. Radionuclides are unstable nuclides that achieve greater stability by undergoing nuclear transformations. The nuclide may emit alpha or beta particles when the ratio of neutrons to protons in the nucleus is unfavorable for the state of stability. If, after the emission of the particle, the nuclide is still in an energetically unstable state, then it may emit a gamma ray for transition from the excited nuclear level to the stable ground level with no further change in the neutron to proton ratio. The intensity of a radioactive source (activity) is determined by the rate of nuclear transformations per unit of time. According to the law of radioactive decay, the probability with which a radionuclide decays is a characteristic and immutable constant associated with a particular radionuclide, and this probability cannot be influenced by ambient conditions or their variation. The average lifetime of a radionuclide atom is an important and definable quantity, which is predictable on a statistical basis. Chain decay is the process of nuclear transformation in which a radionuclide decays consecutively through a series of radionuclides to a stable nuclide. Another possible pathway of complex radioactivity decay is branching decay when the parent radionuclide is capable of undergoing either of two possible transformations. The chapter describes the properties of different types of radioactive decay, such as decay by alpha-particle emission, negative electron emission decay, positive electron decay, and decay by electron capture.