Abstract
The present chapter is an introduction to various scientific and technological
fields. It is a beginning step to trail further study in this book. The first chapter
specifies the contemporary idea and fundamental understandings of nuclear physics,
which is necessary to develop the rest of the studies in this domain. The present chapter
deals with an introduction to nuclei, constituents of the nucleus and its properties, mass
defects and binding energy, nuclear reactions, the Q-value of nuclear reactions, and the
discovery of the neutron and nuclear chain reactions.