This book has been divided into four chapters theory of atomic structure, nuclear detectors, acceleration, nuclear forces in order to limit the volume of the book. A working knowledge of theory of relatively some basic ideas of atomic and molecular physics has been explained on the part of the reader. The book is very useful for the students of graduate and post graduate level and the candidate appearing for the various competitive examination like PCS and IAS. Suggestions for the improvement of the book shall be grateful acknowledge and incorporated in the next addition. Contents: Theory of Atomic Structure, Nuclear Detectors, Acceleration, Nuclear Forces.