The book "Worlds within worlds: The history of nuclear power, Volume 2 (of 3) Mass and energy; Neutron; The structure of the nucleus" by Isaac Asimov is a fascinating scientific encyclopedia that reveals to the reader the mysterious world of atomic physics and nuclear power. In this book, the fundamental concepts of mass, energy, neutron, and the structure of the nucleus are studied, their properties and relationships are revealed. The author successfully combines an accessible writing style with deep scientific knowledge, which makes this book interesting both for professionals in the field and for the general public interested in the secrets of nuclear physics.