This book has been divided into four chapters Radioactivity and Isotopes, alpha-particles beta-decay, gamma Radiations. This book is very helpful for the students of Degree/Honours and post graduates. This book is also very useful to the candidate appearing in the various competitions like I.A.S and others. Contents, Preface I. RADIOACTIVITY AND ISOTOPES : 1. Introduction 2. Fundamental Laws of Radioactivity 3. Radioactive Equilibrium 4. Units of Radioactivity 5. Radioactive Branching 6. Roentgen 7. Induced Radioactivity 8. Measurement of Decax Constants 9. Radioactive Dating : The Age of the Earth 10. Natural Radioactive Series 11. Isotopes II. ALPHA PARTICLES : 1. Introduction 2. Determination of Q/M for the a-Particle 3. Range of cc-Particles 4. Range Velocity-Energy Life Relations 5. Alpha Energy Mass Number 6. Alpha Particle Spectra 7. Gamow`s Theory of Alpha Decay III. BETA-DECAY : 1. Introduction 2. Beta-Spectroscopy 3. The Neutrino Hypothesis 4. Energy Half-Life Relationships 5. Fermi Theory of Beta Decay 6. Electron Capture 7. Violation of Parity Conservation in P-decay 8. Helicity IV. GAMMA Radiation : 1. Introduction 2. Measurement of Gamma Ray Energies 3. Multipole Radiations 4. Internal Conversion 5. Internal Pair Creation 6. Nuclear Isomerism 7. Angular Correlation in Gamma Emission 8. Coulomb Excitation 9. Resonance Fluorescence 10. Mossbauer Effect