All matter is composed of particles like atoms and molecules. We know that electrons orbit neutrons and protons in nucleus. What else is there about the nucleus? Well, in 19th century, the discovery of radioactivity made it possible to record interesting observations:
- It was found that the nuclei of radioactive elements were unstable and emit electro‐magnetic radiation spontaneously.
- Use of radioactive isotopic traces to study reaction mechanisms, material flow, and the composition of elements.
- Use of ionizing radiation to kill bacteria and destroy cancerous cells.
- Use of radioactivity to estimate a material’s age by measuring the radioactive decay.