Radioactive decay - waves and particles Study Guide

Radioactive decay is a fundamental process where unstable atomic nuclei spontaneously transform into more stable forms by emitting particles and/or energy. This process is inherently random, meaning we cannot predict precisely when a single individual unstable nucleus will decay. It's like flipping a coin for each atom – you can't know when any specific coin will land on 'decay'. However, for a very large number of identical unstable nuclei, we can predict the rate of decay statistically. This statistical measure is called the half-life. The half-life is defined as the time taken for half of the radioactive nuclei in a sample to decay. Alternatively, it can be defined as the time taken for the activity of a sample to fall to half of its initial value. Because radioactive decay is random, each half-life period will see exactly half of the *remaining* radioactive nuclei decay. So, if you start with 1000 radioactive nuclei, after one half-life, you'll have 500 left. After a second half-life, you'll have 250 left, and so on. The total number of nuclei does not disappear; they transform into stable products. The half-life is a constant value for a specific isotope and is not affected by external factors like temperature, pressure, or chemical state. This consistency makes half-life a crucial concept for dating ancient artefacts, medical diagnostic imaging, and understanding nuclear power.

Some atomic nuclei are unstable, meaning they possess an excess of energy or an imbalance of protons and neutrons, making them prone to change. To achieve a more stable state, these unstable nuclei may undergo radioactive decay, where they spontaneously emit radiation and often transform into different elements. This emitted radiation, which can be alpha particles, beta particles, or gamma rays, carries energy away from the nucleus. When these particles interact with other atoms or particles, they transfer some of this energy, potentially causing ionisation or other changes. In certain heavy, unstable nuclei, such as Uranium-235, the nucleus can split into smaller nuclei in a process called nuclear fission. This fission event releases a significant amount of energy, along with additional neutrons. If these released neutrons strike other unstable nuclei, they can induce further fission events, leading to a self-sustaining process known as a nuclear chain reaction. This chain reaction can be controlled, as in nuclear power reactors to generate electricity, or uncontrolled, as in nuclear weapons, where a rapid and massive energy release occurs. The understanding of these processes is fundamental to applications ranging from medical imaging and cancer treatment to nuclear power generation and weapons technology.