Radioactive decay - waves and particles Study Guide

The hazards associated with radioactive materials are directly influenced by their half-life. Half-life is the time it takes for half of the radioactive nuclei in a sample to decay. This means that after one half-life, the activity of a radioactive sample is halved. After two half-lives, it's halved again to a quarter of its original activity, and so on. The activity of a radioactive source determines the rate at which radiation is emitted, and therefore, the intensity of the hazard it poses.

Materials with a short half-life decay quickly, meaning they emit radiation very intensely for a short period. This makes them extremely dangerous if mishandled, as a large amount of radiation is released in a short time. However, their activity drops rapidly, so they become relatively safe much sooner. For example, radioisotopes used in medical imaging often have short half-lives so that they decay quickly within the patient's body, minimising long-term exposure.

Conversely, materials with a long half-life decay slowly. This means their activity decreases very gradually over extended periods, sometimes thousands or millions of years. While the intensity of radiation at any given moment might be lower than a short-lived source, the cumulative exposure over time can be significant. These materials remain hazardous for extremely long durations, posing long-term disposal and storage challenges. For instance, nuclear waste contains isotopes with very long half-lives, requiring secure geological disposal to prevent environmental contamination and protect future generations from prolonged exposure.

Atoms consist of a central nucleus, made up of protons and neutrons, surrounded by electrons arranged in energy levels or shells. Changes within these components can lead to the emission or absorption of electromagnetic radiation across a wide range of frequencies, from low-frequency radio waves to high-frequency gamma rays. When electrons in an atom move between different energy levels, they can either emit or absorb photons of electromagnetic radiation. If an electron moves from a higher energy level to a lower one, it emits a photon with energy equal to the difference between the two energy levels. Conversely, if an electron absorbs a photon with the correct amount of energy, it can jump from a lower energy level to a higher one. This process explains why elements have characteristic emission and absorption spectra.

Changes within the nucleus of an atom also result in the emission of radiation. Unstable nuclei undergo radioactive decay, transforming into more stable nuclei while emitting particles (like alpha and beta particles) and/or electromagnetic radiation (gamma radiation). Alpha particles are helium nuclei, beta particles are high-energy electrons or positrons, and gamma rays are high-frequency electromagnetic waves. These nuclear changes involve significant energy transformations, often much greater than those involved in electron transitions, leading to the emission of radiation with very high frequencies. For instance, gamma rays are the highest frequency form of electromagnetic radiation and are produced during nuclear decay.

Electromagnetic radiation is a form of energy that travels in waves and includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. The frequency of the emitted or absorbed radiation depends directly on the energy difference involved in the atomic or nuclear transition. Higher energy transitions correspond to higher frequency radiation. Understanding these processes is fundamental to fields such as spectroscopy, medical imaging, and nuclear energy.