Radioactivity Study Guide

Radioactive decay is a random process at the level of individual nuclei. This means it is impossible to predict exactly when a specific unstable nucleus will decay. There is no external factor that can influence its decay, and it does not 'age' or wear out. However, when dealing with a very large quantity of identical unstable nuclei, the overall decay behaviour becomes predictable. The concept of half-life is used to quantify this predictability. Half-life is the average time it takes for half of the radioactive nuclei in a sample to decay. While individual decay is random, the statistical behaviour of a large population allows us to accurately estimate the reduction in activity over specific time periods related to the half-life.

The half-life of a radioactive isotope is the time taken for half of the radioactive nuclei in a sample to decay. This property remains constant for each isotope, regardless of the starting amount. To calculate how much of a substance remains after a certain time, first divide the total time by the half-life to determine the number of half-lives. Then, use: Remaining amount = Initial amount × (1/2)^(number of half-lives). When plotted on a graph, this process produces a smooth, downward curve known as an exponential decay—each equal time interval sees the amount halve, rather than decrease at a steady rate.