# Radioactivity and Particles: Half-Life

## Radioactivity and Particles: Half-Life

- ‘Half-life’ refers to the length of time it takes for half the atoms in a radioactive substance to decay.
- It is impossible to predict when a particular atom will decay, but given a large number of atoms, predicting the average time for half of them to decay is possible. That’s the half-life.
- Half-life is not affected by physical factors such as temperature, pressure or state of the substance. It is a characteristic property of the radioactive isotope.
- Different isotopes have different half-lives, ranging from fractions of seconds to billions of years.
- After one half-life, the amount of radioactive material left is halved. After two half-lives, a quarter remains. After three half-lives, an eighth remains, and so on.
- Over time, a radioactive substance continues to decay and become less radioactive, but it never completely loses all its radioactivity.
- Half-life is crucial for determining the age of artefacts and fossils. This is known as radioactive dating or radiometric dating.
- It’s also important in managing radioactive waste, as some wastes remain hazardous for thousands of years.
- Real world applications include medical treatments, where doctors must carefully control the doses of radioactive treatment given to a patient, and in nuclear power plants, where half-life data helps control the reactors and prevent nuclear accidents.
- Half-life graphs can be plotted to visualise the decay of a radioactive substance. The horizontal axis traditionally represents time, and the vertical axis represents the number of undecayed atoms or the radioactivity.
- Calculating half-life involves understanding the exponential decay equation N = N0 * e^(-λt), where N is the final amount of undecayed material, N0 is the initial amount, λ is the decay constant, and t is time.
- Remember, completing practise problems involving half-life calculations will be beneficial in understanding the concept and preparing for exams.