Half-life and Radioactive Dating - SS2 Physics Lesson Note
Half-life refers to the time it takes for half of the radioactive atoms in a sample to undergo radioactive decay. It is a fundamental concept in radioactivity and is used in various fields, including radioactive dating.
Half-life:
Half-life is a property specific to each radioactive isotope. It is defined as the time it takes for half of the radioactive atoms in a sample to decay. During radioactive decay, unstable atomic nuclei undergo a spontaneous transformation, resulting in the emission of radiation and the formation of more stable nuclei. The decay process follows an exponential decay law, where the number of radioactive atoms decreases by half in each successive half-life. Half-life is constant for a particular isotope and does not depend on the initial quantity of radioactive material or external factors.
Radioactive Dating:
Radioactive dating is a method used to determine the age of rocks, minerals, fossils, and other geological or archaeological materials based on the decay of radioactive isotopes. The principle behind radioactive dating is that the amount of parent isotope decreases over time due to radioactive decay, while the amount of daughter isotope increases. By measuring the ratio of parent to daughter isotopes in a sample and knowing the half-life of the parent isotope, scientists can calculate the age of the sample. Different isotopes have different half-lives, and the choice of the appropriate isotope depends on the age range of the material being dated. Common isotopes used in radioactive dating include carbon-14 (for dating organic materials up to about 50,000 years old), potassium-40 (for dating rocks and minerals up to billions of years old), and uranium-238 (for dating very old rocks and the Earth's age).
Application of Half-life and Radioactive Dating:
- Radioactive dating has numerous applications in various scientific disciplines.
- In geology, radioactive dating is used to determine the ages of rocks and the timing of geological events, such as volcanic eruptions and the formation of sedimentary layers.
- In archaeology and anthropology, radioactive dating is used to determine the ages of artefacts, fossils, and human remains, providing valuable insights into human history and evolution.
- In environmental science, radioactive dating is used to study the movement of pollutants, track groundwater flow, and estimate the age of Earth's formations.
- In medicine, radioactive dating is used in radiocarbon dating, which helps diagnose certain diseases and study metabolic processes in the body.
- Radioactive dating is also used in forensic science to analyse the age of evidence at crime scenes.
In summary, the half-life is the time it takes for half of the radioactive atoms in a sample to decay. It is a key concept in radioactivity and is used in radioactive dating to determine the age of materials. The decay of radioactive isotopes follows an exponential decay law, and by measuring the ratio of parent to daughter isotopes, scientists can calculate the age of the sample. This technique has important applications in geology, archaeology, anthropology, environmental science, medicine, and forensic science.