AQA GCSE FOUNDATION PHYSICS - Understanding Half-Life and Radioactivity

Understanding Half-Life and Radioactivity

What is Radioactivity?

Radioactivity is the process where an unstable atom decays into a more stable atom by releasing energy in the form of radiation. This radiation comes in different forms:

• Alpha (?) radiation: Consists of two protons and two neutrons, effectively a Helium nucleus. It has a high ionising power (meaning it can easily knock electrons off atoms) but a short range.
• Beta (?) radiation: Consists of high-speed electrons or positrons. It has a moderate ionising power and range.
• Gamma (?) radiation: Consists of electromagnetic radiation. It has low ionising power but a long range.

What is Half-Life?

The half-life of a radioactive isotope is the time it takes for the number of radioactive atoms in a sample to halve. It's a crucial concept in understanding radioactivity because it helps us measure how quickly a radioactive substance decays.

Imagine this: You have a radioactive sample with 100 unstable atoms. After one half-life, 50 atoms will have decayed, leaving 50 undecayed atoms. After another half-life, 25 atoms will decay, leaving 25 undecayed. This process continues until all the atoms in the sample are stable.

Key points about half-life:

• Constant: The half-life of a particular radioactive isotope is always the same, regardless of the amount of the isotope present.
• Independent of external factors: Half-life is not affected by temperature, pressure, or any other external factors.
• Useful for dating: Half-life is used to determine the age of ancient objects or fossils through radioactive dating.

Applications of Half-Life:

1. Radioactive Dating:

• Carbon-14 Dating: This technique is used to date fossils and artifacts up to around 50,000 years old. It relies on the decay of carbon-14, a radioactive isotope of carbon, with a half-life of 5,730 years.

2. Medical Applications:

• Radiotherapy: Radioactive isotopes are used in radiation therapy to kill cancer cells.
• Medical Imaging: Radioactive isotopes can be used to create images of the inside of the body, helping diagnose medical conditions.

3. Industrial Applications:

• Gauging: Radioactive isotopes can be used to measure the thickness of materials, such as paper or metal sheets.
• Tracing: Radioactive isotopes can be used to track the movement of substances, such as water flow in pipes or the movement of pollutants in the environment.

Key Formula:

Number of undecayed atoms = Initial number of atoms × (1/2)^(time elapsed / half-life)

This formula allows you to calculate the number of undecayed atoms at any given time, given the initial number of atoms, the half-life of the isotope, and the time elapsed since the start of the decay process.

Conclusion:

Understanding half-life is crucial in grasping the concepts of radioactive decay and its diverse applications. From dating ancient artifacts to diagnosing medical conditions, half-life plays a significant role in various fields.