Half-life Applications and Safety

Half-lives vary enormously: uranium-238 has a half-life of 4.5 billion years, whilepolonium-214 has a half-life of just 160 microseconds. This huge range makes different isotopes useful for different applications.

The formula for calculating remaining nuclei is:

Radioactive isotopes have many medical uses:

• Iodine-131 (half-life: 8 days): Treats thyroid cancer. The thyroid absorbs iodine, so radioactive iodine targets thyroid cells.
• Technetium-99m (half-life: 6 hours): Used as a tracer in medical imaging. Its short half-life means quick decay and minimal patient exposure.
• Cobalt-60: Gamma rays sterilize medical equipment without heat.
• PET scanning: Uses positron emitters to create detailed body images.

Carbon-14 dating works for organic materials up to about 60,000 years old. Living organisms absorb C-14 from the atmosphere. When they die, the C-14 decays with a half-life of 5,730 years. By measuring remaining C-14, we calculate when the organism died.

For older materials like rocks, potassium-40 dating (half-life: 1.3 billion years) oruranium-238 dating (half-life: 4.5 billion years) is used.

Three key safety principles:

• Shielding: Alpha stopped by paper, beta by aluminium, gamma needs thick lead
• Distance: Intensity decreases with distance squared—doubling distance quarters the intensity
• Time: Minimize exposure time to reduce total dose received