Half life | Radioactivity | Physics | FuseSchool

Summary

This video explains the concept of radioactive decay and half-life, illustrating how unstable atomic nuclei undergo random decay. By measuring the time it takes for half of the atoms in a sample to decay, we can determine its half-life. Examples include radioactive isotopes like iodine-131 and carbon-14, used for dating objects and understanding decay rates. It also touches on the practical uses of radioactive materials in medicine and the environment, explaining that while some isotopes decay quickly, others, like strontium-90, remain for decades.

Takeaways

• 🔬 Radioactive decay is a random event, and we cannot predict when any single nucleus will decay.
• ⏳ The concept of half-life refers to the time it takes for half of a sample's atoms to decay.
• 🕒 In a given example, half of the atoms decayed in 5 seconds, so the half-life was 5 seconds.
• 🎲 A simple analogy for half-life: if you roll a bucket of dice and remove all the sixes, the time it takes for half the dice to be removed represents a half-life.
• 📉 A decay curve shows how the number of remaining atoms or radioactive activity decreases over time.
• 📅 Iodine-131 has a half-life of 8 days, meaning its radioactivity halves every 8 days.
• 🌿 Carbon-14, present in living organisms, has a half-life of 5730 years, and is used for radiocarbon dating.
• ⏱️ After death, the carbon-14 content decays, allowing scientists to estimate how many half-lives have passed since an organism died.
• ⚛️ Radiocarbon dating becomes unreliable after about 10 half-lives (55,000 years), as too little carbon-14 remains.
• ☢️ Strontium-90, produced by atomic weapons, has a half-life of 29 years and remains in the environment for over 120 years.

Q & A

What is the significance of an unstable nucleus in an atom?

An unstable nucleus in an atom may undergo radioactive decay at any moment, but the exact timing is unpredictable since decay is a random event.

How can we predict decay if we don't know when a single nucleus will decay?

While we can't predict the decay of a single nucleus, we can measure the rate of decay in a large sample of atoms and use the concept of half-life to estimate how long it takes for half of the atoms to decay.

What is meant by 'half-life'?

Half-life refers to the time it takes for half of the atoms in a radioactive sample to undergo decay. It is a measure of the rate of decay.

How is half-life demonstrated using dice in the example provided?

In the example, 100 dice are rolled, and all the ones showing a six are removed after each roll. The time taken for about half of the dice to be removed is analogous to one half-life, where the number of remaining dice halves with each round.

How can half-life vary between different isotopes?

Half-lives can vary widely, from fractions of a second (nanoseconds) to billions of years, depending on the isotope. Each isotope has a specific half-life.

What is the half-life of iodine-131, and how is it measured?

The half-life of iodine-131 is 8 days, and it is measured by observing that the radioactivity or count rate of iodine-131 halves every 8 days.

How does carbon-14 dating help estimate the time since death of an organism?

Carbon-14 dating estimates how many half-lives have passed since death by measuring the ratio of carbon-14 to carbon-12. For example, if a sample contains 25% of its original carbon-14, it has undergone two half-lives, or 11,460 years.

What is the limitation of radiocarbon dating?

Radiocarbon dating becomes unreliable after about 10 half-lives (approximately 55,000 years) because the remaining carbon-14 is too small to measure accurately.

Why are radionuclides with short half-lives used in medicine?

Radionuclides with short half-lives are used in medicine because they decay quickly, allowing patients to safely go home shortly after receiving treatment.

How long will strontium-90 from atomic detonations remain in the environment, and why?

Strontium-90 has a half-life of 29 years and will take over 120 years to begin significantly vanishing from the environment. This isotope originates from atmospheric nuclear detonations in the 1950s and 1960s.