Nuclear Half Life: Intro and Explanation

Tyler DeWitt

20 May 201205:53

Summary

TLDRThis video explains the concept of nuclear half-life, focusing on how it determines the time it takes for half of a radioactive element to decay into another element. Using thorium-234 as an example, the video illustrates how it decays into protactinium through beta decay, with its half-life being 24 days. The video also highlights different half-lives for various elements, such as uranium-238 with a half-life of 4.5 billion years and polonium-218 with a half-life of just three minutes, demonstrating the wide range of nuclear decay times.

Takeaways

⚛️ Nuclear half-life is the time it takes for half of a radioactive substance to decay.
🔄 In a nuclear process, the number of protons and neutrons in an atom's nucleus changes.
💡 An example is thorium-234 undergoing beta decay, where a neutron turns into a proton, transforming thorium into protactinium.
📉 The half-life of thorium-234 is 24 days, meaning every 24 days, half of the thorium decays into protactinium.
🧪 After 24 days, 80 grams of thorium becomes 40 grams, then 20 grams after another 24 days, and so on.
⏳ The half-life process continues, reducing the amount of thorium by half with each cycle, but it doesn't disappear—it changes into another element.
📊 Half-life is represented as T1/2, and different elements have different half-lives based on their decay process.
🌍 Uranium-238, for example, has a half-life of 4.5 billion years, taking that long for half of it to decay.
⏱️ Polonium-218, on the other hand, has a very short half-life of only three minutes, decaying rapidly into lead.
🧮 The key concept is that half-life is the time needed for half of a sample to decay into something else.

Q & A

What is nuclear half-life?
-Nuclear half-life is the time it takes for half of a radioactive substance to undergo a nuclear process, where the number of protons and neutrons in the nucleus changes.
What happens during beta decay?
-During beta decay, a neutron in the atom's nucleus turns into a proton, increasing the number of protons in the nucleus and changing the element.
What is the significance of the number of protons in an atom?
-The number of protons in an atom determines what element the atom is. A change in the number of protons results in the atom becoming a different element.
In the example given, what element does thorium-234 decay into?
-Thorium-234 decays into protactinium-234 after undergoing beta decay, where one neutron turns into a proton.
What is the half-life of thorium-234?
-The half-life of thorium-234 is 24 days, meaning it takes 24 days for half of the thorium sample to decay into protactinium-234.
How does the amount of thorium change after each half-life?
-After each half-life, the amount of thorium decreases by half. For example, after the first 24 days, 80 grams becomes 40 grams, then 20 grams after another 24 days, and so on.
How can nuclear half-life be represented in equations?
-Nuclear half-life is often represented with the notation T½, indicating the time it takes for half of a sample to decay.
Do all radioactive elements have the same half-life?
-No, different radioactive elements have different half-lives. For example, uranium-238 has a half-life of 4.5 billion years, while polonium-218 has a half-life of just 3 minutes.
What happens to uranium-238 during its decay process?
-Uranium-238 undergoes alpha decay, turning into thorium-234. This process has a half-life of 4.5 billion years.
Why is it important to understand nuclear half-life?
-Understanding nuclear half-life is important because it helps scientists predict how long it takes for radioactive materials to decay, which has applications in fields like nuclear energy, medicine, and environmental studies.

Outlines

00:00

🔬 Understanding Nuclear Half-Life

This paragraph introduces the concept of nuclear half-life, explaining that it describes the time it takes for nuclear processes, where the number of protons and neutrons in an atom's nucleus changes, to occur. The example given is the beta decay of thorium-234, where a neutron turns into a proton, transforming the element into protactinium. The explanation continues with a practical example, showing how thorium decays over time, reducing by half every 24 days until most of the sample has changed into protactinium. The key takeaway is that half-life refers to the time required for half of a material to undergo decay, and it's often denoted as T 1/2.

05:00

⏳ Half-Life Variation Across Elements

This paragraph expands on the concept of half-life by discussing how different nuclear processes have vastly different half-lives. For example, uranium-238 has a half-life of 4.5 billion years, while polonium-218 has a much shorter half-life of only three minutes. The example illustrates how, in a laboratory setting, half of a polonium-218 sample could decay in the time it takes for a brief break. The paragraph emphasizes that the half-life varies significantly depending on the element and decay process, providing contrasting examples to show the diversity in time scales for nuclear reactions.

Mindmap

Keywords

💡Nuclear half-life

Nuclear half-life is the time required for half of the atoms in a radioactive sample to decay. It is a measure of how long it takes for nuclear processes, such as the transformation of one element into another, to occur. In the video, the half-life of thorium is shown to be 24 days, meaning that every 24 days, half of the thorium decays into proactinium.

💡Nuclear process

A nuclear process refers to any change that occurs within the nucleus of an atom, specifically changes in the number of protons and neutrons. This transformation can lead to the creation of a different element. In the video, the example given is thorium-234 undergoing beta decay, where a neutron turns into a proton, thus changing the element into proactinium.

💡Beta decay

Beta decay is a type of radioactive decay where a neutron in an atom's nucleus is transformed into a proton and an electron. This changes the identity of the element, as the number of protons increases. In the video, thorium undergoes beta decay, which increases its proton count from 90 to 91, turning it into proactinium.

💡Thorium-234

Thorium-234 is a radioactive isotope of thorium that undergoes beta decay to transform into proactinium-234. The video explains that thorium-234 has a half-life of 24 days, meaning that every 24 days, half of a given sample of thorium will have decayed into proactinium.

💡Proactinium-234

Proactinium-234 is the element formed after thorium-234 undergoes beta decay. In the video, thorium’s decay process results in the production of proactinium, which marks the change of one element to another, a key concept in understanding nuclear decay.

💡Decay process

A decay process is the natural transformation of an unstable atomic nucleus into a more stable one, releasing energy in the form of radiation. In the video, the example given is the decay of thorium into proactinium, where half of the thorium decays every 24 days, demonstrating the concept of half-life.

💡Uranium-238

Uranium-238 is a radioactive isotope that undergoes alpha decay to form thorium-234. Its half-life is extremely long, approximately 4.5 billion years, which contrasts with other elements like polonium-218, as discussed in the video. This highlights the wide range of half-lives that different nuclear processes can have.

💡Alpha decay

Alpha decay is a type of radioactive decay where an atomic nucleus emits an alpha particle (composed of 2 protons and 2 neutrons). This reduces the atomic number by 2, changing the element. In the video, uranium-238 undergoes alpha decay to produce thorium-234, a process with a half-life of 4.5 billion years.

💡Polonium-218

Polonium-218 is a radioactive isotope mentioned in the video that undergoes alpha decay to form lead-214. Its half-life is extremely short—only three minutes. This contrasts with uranium-238, demonstrating how different nuclear reactions can have vastly different half-lives.

💡Graph of decay

The graph of decay represents the amount of a radioactive substance over time as it decreases exponentially. In the video, the graph illustrates how the quantity of thorium decreases by half every 24 days, visually demonstrating the concept of half-life.

Highlights

Nuclear half-life tells us how long it takes for nuclear processes to occur.

A nuclear process involves a change in the number of protons and neutrons in an atom's nucleus.

An example of a nuclear process is thorium-234 undergoing beta decay, where one of its neutrons turns into a proton.

When thorium-234 undergoes beta decay, it changes into protactinium-234 due to the increase in protons.

The half-life of thorium-234 is 24 days, meaning it takes 24 days for half of a thorium sample to decay into protactinium.

After each half-life, the remaining thorium is reduced by half: from 80 grams to 40 grams, from 40 to 20 grams, and from 20 to 10 grams.

Half-life refers to the time it takes for half of a sample of a radioactive element to decay into another element.

A graph of thorium's decay over time shows exponential reduction in the amount of thorium, with each bar representing a half-life period.

Half-lives vary greatly between elements: uranium-238 has a half-life of 4.5 billion years, while polonium-218 has a half-life of just 3 minutes.

Polonium-218's short half-life means that half of its sample would decay in 3 minutes, making it challenging to study without immediate observation.

For uranium-238, it would take 4.5 billion years for half of a sample to decay into thorium-234.

The time between each stage in a decay process differs based on the half-life of the element involved.

Half-life is crucial for understanding the time required for radioactive decay and is represented by the symbol T₁/₂.

The concept of nuclear half-life applies to different radioactive elements, each with its own distinct half-life duration.

Half-life calculations help predict the amount of time required for a specific amount of a radioactive element to decay.