Understanding Decay Chains in Nuclear Physics | U238 Example Explained

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In summary, the conversation is about predicting which nuclides will undergo alpha decay. The speaker has been reading about atomic and nuclear physics, but is still confused. They mention a rule that states most nuclides undergoing alpha decay are found in the top right corner of the chart of nuclides, but are looking for a more definite explanation. The other person suggests using a mass formula to determine if a nuclide is available for alpha decay.
  • #1
hamurph
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Good afternoon, all.

Firstly, I apologise if this question is a bit daft, I have just started a nuclear physics course so I am only a baby :smile: (I have also been reading ahead so that may be causing most of my problem!)

Looking at the U238 deay chain as an example, I understand that anything with a Protron No. above the line of stability on the Nuclide chart go through Beta+ or electron capture and anything below the line of stability go through Beta- decay.

What is confusing me is how do I predict which ones will go through Alpha decay? Alpha decay occurs from U238 right down to when it stabilises at Pb206!

I have been reading an e-book on atomic and nuclear physics and all it says is "Most Nuclides that will undergo Alpha decay are found in the top Right hand corner of the chart of nuclides" - I was hoping for something like "Where the No. of Neutrons of the isotope exceed the stable isotope's neutrons by X" or something more definite\layman :rolleyes:

Thank you anyone who helps me and feel free to laugh and jeer!

Hamurph

p.s. I am sure you guys are more than familiar, but I have attached a picci of the U238 series because I think it looks nice :smile:
 

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  • #2
Yoo look the masses. If Mass of Candidate - Mass of procuct > Mass of He4, you can suspect the particle is available for alpha decay.


Then in a next step you look for a mass formulae, one of these giving you the mass as a function of (A,Z), and apply it above so you derive again the intuitive rule ("upper side of the table") but with some quantitative meat.
 
  • #3


Hi Hamurph,

No need to apologize, we all have to start somewhere and asking questions is a great way to learn! Decay chains in nuclear physics can be a bit confusing at first, but with some practice and understanding, it will become clearer.

To predict which nuclides will go through alpha decay, we need to look at the stability of the nucleus. As you mentioned, nuclides above the line of stability tend to undergo beta+ or electron capture, while those below undergo beta- decay. However, nuclides that are too large (with too many protons and neutrons) tend to be unstable and undergo alpha decay to reach a more stable state.

In the case of U238, it has 92 protons and 146 neutrons, which is a large number of particles for a nucleus. As it undergoes radioactive decay, it transforms into smaller, more stable nuclides. This process continues until it reaches a stable state at Pb206. The reason why alpha decay occurs throughout this decay chain is because U238 is too large and unstable, and needs to shed particles to reach a more stable state.

So, to answer your question, there is no specific number or rule for predicting which nuclides will undergo alpha decay. It depends on the stability of the nucleus and its size. The top right hand corner of the chart of nuclides tends to have larger, unstable nuclides, which is why you often see alpha decay occurring in that region.

I hope this helps to clarify things for you. Keep asking questions and keep learning! And thank you for sharing the U238 series, it does look nice :smile:
 

1. What is a decay chain in nuclear physics?

A decay chain in nuclear physics refers to the series of radioactive decays that a parent nucleus undergoes in order to become a stable daughter nucleus. This process involves the emission of particles and energy until the parent nucleus reaches a stable state.

2. How does uranium-238 (U238) illustrate a decay chain?

Uranium-238 is a naturally occurring radioactive isotope that has a long half-life of 4.5 billion years. It undergoes a series of decays, starting with alpha decay, to reach a stable state of lead-206. This decay chain includes multiple intermediate daughter nuclei, each with their own specific half-life and decay mode.

3. What is the significance of understanding decay chains in nuclear physics?

Understanding decay chains is crucial for many applications of nuclear physics, including nuclear energy, nuclear medicine, and radiocarbon dating. It allows us to predict the behavior and stability of radioactive nuclei, as well as the types and amounts of radiation emitted during the decay process.

4. How is the rate of decay determined in a decay chain?

The rate of decay in a decay chain is determined by the half-life of each individual decay step. The half-life is the amount of time it takes for half of the parent nuclei to decay into daughter nuclei. The overall rate of decay in a chain is equal to the product of the individual half-lives.

5. Can decay chains be manipulated or controlled?

No, decay chains cannot be manipulated or controlled. The rate of decay and the specific decay modes of each nucleus in a chain are determined by the fundamental properties of each individual nucleus. However, scientists can use various techniques to slow down or speed up the rate of decay, such as through the use of nuclear reactors or accelerators.

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