Analysis of Fusion & Fission by Binding Energy

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Summary:

I wanted to write a student article specially for those who don't have a background in nuclear physics. I've been suggested to share my basic understanding & ask if they're correct.
I would be grateful if anyone could explain where my mistakes are:
(Please note that diagrams are designed just to give a simple imagination of the article & make it more understandable; they do NOT correspond precise information.)
#6.jpg
In fusion reactions, lighter nuclei are combined into heavier ones (atomic mass increases); so the direction is from left to right (shown on the diagram). Therefore, in the fusion of 'light elements' the total final binding energy is higher (the related arrow points upward); so ##B_2-B_1>0## and energy is released. But for the fusion of 'heavy elements', the reverse is true, so ##B_2-B_1<0## and energy is needed.
#7.jpg
In fission processes, heavier nuclei split to lighter ones (atomic mass decreases); so the direction is from right to left. Thus, in the fission of 'light elements' total final binding energy is lower (the arrow points downward); so ##B_2-B_1<0## and energy is utilized. But according to the arrow pointing up, the fission of 'heavy elements' is exothermic.
 
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Answers and Replies

  • #2
berkeman
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At least for me, when I first looked at the top graph, my thought was "That's wrong" because I've never really seen arrows pointing the same way on a BE graph like that before. (after looking at the graphs carefully and reading your words, they look accurate to me now, but are still confusing on first glance)

More usually, I'm used to seeing the traditional single BE graph that shows how Fusion and Fission reactions differ, and shows that Fe is the very stable element in the middle of those two regions of the graph. Here is a simple version that I found quickly with Google Images:

https://aggle.blogspot.com/2011/03/fission-and-fusion.html
1566930330778.png


I'm not sure there is a lot of value in talking about "endothermic" nuclear reactions going the opposite directions on the BE graph. Trying to add that into the discussion, especially with students who have not learned a lot yet about nuclear reactions, may not have as much value as just making them familiar with the exothermic nuclear reactions.

My two cents... :smile:
 
  • #3
A M
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Thanks for your reply!
This is almost the last part of my article; before which I've already analyzed BE/A curve and explained exothermic and endothermic processes and how to calculate released/utilizes energy by the difference in final and initial total binding energies (##B_2-B_1##). Then I explained simple definitions of fission and fusion.

The only 'missing' fact was that why they don't always release energy, i.e. why "light nuclei are more fusible and heavy nuclei are more fissionable".
I thought the most understandable explanation would be to elucidate the reason on the graph I've just analyzed and compare them by indicating two arrows in each diagram.

(It is essential to to explain why elements heavier than iron can't be created in star evolution nucleosynthesis or why [α, SF, CD] modes of radioactive decay can't occur in naturally occurring light nuclei.)
 
  • #4
PeterDonis
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Thread closed per OP request.
 

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