Where do elements heavier than iron come from?

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willpittenger

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Iron is the heaviest element that can be created by stellar fusion. So where do elements like uranium come from? <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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Saiph

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elements lighter than iron are the only elements that produce energy when fused. Iron, and heavier elements, have a net energy <i>loss</i> during fusion. <br /><br />This doesn't mean they can't be fused...it just requires an excess amount of energy, as you can't fuse them in a chain reaction (chain reactions require a net gain in energy per reaction sequence).<br /><br />Heavier elements are thus formed when stars are in phases that have an excessive amount of energy...helium and carbon flashes would be good examples. Problem is, those heavier elements are locked up near the site of fusion, the core.<br /><br />Along comes a supernova, which blows the star to bits (if it's large enough), and should spread the stuff willy-nilly.<br /><br />But there's one last problem: To much energy (light) can actually break the nuclei apart, via photo-dissociation. During a supernova, there is so much energy that everything is really reduced to hydrogen and helium again.<br /><br />So...we're back to square one.<br /><br />Except...the supernova event itself is a phase with ludicrious amounts of energy. This heats up lots of material, we've got lots of high pressure zones due to shockwaves, and a very large amount of heavy nuclei are fused during the supernova event itself (just not near the energy saturated central regions). <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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bbrock

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As usual, Saiph has answered the question so well, that the rest of us can only learn from it. <br /><br />Good Question and Great Answer. <br /><br />Bill
 
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