11 ms·
If you look at the mass before of their fuel, 1 deuterium atom + 1 tritium atom: 2.01410177811 u + 3.01604928 u = 5.03015105811 u vs the mass of the fusio
by spullara 4y ago
If you look at the mass before of their fuel, 1 deuterium atom + 1 tritium atom:
2.01410177811 u + 3.01604928 u = 5.03015105811 u
vs the mass of the fusion products of 1 helium atom and 1 neutron:
4.002602 u + 1.008 u = 5.010602 u
You'll notice that even though we started with 5 neutrons and 2 protons and ended up with the same number there was some additional binding energy that is unaccounted for in the new configuration. This is the energy released by the fusion reaction via E = mc^2. Here we see the mass difference is:
5.03015105811 u - 5.010602 u = 0.01954905811 u
Converting that to energy you find that is 17.6 MeV. As you go up the periodic table fusing nuclei you will get less and less marginal energy until you get to iron where at that point fusion become net negative and fission is then takes over where breaking nuclei apart gains energy, marginally more as you go up the periodic table. That's why you want to fuse light particles and fission very heavy particles. It is also why there is so much iron as it is kind of the base state of both of these reactions.
- aaroninsf 4y agoThis is an A+ comment—helpful, well-formatted, concise, with bonus interesting additional detail. Thank you.
- eklitzke 4y agoTangentially related, but I think this is an interesting fact, all the atoms in our universe/galaxy/solar system with a mass up to that of iron are formed in the core of stars in stellar fusion. Hydrogen fuses into helium, and as a star nears the end of its lifetime you get heavier elements like lithium, carbon, and so on. Under normal stellar fusion no elements heavier than iron will be produced, and iron is only element number 25. If you just looked at nucleosynthesis through the lens of stellar fusion, it isn't obvious that there should be any heaver-than-iron atoms at all in the universe. These heaver-than-iron elements are created in a very interesting and exotic process. When a large enough star dies it explodes in a supernova, and a huge amount of energy and neutrons are released in a very short period of time. This supernova generates enough energy and neutron material that small amounts of heavier elements like gold, platinum, etc. are created through exotic nuclear fusion reactions, even though these heavy fusion reactions are energy-absorbing. It's interesting to think when you're wearing jewelry made from gold or platinum, all of those atoms in your jewelry were created during the death of a star.
- b33j0r 4y agoIt’s funny that alchemy was kinda onto something, but underestimated the energy requirements by orders of magnitude of orders of magnitude
- BizarroLand 4y agoTrue, all you need to turn lead into gold is a moderately powerful collider and some hydrogen. The conversion is also very slow. And expensive. To make it this way it would cost a Quadrillion dollars an ounce. https://www.scientificamerican.com/article/fact-or-fiction-lead-can-be-turned-into-gold/ https://www.scientificamerican.com/article/fact-or-fiction-l...
- unnouinceput 4y agoQuadrillion now, but costs will drive down and once is turned to gold, it stays gold. In the far future where all gold was mined this will be the only process left to get more. Or explode stars and capture gold from them.
- riemannzeta 4y agoGreat comment. But you meant 2 helium atoms and 1 neutron in the second equation, correct?
- spullara 4y agoNope. Helium has 2 protons and 2 neutrons. Here is an image that shows the reaction: https://www.energy.gov/sites/default/files/styles/full_article_width/public/2020/05/f74/gpawg-fusion-reactions.jpg?itok=JhUKmSy2 https://www.energy.gov/sites/default/files/styles/full_artic...
- subsubzero 4y agoDo we know how much tritium is needed for a city's energy generation? What about a state etc? Reason I ask is the only uses I have seen for tritium is on old watch dials made in the pre-90's. Curious how much of this resource is out there.
- S04dKHzrKT 4y agoReal Engineering recently made a video that covers fuel needs. https://www.youtube.com/watch?v=BzK0ydOF0oU https://www.youtube.com/watch?v=BzK0ydOF0oU
- phtrivier 4y agoAnd the (otherwise excellent) channel is supposed to soon post an adv... I mean informer... I mean "exclusive documentary" about "repeat after me we're totally not a scam - we just play one on YouTube" fusion startup Helion. Which I'm going to watch, because even though everything I hear about this company gives me insane Theranos vibes... Well, if they pull it off... They might light a bulb with fusion in my lifetime.
- adaml_623 4y agoThe Helion approach seems plausible to me. Can you point me towards some of the sources that give you vibes?
- phtrivier 4y agoA recent episode on Matt Ferrel's Undecided [1] (And I though I had seen a similar segment on "Answer with Joe", but I can't find it.) None of those would be opposable source, of course - there won't be any until they open a plant, publish data, etc... In the meantime, I see a hype cycle brewing, and it makes me a bit uncomfortable - but, we'll see. [1] https://youtu.be/yNP8by6V3RA https://youtu.be/yNP8by6V3RA
- twic 4y agoTake spullara's numbers: 2.01410177811 u = 3.34449439340696e-24 g deuterium 3.01604928 u = 5.008267217094e-24 g tritium 17.6 MeV = 7.832863e-19 kWh energy Divide through, and you will see that you need 4.27 ug/kWh of deuterium, and 6.39 ug/kWh of tritium. A random source [1] says that New York will use 50.6 TWh per year by 2027. That would require ~216 kg/yr of deuterium and ~323/yr kg of tritium. This is all assuming 100% efficiency. A quick read suggests 50% efficiency might be practical, so double those quantities. Also, i could easily have messed up that calculation somewhere, so please do check it! [1] https://www.buildingcongress.com/advocacy-and-reports/reports-and-analysis/Electricity-Outlook-2017-Powering-New-York-Citys-Future/The-Electricity-Outlook-to-2027.html https://www.buildingcongress.com/advocacy-and-reports/report...
- joe-collins 4y agoAnd on a total tangent, this fact played a part in worldbuilding done by the author L. E. Modesitt, Jr. > When I initially decided to write The Magic of Recluce in the late 1980s, I'd been writing science fiction exclusively... I conveyed a certain dismay about the lack of concern about economic, political, and technological infrastructures in various fantasies then being written and published in the field... > I faced the very real problem of creating a magic system that was logical... Most fantasy epics have magic systems. Unfortunately, many of them, particularly those designed by beginning authors, aren't well thought out, or they're lifted whole from either traditional folklore or gaming systems and may not exactly apply to what the author has in mind. > I began by thinking about some of the features and tropes of traditional fantasy. One aspect of both legend and folklore that stuck out was the use of "cold iron" to break faerie magic, even to burn the creatures of faerie, or to stand against sorcery. Why iron? Why not gold or silver or copper? Not surprisingly, I didn't find any answers in traditional folklore or even contemporary fantasy. Oh, there were more than a few examples, but no real explanations except the traditional ones along the lines of "that's just the way it works." > For some reason, my mind went back to astronomy and astrophysics and the role that nuclear fusion has in creating a nova... Each of these fusion reactions creates a heavier element and releases energy... The proton-proton reaction that produces iron, however, is different, because it is an endothermic reaction... > At the same time, the fact that metals such as copper or silver conducted heat and electrical energy suggested that they were certainly less than ideal for containing electrical energy. Gold and lead, while far heavier than iron, do not have iron's strength, and other metals are too rare and too hard to work, particularly in a low-tech society. > At this point, I had a starting point for my magic system. I couldn't say exactly what spurred this revelation, but to me it certainly made sense. Iron can absorb a great amount of heat. If you don't think so, stand on an iron plate barefoot in the blazing sun or in the chill of winter. Heat is a form of energy. In fantasy, magic is a form of energy. Therefore, iron can absorb magic and, by doing so, bind it. https://www.lemodesittjr.com/the-books/saga-recluce/recluce-tales/ https://www.lemodesittjr.com/the-books/saga-recluce/recluce-...
- infogulch 4y ago> It is also why there is so much iron as it is kind of the base state of both of these reactions. I always thought this is the interesting takeaway, both fusion and fission funnel their constituent matter towards iron, as the final stable state of matter. Far future civilizations will have a lot of iron on their hands.