Questions tagged [fusion]

The fusion tag is used for questions about nuclear fusion, both the basic process at a physical level and it's use as a potential energy source.

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98
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4answers
32k views

Would a pin head heated to 15 million degrees Celsius kill everyone in a 1000 mile radius?

The YouTube video How Hot Can it Get? contains, at the 2:33 mark, the following claim: A pin head heated to 15 million degrees will kill everyone in a 1000 miles radius. On what basis can this ...
96
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11answers
15k views

Why do fusion and fission both release energy?

I only have high school physics knowledge, but here is my understanding: Fusion: 2 atoms come together to form a new atom. This process releases the energy keeping them apart, and is very energetic. ...
75
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3answers
14k views

Why didn't the Big Bang create heavy elements?

In the case of a supernova explosion it is possible to create heavy elements through fusion. Supernovae have a tremendous amount of energy in a very small volume but not as much energy per volume as ...
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10answers
31k views

Can Jupiter be ignited?

Our solar system itself contains two candidate "Earths" One is Jupiter's moon Europa and another is Saturn's moon Titan. Both of them have the problem of having at low temperature as Sun's heat ...
41
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3answers
11k views

What stops us from creating a nuclear fusion reactor as we already have the hydrogen bomb working on the same principle of fusion?

I have been out of physics for some time now since my childhood, so please bear with me if the question below feels too novice. I grew up with the understanding that the nuclear fusion reaction is ...
35
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3answers
4k views

Nuclear Fusion: Why is spherical magnetic confinement not used instead of tokamaks in nuclear fusion?

In nuclear fusion, the goal is to create and sustain (usually with magnetic fields) a high-temperature and high-pressure environment enough to output more energy than put in. Tokamaks (donut shape) ...
32
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3answers
24k views

Origin of elements heavier than Iron (Fe)

In all the discussions about how the heavy elements in the universe are forged in the guts of stars and especially during a stars death, I usually hear that once the star begins fusing lighter atoms ...
31
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1answer
3k views

Using nuclear devices to terraform Mars: Elon Musk's nuclear proposal? [closed]

Elon Musk has recently suggested Using nuclear devices to terraform Mars. In the past, comet related ideas were mooted, but Musk seems, to me anyway, to be a man in a hurry and perhaps his idea has ...
25
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3answers
20k views

Why is the nucleus of an Iron atom so stable?

Lighter nuclei liberate energy when undergoing fusion, heavier nuclei when undergoing fission. What is it about the nucleus of an Iron atom that makes it so stable? Alternatively: Iron has the ...
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6answers
7k views

Is fission/fusion to iron the most efficient way to convert mass to energy?

Is fission/fusion of any element to iron-56 (or nickel-62?) the best way to convert mass to energy, that doesn't involve black holes? In other words, will we be always limited to convert only about 1%...
22
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1answer
3k views

Why is a stellarator-type nuclear fusion reactor so oddly-shaped?

My first impression: It's a mess. Why is it shaped like that? I can't find any info about its shape other than it's a special arrangement of magnetic coils.
22
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1answer
3k views

When will hydrogen no longer be the most abundant nucleus?

In a recent question, we learned why hydrogen is currently the most abundant nucleon or element in the universe. Here I ask a follow-up: For how long will hydrogen be the most abundant nucleus? It ...
22
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2answers
3k views

When did the first carbon nucleus in the Universe come into existence?

I am a chemist with a passion for astrophysics and particle physics, and one of the most marvellous things I have learned in my life is the process of stellar nucleosynthesis. It saddens me how my ...
19
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3answers
4k views

How do fusion reactors deal with blackbody radiation?

The plasma of the ITER reactor is planned to be at 150 million K. Using the Stefan-Boltzmann law, setting the surface area as $1000\,\mathrm{m}^2$ (the plasma volume is $840\,\mathrm{m}^{3}$ so this ...
19
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4answers
2k views

Does 60kg of fusion fuel produce as much energy as 400 kilotonnes of coal?

Several people, including Fusion for Energy have posted this infographic: To meet the energy needs of a city of 1 million people one would need: Either 250,000 tonnes of oil Or 400,000 ...
18
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2answers
2k views

Why is D-T fusion easier than T-T?

At a very basic level, fusion can occur when the electrostatic repulsion between nuclei is overcome and they approach close enough for the strong force to come into play. Thus, the easiest reactions ...
18
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1answer
1k views

Why all the orifices, protuberances, hinged/bolted panels, etc. on a stellarator?

My question was inspired by this one - in particular the image it has (also shown here): Why does the external casing of the Stellarator (in particular, the Wendelstein 7-X shown in the above image) ...
17
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2answers
929 views

Is there a sound theoretical argument against inner-shell induced nuclear chain reactions?

There is a claim often made about cold fusion, that it is excluded theoretically. The main theoretical argument is that electronic energies are too low to overcome the Coulomb barrier, since d-d ...
16
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1answer
2k views

Can nuclear fusion alone account for the energy output from type 1a supernova?

Unlike other supernova, which can vary in their size, Type Ia supernova are all about the same size. This is due to the fact that they are caused when a white dwarf star gains enough mass from its ...
16
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1answer
805 views

Do supernovae produce an appreciable amount of lithium?

David Z's answer to this question got me wondering - is any appreciable amount of lithium produced as the result of a supernova explosion, either by fusion (which seems unlikely to me, but I don't ...
15
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3answers
11k views

What would be the characteristics of Jupiter if it shrank?

So, I've heard from various works of science fiction about the prospect of turning Jupiter into a star. From what I know about the physics of such a task, it would require somehow condensing Jupiter ...
14
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2answers
982 views

How large can you make a tokamak?

I've seen questions on how small you can make a tokamak. But I haven't yet seen any "physical" upper limit on the tokamak design. If you take a wind turbine for example, doubling the linear ...
14
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2answers
425 views

How long does a positron last in the Sun's core?

Kicking off of this question, I have a short follow-up. The fusion of hydrogen into helium in the Sun's core requires the emission of two positrons per final helium nucleus, because we start off with ...
13
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2answers
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How exactly is fusion possible?

It is a very dumb question but, I once read that fusion was possible when the wavefunction that describes the position of a particle overlaps with the wavefunction of other particle, but I think I don'...
13
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4answers
53k views

Where does the energy produced by fusion come from?

Fission, in layman's (or "initiate's") terms, is easy enough to understand; a large atom with a lot of protons and neutrons requires a large amount of force provided by the strong interaction to ...
13
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3answers
3k views

Nuclear fusion: what causes this “resonance” peak?

Can anyone explain why the $^{11}\mathrm{B}\mathrm{H}$ fusion cross-section has a peak near 150 keV, and why $\mathrm{D}\mathrm{D}$ and $\mathrm{D}\mathrm{T}$ have no such sharp peaks?
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3answers
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How often does nuclear fusion occur within the human body?

I'm just curious. I figure atoms fuse occasionally just by chance, like quantum tunneling or rogue waves. Is this true? If so, any idea how often?
13
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2answers
2k views

Hydrogen as a fuel in Sun

The source of Sun's incessant energy is hydrogen; which is continuously converting to helium through nuclear fusion reaction releasing energy. Why does not all hydrogen convert into helium in one big ...
12
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3answers
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Why can't Iron fusion occur in stars?

It is said that iron fusion is endothermic and star can't sustain this kind of fusion (not until it goes supernova). However star is constantly releasing energy from fusion of elements like Hydrogen ...
12
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4answers
9k views

Could we use particle colliders as fusion generators?

So I know the basic gist is that fusion power's main issue is sustaining the fusion. I also know that there are two methods. The Torus method and the laser method. The torus magnetically contains ...
12
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1answer
3k views

Is an H bomb a better “fusion reactor” than the Sun's core?

A few days ago I asked about a fusion reactor design I was thinking about and got a well-founded answer by #BowlOfRed#. There is the question I posted: Another cold-fusion reactor scheme :) Is it ...
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3answers
6k views

Why does fusion stop at iron when nickel is most tightly bound?

My understanding is that stellar fusion naturally stops at iron because it is energetically unfavourable to grow the nucleus further. But iron is only the third most tightly-bound nucleus, nickel is ...
12
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2answers
3k views

With what probability does nuclear fusion occur at energies far below the Coulomb barrier?

Even at the core of the sun, the temperature of $\sim 10^7$ K only results in $kT\sim1$ keV, which is about a thousand times less than the electrical potential energy of $\sim1$ MeV needed in order to ...
11
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3answers
2k views

Proton - neutron fusion?

In reviewing some problems in an elementary book, I ran across a reference to the reaction $p+n\rightarrow d$ + "energy". Is that possible? I don't see any reason why not, but I don't find any ...
11
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5answers
3k views

What are the challenges to achieving cold fusion?

I am an absolute neophyte regarding physics. What are the challenges to achieving cold fusion? I'm not sure this is a duplicate of Why is cold fusion considered bogus?, because that question is ...
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2answers
8k views

Why is Helium-3 better than Deuterium for fusion energy production?

I see that many websites and magazines with physics thematic are pretty excited about mining Helium 3 isotope on the Moon. But this seems to be a very hard-to-get resource. For more than one reason: ...
11
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3answers
1k views

Concentrating Sunlight to initiate fusion reaction

The idea is to collect sunlight over a large area, and concentrate it down to the nano scale. For the sake of discussion lets say you concentrate all the light you collect down to 1000 nanometers (1µm)...
10
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2answers
2k views

Does converting rest mass to energy instantly change the gravitational attraction it exerts?

Let there be two hydrogen atoms having 1.1 mass each. We use solar fusion to convert the two hydrogen plasma to helium with a mass of 2 and 0.2 gamma radiation. Before the fusion process gravity was ...
10
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2answers
4k views

Nuclear Fusion with extremely high pressure and low temperature

Theoretically, if we just create a high pressure with low (room 20C) temperature, at some point nuclear fusion can be started. Is there any research on this topic, how high should be this pressure ...
10
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2answers
10k views

How to explain $E=mc^2$ mass defect in fission/fusion?

What is the nature of nuclear energy? This is closely related to the correct explanation of mass defect. I did some research of that topic and cannot come to a single comprehensive and consistent ...
10
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3answers
12k views

Can open, unsafe nuclear fusion reaction burn the atmosphere?

I happened to hear people saying that the nuclear fusion bomb tests could set the atmosphere on fire. I have some serious doubts about that - but I have no facts. Nuclear fusion reaction requires $15*...
10
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1answer
475 views

Does tritium hydride exhibit measurable spontaneous fusion via proton tunneling?

In a fascinating 30 June 2013 article in Nature Chemistry, researchers from the University of Leeds found that when molecules of hydroxyl (OH, a fairly stable radical) and methanol (CH$_3$OH) are cold ...
10
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1answer
118 views

How many times do solar protons repeatedly fuse and fission before they form deuteron

In the proton-proton chain reaction in the Sun, the first step is $$p + p \rightarrow \; ^2_2{\rm He} .$$ After this, the most likely thing to happen next is that the reverse reaction occurs: the $^...
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1answer
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How does our sun create positrons in it?

How does our sun create positrons? And does the sun emit said positrons after their creation? I read that the sun creates positrons at it's center but I couldn't find how they form. Is it a ...
9
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3answers
337 views

Magnetic confinement in a tokamak

I have a question about why exactly the twisting of the field lines in a Tokamak solves the magnetic confinement issue. My understanding is that the magnetic confinement issue arises in the toroidal ...
9
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3answers
852 views

Nuclear fusion scaling with reactor size

Thinking about the physics of thermonuclear fusion, I have always had an intuitive sense that making fusion feasible is matter of reactor size. In other words I feel like: If the fusion reactor is ...
9
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2answers
1k views

Why more Fe-56 than Ni-62 as fusion product in heavy stars?

Suppose we create an Fe-56 nucleus and an Ni-62 nucleus, each from individual protons and neutrons. In the case of Ni-62, more mass per nucleon is converted to binding energy. Thus we could argue the ...
9
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3answers
1k views

Nuclear fusion : ion vs atom fusion cross section?

I've read critique on ITER project (in Russian), and one of points was that cross section of ion-ion fusion is much lower than ion-atom and atom-atom, and that's the reason why it likely to not work. ...
8
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5answers
2k views

What new breakthrough energy technologies are close to being realized? [closed]

Energy production is one of the burning issues for humankind. There has been some talk about future energy technologies including Fusion, Anti-matter annihilation and Zero-point-energy (from most to ...
8
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3answers
13k views

Why only light nuclei are able to undergo nuclear fusion not heavy nuclei?

Is it because of the binding energy or the binding energy per nuclei . I am having trouble with this whole binding energy and nuclear fusion concept.