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Nuclear Fusion
Nuclear fusion is the phenomenon in which multiple atomic nuclei combine to form a single, larger nucleus. Fusion mostly occurs under extreme conditions, due to the large amount of energy it requires. Thus, examples of fusion tend to be exotic; such as stellar nucleosynthesis, the creation of new elements, and thermonuclear weapons.
521 Questions
What would be the advantages in using nuclear fusion to supply our energy needs in the future?
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The object you describe is a brown dwarf stellar object.
They range in size from 13.5 to 80 times the mass of Jupiter.
They do allow limited deuterium burning in there cores and brown dwarf > 65 Jupiter mass also allow limited lithium fusion but unlike stars do not produce a lot of energy.
Does nuclear fusion occurs as stars cool down?
The star will continue to fuse hydrogen until it runs out of resources and dies out, after which it will collapse and die.
Nuclear fusion powers the Sun. What elemnts in the sun are fused together in the sun?
In the Sun, hydrogen nuclei are fused together to form helium in a process called nuclear fusion. This fusion process releases a large amount of energy in the form of light and heat, which powers the Sun and sustains its brightness.
Describe three advantages nuclear fusion would have over nuclear fission?
1. Unlike fission, during fusion tremendous amount of energy is liberated. Hence fusion of a very small mass generates large amount of energy. 2. Unlike fission the products of fusion reactions are not radio-active. Thus they are harmless and can be replaced easily. 3. Highly penetrating radiations are liberated during fission, which are highly hazardous.
It's A and C. The sun and most other stars are fusion reaction engines, and hydrogen bomb (perhaps more properly a fusion nuclear weapon) apply nuclear fusion to do what they do.
That is called "nuclear fusion".
What is a developing star not yet hot enough to engage in nuclear fusion called?
A protostar.
See related question.
What is the last stage of nuclear fusion?
A neutron star is already a dead star it can produce no more energy, although massively dense it will just continue to radiate its energy out into space until there is nothing left. There is an alternative ending for a Neutron Star and that is, if it was a part of a binary system or had enough mass collect on it could collapse further to create a Black Hole.
Why are the products of nuclear fusion slightly less massive than the reactions?
The products of nuclear fusion are slightly less massive than the mass of the reactants because some of the mass of the reactants is converted into nuclear binding energy to hold the fusion product together.
Where does nuclear fusion occur in the sun and how does it travel to the rest of the solar system?
well it occurs in the core of the sun, and it travels because it is shot out of the sun because it has too much pressure.
What is nuclear fusion and what is the product?
Nuclear fusion is the merging of two atoms into a single atom. All atoms in nature that are heavier than hydrogen have been through fusion at some point.
Energy from nuclear fusion powers the hydrogen bomb. It might also power fusion power plants at some time in the future. In these cases, the products of fusion are helium and neutrons. The neutrons are ionizing radiation, but they have a half life of less than 15 minutes, so they do not last long at all. Some of the neutrons will interact with atoms in the environment, and some of the result will be radioactive isotopes, but these are as unpredictable as the environment in which the fusion takes place, though statistically, these radioactive isotopes mostly also have short half lives.
How nuclear technologies produce enermouse amount of energy?
Nuclear technologies produce enormous amounts of energy through a process called nuclear fission, where the nucleus of an atom is split to release large amounts of heat. This heat is then used to generate steam, which drives turbines connected to generators that produce electricity. The energy released in nuclear reactions is much greater than in chemical reactions, leading to the large amounts of energy produced by nuclear power plants.
When fusion occurs in a star which atoms fuse and what is the resulting atom?
There are several different types of fusion which can occur in stars at different points in their life cycle depending on their mass and metallicity ("metal" means something different to astronomers than it does to most people).
In general, and tremendously simplified, the most common net result of stellar fusion is that one starts with protons (hydrogen nuclei) and ends with alpha particles (helium-4 nuclei). However, there are also (lots of) other things going on, read on if you're interested in more details.
In our own Sun, the most common type of fusion is called the proton-proton chain reaction. In the most common branch of this process, two hydrogen atoms fuse to form deuterium, which fuses with another hydrogen to form helium-3, and then two helium-3 atoms fuse to form helium-4, releasing two hydrogen atoms in the process.
(Note: everywhere I've said "atoms" above I really mean "nuclei"; at the temperatures and pressures required, atoms don't actually exist as independent entities and it's more of a plasma of nuclei and free electrons).
Also, the last step in the process above is called the PPI branch and happens at temperatures of about ten to fourteen million kelvins. At 14-23 MK, the PPII branch is predominant, and involves a helium-3 nucleus fusing with a helium-4 nucleus to form beryllium-7, which then absorbs an electron to form lithium-7, which fuses with a proton (hydrogen nucleus) to form two helium-4 nuclei.
Above 23 MK, the PPIII branch dominates, which again involves fusion of helium-3 and helium-4 to make beryllium-7, which then fuses with a proton to form boron-8, which undergoes beta decay to beryllium-8, which is unstable and immediately splits into two helium-4 nuclei.
There's another branch which has been predicted but never directly observed (PPIV, the fusion of helium-3 with a proton to directly form helium-4). If this does occur in the Sun, it's only in very small amounts (less than about 0.3 parts per million).
In stars more than about 1.3 times the mass of the Sun (and to some extent in less massive stars, including the Sun itself) there's another process called the CNO cycle which has the same net result (protons are consumed and alpha particles are produced). I'm not going to go into the details, because this answer is already long enough, but if you're interested you could look up "CNO Cycle" on, say, Wikipedia.
Heavier nuclei (up to nickel-56) are built by the alpha process. Three alpha particles (helium-4 nuclei) can fuse to form carbon-12 (technically, two first fuse to form beryllium-8, but beryllium-8 is so unstable that unless it immediately fuses with another alpha particle it will just decay back into two helium-4 nuclei again). After that, the elements are built up by the addition of successive alpha particles:
carbon-12 + alpha -> oxygen-16
oxygen-16 + alpha -> neon-20
neon-20 + alpha -> magnesium-24
magnesium-24 + alpha -> silicon-28
silicon-28 + alpha -> sulfur-32
sulfur-32 + alpha -> argon-36
argon-36 + alpha -> calcium-40
calcium-40 + alpha -> titanium-44
titanium-44 + alpha -> chromium-48
chromium-48 + alpha -> iron-52
iron-52 + alpha -> nickel-56
Each of these requires higher and higher temperatures to sustain, so only the highest-mass stars reach this point. Above this the process falls apart, since zinc-60 would be the next product, but this fusion reaction is endergonic (absorbs energy rather than releasing it) and the core of the star collapses instead.
Heat and pressure from the collapse rebounds in a supernova event, which has plenty of energy floating around and can form all kinds of weird heavy nuclei. Supernova explosions are basically the source of all nuclei heavier than nickel.
What substances does nuclear fusion use?
Experiments in fusion have used deuterium and tritium, both isotopes of hydrogen
How do nuclear fusion differ fundamentally from nuclear fission?
Nuclear fusion doesn't produce energy.
Why does nuclear fusion not occur on earth?
Because the conditions of temperature and pressure that occur in stars do not occur on earth
How does a nuclear reaction take place?
First nuclear reactions always involve the nucleus and except for K capture beta decay never involve any of the electrons around the nucleus.
There are seven different types of ordinary nuclear reactions:
- fission, a massive nucleus splits into two lighter fragment nuclei (about 1/3 & 2/3 the mass of the original nucleus) and several free neutrons, fission can happen spontaneously in some isotopes (e.g. plutonium-240) but is usually triggered by the capture of a neutron, as fission always produces free neutrons it is possible to produce a neutron chain reaction to keep the process going
- fusion, light nuclei join forming a heavier nucleus, this reaction can only happen under conditions of very high temperature and pressure (causing the nuclei to be fully ionized, traveling at high velocity, and pressed tightly together) it is very hard to to get started and keep going (except deep inside stars) Note that fusion is the only one of these seven nuclear reactions that is affected in any way by the temperature or pressure of the environment it happens in
- alpha decay, a nucleus spontaneously ejects a helium nucleus (i.e. alpha particle)
- beta- decay, a neutron in the nucleus spontaneously transforms into a proton and the nucleus ejects an electron and an electron antineutrino
- beta+ decay, a proton in the nucleus spontaneously transforms into a neutron and the nucleus ejects an positron and an electron neutrino
- K capture beta decay, a proton in the nucleus spontaneously transforms into a neutron and the nucleus captures an electron from the innermost (i.e. K) electron shell and ejects an electron neutrino
- gamma decay, a nucleus in a metastable (i.e. excess energy) state spontaneously relaxes its proton and/or neutron shells to a lower energy state and ejects a gamma photon with an energy equal to the energy lost in the nucleus
However if you include other subatomic particles not present in ordinary matter (e.g. muons, antimatter particles, strange particles) a much wider and more confusing variety of nuclear reactions can happen that are beyond the scope of the original question. I will only mention one of these nuclear reactions: muon catalysed cold fusion. This is interesting because it permits the fusion nuclear reaction to happen at ordinary room temperature.
In muon catalyzed cold fusion the electrons around hydrogen nuclei are replaced with muons (particles identical to electrons in every way except that they have 200 times the mass), being much more massive than electrons their orbitals are much smaller. So much smaller that the nuclei can come close enough to each other at ordinary room temperature that the nuclei can fuse! The fusion energy release causes the product nucleus to lose its muons and become ionized. This process is called "muon catalyzed" because these free muons can now replace electrons around fresh hydrogen nuclei, repeating the nuclear reaction over and over without requiring any additional muons. The only problem with muon catalyzed cold fusion is that the muons required to begin this nuclear reaction are very expensive to produce.
No. In a fusion reaction, a heavier element is made of a lighter pair by "gluing" them together in a fusion reaction. When we split an atom, that's called atom splitting, or sometimes fission, not fusion. They are opposites. Stars give off light, but the primary fuel in their fusion engines is hydrogen, which they convert into helium. As the hydrogen burns out, the star begins making helium into carbon.
What is the resulting nucleus if a tritium and a deuterium nuclei fuse?
Helium and a neutron:
D + T --> He + n + 17.59 MeV
What does E equals mc2 have to do with nuclear fusion?
Some mass is "lost" during nuclear fusion and E = mc2 gives the amount of energy that this "lost" mass will be equal to.
