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Why does nuclear fission continue by itself once the process has started?
It doesn't always but it does most of the time and this is because the process is started by firing a particle at the nulcleii of a large atom and if it hits and breaks up the nucleus it hits a new particle is fired from this nucleus to hit another one, thus creating a chain reaction.
A nuclear fission chain reaction of U-235 starts with a slow neutron. What produces this first neutron?
Uranium is naturally radioactive; it's unstable. Somewhere in a sample of uranium, spontaneous fission occurs. All the time. Neutrons are released in this reaction. It cannot be stopped. If critical mass is assembled, a couple of neutrons will appear from a spontaneous fission somewhere within the sample, and a chain will immediately begin to build. There is no way to stop it except by separating the mass into subcritical quantities. But the reaction will do that. It happens in the twinkling of an eye. Always. Note that a so-called fast neutron, a neutron with a lot of kinetic energy, can cause fission. But it has a lot lower probability of doing that than a thermal neutron. Slowing down or "thermalizing" of neutrons increases the chance that they will be captured, and neutron capture will build a chain reaction. This was included because the question stated that a chain starts with a slow neutron, and this might not be the case. It is the slow neutrons that drive the fission chain in nuclear reactors. They have moderators to slow the neutrons down. But the fast neutrons are the chain builders in nuclear weapons. In a nuclear weapon, we don't put moderator material in the thing. We might incorporate some neutron mirrors or lenses in the geometry of the device, but we rely on the a lot of fast neutrons to carry out the mission of burning the fissile material very rapidly to get a big yield. The proof is in the pudding.
Why enormous energy is released during nuclear fission?
Well... It depends on what you mean by "a lot". The binding energy released from a fusion event is actually only about four times that of a fission event, however, the density of the much lighter elements involved in fusion (hydrogen) versus fission (uranium) results in a much more effective total mass to energy ratio, much more than a hundred times that of fission.I'm not talking about delta-mass to energy - that is constant per e = mc2 - I'm talking about the total fuel mass versus the amount of energy available in the reaction.
Is fission always with uranium?
No, fission can occur with other isotopes as well, such as plutonium and thorium. Uranium-235 and plutonium-239 are the most commonly used isotopes in nuclear fission reactions due to their ability to sustain a chain reaction.
What is the source of neutron in nuclear reactor?
Uranium-235 undergoes a small rate of natural spontaneous fission, so there are always some neutrons being produced even in a fully shutdown reactor. When the control rods are withdrawn and criticality is approached the number increases because the absorption of neutrons is being progressively reduced, until at criticality the chain reaction becomes self sustaining. Note that sometimes a neutron source is provided in the reactor, but this is not essential to start the chain reaction, it is to give a shutdown neutron population which is detectable by instruments and so make the approach to critical more observable. The reactor will go critical at the same control rod position whether a source is loaded or not.
What always splits when fission is around?
The nucleus of an atom always splits when fission occurs. Fission is a nuclear reaction in which the nucleus of an atom splits into two or more smaller nuclei.
Why does nuclear fission continue by itself once the process has started?
It doesn't always but it does most of the time and this is because the process is started by firing a particle at the nulcleii of a large atom and if it hits and breaks up the nucleus it hits a new particle is fired from this nucleus to hit another one, thus creating a chain reaction.
When a certain isotope such as Pa-231 is hit by a neutron it will always split into the same smaller nuclei?
false
When a certain isotope such as U 238 is hit by a neutron it will always split into the same smaller nuclei?
No, not at all. Simple decay (alpha decay, beta decay, K capture, etc.) will always produce the same daughter products, but with neutron-induced fission it's ... well, it's not quiterandom, but it's certainly not going to always produce the same products.
What are the pros and cons of nuclear fisson?
There are no pros or cons of nuclear fission, it simply IS. Nuclear fission is a natural phenomena that has always existed, no matter how much one likes or dislikes it.However there are pros and cons to how humans choose to use or not use nuclear fission; the technologies we choose to build with it.
How can nuclear fission be forced to happen?
by a neutron source. nuclear reactors are always started with one to avoid a supercritical power surge from damaging the reactor. nuclear bombs are always triggered by one to make sure the reaction happens at optimal supercriticality for desired yield.
A nuclear fission chain reaction of U-235 starts with a slow neutron. What produces this first neutron?
Uranium is naturally radioactive; it's unstable. Somewhere in a sample of uranium, spontaneous fission occurs. All the time. Neutrons are released in this reaction. It cannot be stopped. If critical mass is assembled, a couple of neutrons will appear from a spontaneous fission somewhere within the sample, and a chain will immediately begin to build. There is no way to stop it except by separating the mass into subcritical quantities. But the reaction will do that. It happens in the twinkling of an eye. Always. Note that a so-called fast neutron, a neutron with a lot of kinetic energy, can cause fission. But it has a lot lower probability of doing that than a thermal neutron. Slowing down or "thermalizing" of neutrons increases the chance that they will be captured, and neutron capture will build a chain reaction. This was included because the question stated that a chain starts with a slow neutron, and this might not be the case. It is the slow neutrons that drive the fission chain in nuclear reactors. They have moderators to slow the neutrons down. But the fast neutrons are the chain builders in nuclear weapons. In a nuclear weapon, we don't put moderator material in the thing. We might incorporate some neutron mirrors or lenses in the geometry of the device, but we rely on the a lot of fast neutrons to carry out the mission of burning the fissile material very rapidly to get a big yield. The proof is in the pudding.
What are some attributes of nuclear fission?
Nuclear fission (as opposed to nuclear fusion) is the process in which a atom is broken into smaller pieces (other smaller atoms). This is different from nuclear decay, in which an unstable particle emits particles in an attempt to become more stable. Nuclear fission can be done on any element, other then hydrogen, however it will not yield energy for anything smaller then Iron. When a large particle, like Uranium, is broken into fissile elements, they don't always break the same way. So you would not always get the same particles. These fissile particles fly off and strike another atom, and break it into pieces and the reaction continues.
Why enormous energy is released during nuclear fission?
Well... It depends on what you mean by "a lot". The binding energy released from a fusion event is actually only about four times that of a fission event, however, the density of the much lighter elements involved in fusion (hydrogen) versus fission (uranium) results in a much more effective total mass to energy ratio, much more than a hundred times that of fission.I'm not talking about delta-mass to energy - that is constant per e = mc2 - I'm talking about the total fuel mass versus the amount of energy available in the reaction.
Does fission or fussion produce radioactive by-products?
The daughter atoms from nuclear fission are nearly always radioactive and nearly always have very short half lives decaying through chains of atoms of short half lives. There is a reason for this. We do not know exactly what the daughter atoms from the fission of a given atom will be, but we do know they will contain all the protons of the parent. The number of neutrons is also preserved, though a few unbound neutrons are usually emitted from the fission. Since atoms with higher atomic numbers can have a greater proportion of protons to neutrons, the daughters usually have far too many neutrons to be stable, and will usually undergo negative beta decay. For example, the fission of 235U might look like this: 92235U --> 3692Kr + 56141Ba + 2n The most massive stable isotope of krypton is 86Kr, so our daughter krypton atom has six too many neutrons to be stable. The decay chain of the 92Kr, given as isotopes and half lives, is as follows, with all decays by negative beta decay: 92Kr 1.8 seconds 92Rb 4.5 seconds 92Sr 2.71 hours 92Y 3.54 hours 92Zr stable The most massive stable isotope of barium is 138Ba, so our daughter has three too many neutrons to be stable. The decay chain of the 141Ba similar to the above is as follows, again all by negative beta decay: 141Ba 18.27 minutes 141La 3.92 hours 141Ce 32.5 days 141Pr stable Most of the daughter decay chains do not produce stable isotopes nearly as quickly as the above, with many having products with half lives of decades to millennia. By comparison, our parent atom, 235U, had a half life of 703,800,000 years.
Is fission always with uranium?
No, fission can occur with other isotopes as well, such as plutonium and thorium. Uranium-235 and plutonium-239 are the most commonly used isotopes in nuclear fission reactions due to their ability to sustain a chain reaction.
How is a uranium-235 nucleus made to undergo fission?
Nuclear fission is the splitting up of big atomic nuclei. Uranium is quite a large nuclei. Each time a uranium atom splits up, it spits out two or three neutrons. One of which might hit another nuclei causing it to split - thus keeping the chain reaction going. The uranium atom - when hit by a neutron splits into Barium and Krypton.
