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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.
When a neutron is shot at a uranium 235 atom the nucleus?
This is the first step of the nuclear fission. Uranium 235 is very unstable but when an extra neutron is added the atom gets aggravated, making the atom burst creating elements and three other neutrons. These three neutrons hit other atoms, starting a very big chain reaction, and finally producing huge amounts of energy.
Where did the first self-substaining nuclear fission chain reaction occur?
The first self-sustaining nuclear fission chain reaction occurred at the University of Chicago's Stagg Field on December 2, 1942, as part of the Manhattan Project. Physicist Enrico Fermi led the team of scientists that successfully achieved this milestone in nuclear physics and engineering.
How does a chain reaction start in chemistry?
In a nuclear fissionchain reaction, neutrons are absorbed by large nuclei, and they undergo fission, part of the fission products are more neutrons, which are absorbed by more nuclei, which ... blah, blah, blah.
What role does neutrons play in fission?
In nuclear fission an atom is broken up into two or more new particles. Sometimes this happens all by itself, but when we want it to happen more rapidly we use a critical assembly of fissile fuel and a moderator, which multiplies the neutron flux. The moderator slows down the neutrons produced in each fission which can then cause further fissions, resulting in a chain reaction. Each fission also releases energy as heat. The chain reaction is controlled at a steady level by control rods which absorb neutrons.
When was fission reaction invented?
The first time a fission chain reaction was produced was in 1942
What did nuclear weapons evolve from?
Nuclear weapons did not evolve! They were invented by people based on newly discovered natural phenomena of the atomic nucleus (e.g. the neutron, fission of heavy nuclei, fusion of light nuclei). The first invention was in 1933 by Leo Szilard while living in London, of the neutron chain reaction. But it took many other inventions before the first atomic fission bombs could be built in 1945 and the first hydrogen fusion bomb in 1952.
How does the uranium and plutonium react in the nuclear reactor?
To set off a fission reaction (the reaction that occurs in a nuclear reactor), a person must first pump a neutron into a heavy nucleus. So if a neutron is pumped into a uranium or plutonium nucleus capable of undergoing fission, the nucleus splits in two, and releases more neutrons, which hit more nuclei, which in turn send out even more neutrons, thus setting off a chain reaction where every time a neutron hits a nucleus, the nucleus splits in two and sends out more neutrons.
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.
When a neutron is shot at a uranium 235 atom the nucleus?
This is the first step of the nuclear fission. Uranium 235 is very unstable but when an extra neutron is added the atom gets aggravated, making the atom burst creating elements and three other neutrons. These three neutrons hit other atoms, starting a very big chain reaction, and finally producing huge amounts of energy.
Why must neutrons in a chain reaction be controlled?
Neutrons in a chain reaction must be controlled to prevent the reaction from reaching a critical mass and becoming uncontrollable. By controlling the rate of neutron production and absorption, engineers can manage the reaction to ensure it remains stable and does not lead to a runaway nuclear event.
Who was the first person to produce a controlled fission reaction?
fermi (the Italian navigator) in 1942 in Chicago
What nuclear reaction provided the massive energy of the atomic bombs dropped on Japan in 1944?
if the atomic bomb had been available in 1944 it would have been used on germany not japan. the first atomic bombs were not built until july 1945, after germany had already surrendered so they were used on japan. nuclear fission in a neutron chain reaction.
Which is more explosive uranium-238 or uranium-235?
Uranium-235 is more explosive than uranium-238. This is because uranium-235 is fissile, meaning it can sustain a chain reaction of nuclear fission, which releases a large amount of energy. Uranium-238 is not fissile and requires a neutron source to undergo fission.
What was the function of graphite in the first atomic reaction?
Graphite was used as a moderator in the first atomic reaction to slow down neutrons released during the fission process. Slowing down the neutrons increases the likelihood of them causing further fission reactions, enabling a self-sustaining chain reaction.
Where did the first self-substaining nuclear fission chain reaction occur?
The first self-sustaining nuclear fission chain reaction occurred at the University of Chicago's Stagg Field on December 2, 1942, as part of the Manhattan Project. Physicist Enrico Fermi led the team of scientists that successfully achieved this milestone in nuclear physics and engineering.
In a nuclear reaction where do the neutron that initially starts the reaction come from Also how does the critical mass matter?
Uranium undergoes spontaneous fission, that is fission that just happens naturally, without any artificial promotion. This occurs in a small proportion of the atoms that decay by alpha activity. It also occurs in plutonium. A completely new reactor with new unirradiated fuel has enough neutrons being formed within it to start a chain reaction, as soon as criticality is achieved. After the fuel has been irradiated, plutonium is also present, initially as 239 but after some time also as 240, which has a greater rate of neutron production, so that the neutron population whilst shutdown would be greater than in a new clean core. Neutron sources may be loaded into the core, and it is often thought these are needed to start the chain reaction. This is not so, the source is there to increase the shutdown neutron population so that instruments can detect it and give the operators warning of approaching criticality. The sources used in UK reactors did not in any case become active until after some irradiation, and the first startups required careful monitoring, but the essential point is that the neutron chain reaction is self starting without any additional neutron source. The reactor has to have a critical mass of uranium (including enough 235) to go critical, when the control rods are withdrawn. In fact there has to be an excess reactivity available because in operation neutron poisons such as Xenon 135 buildup, and there is a negative temperature coefficient. The critical amount of uranium does not however influence the spontaneous fissions, which go on occurring whatever the criticality state of the reactor.
