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Some atoms, notably uranium-238, do not usually undergo fission when struck by slow neutrons, but do split when struck with neutrons of high enough energy. [1] The fast neutrons produced in a hydrogen bomb by fusion of deuterium and tritium have even higher energy than the fast neutrons produced in a nuclear reactor. This makes it possible to ...
The remaining energy to initiate fission can be supplied by two other mechanisms: one of these is more kinetic energy of the incoming neutron, which is increasingly able to fission a fissionable heavy nucleus as it exceeds a kinetic energy of 1 MeV or more (so-called fast neutrons). Such high energy neutrons are able to fission 238
The BN-350 fast-neutron reactor at Aktau, Kazakhstan.It operated between 1973 and 1994. A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV, on average), as opposed to slow thermal neutrons used in thermal-neutron reactors.
They are named fast neutrons to distinguish them from lower-energy thermal neutrons, and high-energy neutrons produced in cosmic showers or accelerators. Fast neutrons are produced by nuclear processes: Nuclear fission: thermal fission of 235 U produces neutrons with a mean energy of 2 MeV (200 TJ/kg, i.e. 20,000 km/s), [11] which qualifies as ...
For "thermal" (slow-neutron) fission reactors, the typical prompt neutron lifetime is on the order of 10 −4 seconds, and for fast fission reactors, the prompt neutron lifetime is on the order of 10 −7 seconds. [16] These extremely short lifetimes mean that in 1 second, 10,000 to 10,000,000 neutron lifetimes can pass.
In most fission reactor designs, the nuclear fuel is not sufficiently refined to absorb enough fast neutrons to carry on the chain reaction, due to the lower cross section for higher-energy neutrons, so a neutron moderator must be introduced to slow the fast neutrons down to thermal velocities to permit sufficient absorption.
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A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (1.6 × 10 −13 J), hence a speed of ~ 14 000 km/s (~ 5% of the speed of light). They are named fission energy or fast neutrons to distinguish