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Because of the large amount of short-lived fission products, the activity and radiation levels of nuclear fallout decrease very quickly after being released; it is reduced by 50% in the first hour after a detonation, [17] then by 80% during the first day.
The range for significant levels of initial radiation does not increase markedly with weapon yield and, as a result, the initial radiation becomes less of a hazard with increasing yield. With larger weapons, above 50 kt (200 TJ), blast and thermal effects are so much greater in importance that prompt radiation effects can be ignored.
If the aircraft carrying the Hiroshima and Nagasaki bombs had been within the intense nuclear radiation zone when the bombs exploded over those cities, then they would have suffered effects from the charge separation (radial) EMP. But this only occurs within the severe blast radius for detonations below about 33,000 feet (10 km) altitude.
Nuclear scientists and engineers often need to know where neutrons are in an apparatus, in what direction they are going, and how quickly they are moving. It is commonly used to determine the behavior of nuclear reactor cores and experimental or industrial neutron beams. Neutron transport is a type of radiative transport.
Radiation levels in Tokyo on 15 March were at one point measured at 0.809 μSv/hour although they were later reported to be at "about twice the normal level". [203] [204] Later, on 15 March 2011, Edano reported that radiation levels were lower and the average radiation dose rate over the whole day was 0.109 μSv/h. [203]
Compared to a pure fission bomb with an identical explosive yield, a neutron bomb would emit about ten times [9] the amount of neutron radiation. In a fission bomb, at sea level, the total radiation pulse energy which is composed of both gamma rays and neutrons is approximately 5% of the entire energy released; in neutron bombs, it would be ...
By contrast, after a core-collapse supernova, there is an extremely high neutron flux, on the order of 10 32 cm −2 s −1, [4] resulting in nucleosynthesis by the r-process (rapid neutron-capture process). Earth atmospheric neutron flux, apparently from thunderstorms, can reach levels of 3·10 −2 to 9·10 +1 cm −2 s −1.
Neutron radiation is a form of ionizing radiation that presents as free neutrons.Typical phenomena are nuclear fission or nuclear fusion causing the release of free neutrons, which then react with nuclei of other atoms to form new nuclides—which, in turn, may trigger further neutron radiation.