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Final Lecutre Notes on Origin of Neutron_Neutron Source and Neutron Interactions

Final Lecutre Notes on Origin of Neutron_Neutron Source and Neutron Interactions

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Origin of Neutron, Neutron Sources, and Neutron Interactions Lecture Notes The neutron was discovered by Chadwick in 1932. He found that bombardment of Be alphas will generate a radiation that is neutral. He also found that that this same radiation would also knock nitrogen nuclei out of matter. He found that if this radiation was gamma , it had to have an energy of 50 MeV! This did not agree with the available energy from alpha bombardment of Be: Exercise: Show that Chadwick was correct, using alpha, Be interaction. If the reaction is Be ( α, γ ) C; we can calculate the total energy available from this reaction as follows: Chadwick had the following data: M Be = 9.012185 amu; M He = 4.002603 amu; M c-13 = 13.003354 amu m = (9.012185 + 4.002603) - 13.003354 = 0.011434 amu X 931.5 MeV/amu = 10.65 MeV Ö Q = 10.65 MeV Ö Total Energy Available = 10.65 MeV + E alpha = 10.65 + 5 ~ 16 MeV| Chadwick was correct; if the Be (alpha, ?) C generated a gamma radiation, the gamma energy would be 16 MeV; not enough to knock N from matter. Therefore, he concluded that this radiation is a neutral particle which he named Neutron . The characteristics of Neutron are: Mass = 1.0087 amu = 939.57 MeV = 1.6749 X 10 -27 Kg. Categorization of Neutrons Neutron is categorized according to its energy. There a few different nomenclatures used; here is one: Categorization of Neutrons -I Energy (MeV) Neutron Type < 10 -10 Cold 10 -10 to 2.5 X 10 -8 Thermal 2.5 X 10 -8 to 10 -4 Slow 10 -4 to 0.1 Intermediate 0.1 to 100 Fast > 100 Ultra fast
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