S10P1CLec29A

# S10P1CLec29A - Physics 1C Lecture 29A"Nuclear powered...

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Physics 1C Lecture 29A "Nuclear powered vacuum cleaners will probably be a reality within 10 years. " --Alex Lewyt, 1955

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The Nucleus All nuclei are composed of protons and neutrons (they can also be called nucleons). The atomic number, Z, is the number of protons in the nucleus. The neutron number, N, is the number of neutrons in the nucleus. The mass number, A, is the number of nucleons in the nucleus (A = N + Z). In symbol form, it is: X A Z where X is the chemical symbol of the element.
The Nucleus Isotopes of an element have the same Z but differing N (and thus A) values. For example, both have 92 protons, but U-235 has 143 neutrons while U-238 has 146 neutrons. Nucleons and electrons are very, very small. For this reason, it is convenient to define a new unit of mass known as the unified mass unit, u. Where: 1 u = 1.660559x10 -27 kg 92 235 U 92 238 U

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The Nucleus Einstein’s mass-energy equivalence tells us that all mass has an energy equivalence. This is known as rest energy. This means mass can be converted to forms of useable energy. The equation is given by: From here we get the energy equivalence of 1u of mass would be: E R = mc 2 E R = 1 u ( ) c 2 = 1.492431 × 10 10 J = 931.494 MeV This gives us the relationship between mass and energy to also be: 1 u = 931.494 MeV c 2
The Nucleus This gives us the following masses for the elementary nuclear particles: Note that the neutron is slightly heavier than the proton.

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