Nuclear physics Bombs, power plants
Radioactive decay • Requires a metastable nucleus, such as 238 U.
Radioactive decay • Requires a metastable nucleus, such as 238 U. • 238 U is essentially 234 Th + 4 He (a particle).
Radioactive decay • Requires a metastable nucleus, such as 238 U. • 238 U is essentially 234 Th + 4 He (a particle). • Because of q. m. , a has a wave function
Radioactive decay • Requires a metastable nucleus, such as 238 U. • 238 U is essentially 234 Th+ 4 He (a particle). • Because of q. m. , a has a wave function • Decay occurs by tunneling.
Half life • Any radioactive nucleus can decay at any moment. • Half life is related to probability: – Low prob. -> long half life – High prob. -> short half life
Decay examples Half-life is the time it takes half the material to decay. Carbon used for dating (formerly) living things.
Where do the elements come from?
Stability diagram Heavy elements can fission into lighter elements. Elements from helium to iron were manufactured in the cores of stars by fusion. Heavier elements are metastable and were made during supernovae explosions. Light elements can undergo fusion into heavier elements.
Uranium decay sequence (one path)
Uranium decay sequence (one path) Radon is the first isotope in the sequence that is a gas. Uranium occurs naturally in the soil around here, but is not a direct problem because the soil shields the alphas. However, radon, being a gas, rises into our homes causing lung cancer.
Fission • Hitting a radioactive nucleus with a neutron cause it to split into several pieces: FISSION. Energy is released. • If you have enough, chain reaction!
Chain reaction For reaction to be self-sustaining, must have CRITICAL MASS.
Fission bomb
Nuclear reactors
Risks of nuclear power • Reactor explosion
Risks of nuclear power • Reactor explosion
Risks of nuclear power • Reactor explosion • Radiation release from plant. • Storage – Leakage • inert ceramics fix – Inadvertent entry • Terrorist threat
Risks of nuclear power • Reactor explosion • Radiation release from plant. -- TMI • Storage – Leakage • inert ceramics fix – Inadvertent entry We do not have to worry about • Terrorist threat reactor fuel stolen for bombs, because • Processing accidents it is not sufficiently enriched.
Tokaimura, Japan September 28, 1999 • Japan’s nuclear industry’s first critical accident. • Inadvertent critical mass • Container size: 16 kg instead of 2. 4 • Container shape 10 liters 16 kg Two of three workers died within seven months.
How safe is nuclear power? • Nuclear power’s track record shows it is among safest energy sources. – Wind and hydroelectric are limited. – Coal is dangerous (pollution kills). – Solar would require huge construction, with accompanying construction accidents.
Can we make it safer? • Yes! – Better training and on-site monitoring by agents paid by government, not power companies. – In the event of accident, can almost completely eliminate radiation danger with iodine tablets. Buy your own!
Advantages of nuclear power • No pollution (except thermal, like any heat engine) • No lung cancer, emphysema, etc. • No greenhouse effect • Fewer mining accidents than coal.
Fusion • Light nuclei more stable when combined. • Tremendous energy release. • Hydrogen bombs • Fusion power?
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