Physics 213 General Physics Lecture 26

2 Last Meeting: Nuclear Physics I Today: Nuclear Physics II, Applications Practice Problems

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10 Fusion in the Sun All stars generate energy through fusion The Sun, along with about 90% of other stars, fuses hydrogen Some stars fuse heavier elements Two conditions must be met before fusion can occur in a star The temperature must be high enough The density of the nuclei must be high enough to ensure a high rate of collisions

11 Proton-Proton Cycle The proton-proton cycle is a series of three nuclear reactions believed to operate in the Sun Energy liberated is primarily in the form of gamma rays, positrons and neutrinos 2 1 H is deuterium, and may be written as 2 1 D

12 Fusion Reactors Energy releasing fusion reactions are called thermonuclear fusion reactions A great deal of effort is being directed at developing a sustained and controllable thermonuclear reaction A thermonuclear reactor that can deliver a net power output over a reasonable time interval is not yet a reality

13 Energy Consumption on Earth Oil will last ~ yrs, given the current rate of consumption of 7 x J/s. Coal will last hundreds of years. Uranium (fission) will last thousands of years. Deuterium (fusion) will last hundreds of million of years. Solar energy (?) will last billions of years.

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What energy must be added or given off in a reaction where two hydrogen atoms and two neutrons are combined to form a helium atom? (Atomic masses for each: hydrogen, u; neutron, u; helium, u; also, 1 u = MeV/c 2 ) MeV added MeV given off MeV given off MeV added 5.None of the above, the reaction is not possible due to conservation of energy.

If a fossil bone is found to contain 1/8th as much Carbon ‑ 14 as the bone of a living animal, what is the approximate age of the fossil? (half ‑ life of 14 C = years) ,640 years 2.17,200 years 3.32,900 years 4.45,800 years 5.60,300 years