1. Physics 213 General Physics Lecture 26

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

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10. 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. 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. 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. 13 Energy Consumption on Earth Oil will last ~ 20-- 50 yrs, given the current rate of consumption of 7 x 10 12 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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15. 15 (Roentgen equivalent man – same biological effectiveness as 1 Rad of x-ray)

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20. 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, 1.007 825 u; neutron, 1.008 665 u; helium, 4.002 602 u; also, 1 u = 931.5 MeV/c 2 ) 20 1.10.7 MeV added 2.10.7 MeV given off 3.28.3 MeV given off 4.0.931 MeV added 5.None of the above, the reaction is not possible due to conservation of energy.

21. 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 = 5 730 years) 21 1.2,640 years 2.17,200 years 3.32,900 years 4.45,800 years 5.60,300 years