Half life and-nuclear_reactions
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This document discusses radioactive decay, half-lives, nuclear fission, and nuclear fusion. It defines half-life as the amount of time it takes for half of a radioactive substance to decay and provides examples of calculating decay based on half-lives. It explains that nuclear fission occurs when a heavy nucleus is split by a neutron, releasing energy and sometimes extra neutrons to continue the chain reaction. Nuclear fusion is when two light nuclei join to form a heavier nucleus, also releasing energy, and this is the process that powers the sun. Both fission and fusion can be used for nuclear energy production and weapons.
Half life and-nuclear_reactions
- 2. Review O We learned that all radioactive atoms eventually decay into stable isotopes. O We did not talk about how long this takes.
- 3. Half-Life O Cannot predict when a radioisotope (RI) will decay. O Can only give probability. O Half-life – Amount of time during which one- half of a radioactive substance will decay. O During a RI’s half-life, every atom has a 50% chance of decaying. O Half-lives can be as short as a fraction of a second or as long as billions of years.
- 4. Half-Lifes O The half-life of 26 Al is 710,000 years. O If you start with 28.0 grams of 26 Al, how much will remain after 1,420,000 years? O At start, 28.0 grams remain. O At 710,000 years, 14.0 grams remain. O At 1,420,000 years, 7.0 grams remain.
- 5. Half-Lifes O The half-life of 61 Fe is 6.0 minutes. How much time must pass before a 600-mg sample decays to 75 mg? O At start, 600 mg remain. O At 6.0 minutes, 300 mg remain. O At 12.0 minutes, 150 mg remain. O At 18.0 minutes, 75 mg remain.
- 6. Half-Lifes O In 48 minutes, 12 mg of 212 Rn will decay to 3 mg. What is the half-life of 212 Rn? O At start, 12 mg remain. O At (1st half-life), 6 mg remain. O At (2nd half-life), 3 mg remain. O It takes 2 half-lives for 12 mg to decay to 3 mg. O 2 half-lives = 48 minutes O 1 half-life = 24 minutes
- 7. Nuclear Fission O A heavy nucleus is struck by a neutron. O It becomes unstable and splits into smaller fragments, releasing energy. O In some cases extra neutrons are also released. O The neutrons can strike other nuclei and cause them to split. O Chain reaction.
- 9. Uses for Nuclear Fission O Nuclear reactors use fission to produce energy.
- 10. Uses for Nuclear Fission O Weapons: the bombs that destroyed Hiroshima and Nagasaki, Japan, were fission bombs.
- 11. Nuclear Fusion O Two light nuclei are joined to produce a larger nucleus. O Energy is released.
- 13. Uses for Nuclear Fusion O Nuclear fusion can be performed at low temperatures, but it does not produce much useable energy. O Fusion only produces significant energy at extremely high temperature and pressure. O The Sun produces energy via nuclear fusion.
- 14. Uses for Nuclear Fusion O Weapons: Thermonuclear (hydrogen) bombs. O Use a conventional fission bomb to trigger nuclear fusion in a lithium hydride shell. O Much more destructive than fission bombs. O Never used in war.