WS Nuclear reaction Worksheet Answer Key 3. 208 Pb (product side) 82 0 e − 1 (reactant side) 256 Md (product side) 101 4. 214 Pb (product side) 82 1. 2. 6. 12 C 6 (product side) 0 e − 1 (reactant side) 7. 4 He (product side) 2 5. 0 8. − 1 e (reactant side) 210 Po →4 He+ 206 Pb st 2 82 9. 1 alpha decay: 84 206 Pb →4 He+ 202 Hg nd 2 80 2 alpha decay: 82 210 Pb → 0 e+ 210 Bi −1 83 10. 82 11. I will not go through each step, however your final answer should be bismuth – 208. There was a typo in the question – if you used thorium – 238 as your starting material instead of thorium – 232, the final stable isotope is bismuth – 214. Unfortunately bismuth – 214 is very unstable with a half life of only about 20 minutes. 12. 0.125 mg 3 half lives passed (30 years x 3 = 90 years), so 1/2= 0.5, 0.5/2 = 0.25, .25/2 = 0.125mg 13. 2016 2 half lives passed (2.5/2=1.25, 1.25/2=0.625) each of which is 28 years. Add 56 years to 1960, and the year will be 2016 when only 0.625 g remains. 14. 25 mg 2 half lives passed (29 hours x 2 = 58 hours), so 100/2 = 50, 50/2 = 25. 15. 1.0 mg 2 half lives passed (6 days and 2 hours is 146 hours, and 73 x 2 = 146), so 4.0/2 = 2.0, 2.0/2 = 1.0 16. 0.625 mg 3 half lives passed (60 seconds x 3 = 180 seconds = 3 minutes), so 5/2 = 2.5, 2.5/2 = 1.25, 1.25/2 = 0.625 17. 6 years 3 half lives passed (4/2=2, 2/2=1, 1/2=0.5) each of which is 2 years, so a total of 6 years. 18. 75 minutes (1 hour and 15 minutes) 3 half lives passed (10/2 = 5, 5/2 = 2.5, 2.5/2 = 1.25), each of which is 25 minutes for a total of 75 minutes. 19. 31,250 atoms 5 half lives passed (0.90 seconds x 5 = 4.5 seconds) divide by 2 five times: 1,000,000/2 = 500,000; 500,000/2 = 250,000; 250,000/2 = 125,000; 125,000/2 = 62,500; 62,500/2 = 31,250 20. part 1: 0.0625 g (5 half lives, so divide by 2 five times); Part 2: you need to buy 102.4 g 10 half lives will pass before it gets to you, so multiply the amount you need for your experiment by 2 10 times (.1x2=.2, .2x2=.4, .4x2=.8, .8x2=1.6, 1.6x2=3.2, 3.2x2=6.4, 6.4x2=12.8, 12.8x2=25.6, 25.6x2=51.2, 51.2x2=102.4) 21. krypton – 92 22. zirconium – 97 23. rubidium – 96 24. there should be two neutrons 25. plutonium – 239

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