Embedded Files
Get the formative assessment: FA30.1.docx
Get the reference for Isotopic Masses: IsotopicMass.pdf
Get more practice problems: Worksheet-ProblemsFrom30.1.docx
The formative assessment solved:
1 u = 1.6605x10-27 kg = 931.5 MeV, 10n = 1.008665 u
1. Find the missing particle or nucleus in these decays: (These are fictitious - ignore neutrinos for now)
Watch these videos to grade your FA:
2. What is the kinetic energy of the alpha particle that 208Po (m = 207.981222 u) gives off becoming 204Pb (m = 203.973020) in MeV?
(5.216 MeV)
3. Imagine it is possible for N-14 undergo both β- and β+ decay. Write the complete decay equation below for each (complete with neutrino or anti-neutrino)
Watch the video to grade your FA:
More examples:
4. You have 24.0 grams of a radioactive substance with a half life of 14.0 minutes. In what time will you have 3.00 grams of it left?
(42 min)
5.
The activity of a sample with a half-life of 23.5 minutes is initially 3.412x106 counts/second. What will it be in 6.00 hours?
(83.5 counts/sec)
If K-40(m = 39.964 u) had a half life of 14.0 hours, (It's actually stable) what would be the activity of 0.0240 grams of it?
(4.97x1015 counts/sec)
More Practice Problems: (Get this worksheet)
Problems from 30.1 - Radioactive Decay (Use your Isotope reference for this)
1. Find the missing particle or nucleus in these decays: (ignore neutrinos for this)
Solutions:
1a: <Video>
1b: <Video>
1c: <Video>
1d: <Video>
Alpha Decay - Find the energy released in MeV of these alpha decays:
2. 208Po (m = 207.981222 u) → 204Pb (m = 203.973020) + α (5.216 MeV) <Video>
3. 152Dy (m = 151.9247139 u) → 148Gd (m = 147.9181098) + α (3.728 MeV) <Video>
4. No-257 (m = 257.0968528 u) → Fm-253 (m = 253.0851763) + α (8.452 MeV) <Video>
5. Pa-226 (m = 226.0279327 u) → Ac-222 (m = 222.0178289) + α (6.987 MeV) <Video>
6. Am-234 (m = 234.0477940 u) → Np-230 (m = 230.0378126) + α (6.873 MeV) <Video>
Balanced Beta decays
7. Imagine it is possible for the following nuclei to undergo both β- and β+ decay. Write the complete decay equation for each:
7a: <Video>
7b: <Video>
7c: <Video>
7d: <Video>
Half Life and Decay Rates - Integer number of half life
8. A radioactive substance has a half life of 13.0 s. If you have an activity of 480. counts per second initially, what is the activity in 65.0 s? (15.0 counts/s) <Video>
9. A radioactive substance has a half life of 2.50 years. If you have 128. g initially, after what time do you have only 2.00 grams left? (15.0 years) <Video>
10. A radioactive substance starts off with 3240 atoms, and in 48.0 minutes, is down to 405 atoms. What is its half life? (16.0 minutes) <Video>
11. A radioactive substance has a half life of 47.0 s. If you have 1920 g initially, how much is left after 329 s? (15.0 grams) <Video>
12. A radioactive substance has a half life of 12.0 minutes. If you have an activity of 5.12x104 counts/sec initially, after what time do you have an activity of 1.28x104 counts/sec? (24.0 minutes) <Video>
13. A radioactive substance starts off with 3.20x1020 atoms, and in 85.0 minutes, is down to 1.00x1019 atoms. What is its half life? (17.0 minutes) <Video>
Half life and Decay Rates:
14. You have 45.0 grams initially of a sample with a half-life of 178 seconds. In what time will there be only 13.0 grams left? (319 s) <Video>
15. You have 78.0 grams of undecayed nuclei initially, and in 68.0 hours you have only 45.0 grams left. What is the half-life in hours? (85.7 hours) <Video>
16. A sample has a half-life of 13.7 seconds. If its activity is initially 196 counts per second, what will it be in 60.0 seconds? (9.42 counts/sec) <Video>
17. A sample has a half-life of 34.0 minutes. If after 87.0 minutes the activity is 137 counts per second, what was the activity initially? (807 counts/sec) <Video>
18. At first the activity of a radioactive sample is 278 counts per minute, and after 17.0 hours the activity is 171 counts per minute. What is the half-life of the sample in hours? (24.2 hours) <Video>
19. What is the activity of 13.0 g of Co-60 (m = 59.934 u) if it has a half life of 5.2708 years? (5.44x1014 counts/sec) <Video>
20. You have 0.150 g of S-35 (m = 34.969 u), and the activity is 2.37x1014 counts/s. What is the half life of S-35? (87.4 days) <Video>
21. A sample of P-32 (m = 31.974 u) has a half life of 14.262 days. How many grams do you have if it has has an activity of 4.20x1015 counts/sec? (0.397 g) <Video>
22. What is the activity of 1.20 μg of Sr-90 (m = 89.908 u) if it has a half life of 28.79 years? (6.13x106 counts/s) <Video>
23. If you have 0.0340 g of O-15 (m = 15.003) and the activity is 7.736x1018 counts/sec. What is its half life? (122 s) <Video>
24. A sample of C-11 (m = 11.0114 u) has a half life of 20.39 minutes. How many grams do you have if it has an activity of 3.10x1013 counts/sec? (1.00 μg) <Video>
The instruction for this unit:
Page updated
Report abuse