FA30.1 - Radioactivity

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           

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:

5:42Isotopes and Atomic Notation

Atomic Notation Example 1

Atomic Notation Example 2

Atomic Notation Example 3

Atomic Notation Example 4

Atomic Notation Example 5

10:03Radioactivity

Radioactivity Example 1

Radioactivity Example 2

Radioactivity Example 3

Radioactivity Example 4

5:40Decay Series

6:05Alpha Decay

Alpha Decay Example 1

Alpha Decay Example 2

4:13Quantum Tunneling

7:57Beta Decay

6:08Gamma Decay

Gamma Decay Example 1

Gamma Decay Example 2

7:49Activity

Activity Example 1

Activity Example 2

11:18Exponential Decay

Exponential Decay Example 1

Exponential Decay Example 2

Exponential Decay Example 3

Exponential Decay Example 4

Exponential Decay Example 5

Exponential Decay Example 6

6:37Radiometric Dating