2. Wednesday, November 4 th, 2015

3. The blue grid below represents a quantity of C 14. Each time you click, one half-life goes by and turns red. C 14 – blue N 14 - red As we begin notice that no time has gone by and that 100% of the material is C 14 Half lives % C 14 %N 14 Ratio of C 14 to N 14 0100%0%no ratio 2

4. The grid below represents a quantity of C 14. Each time you click, one half-life goes by and you see red. C 14 – blue N 14 - red Half lives % C 14 %N 14 Ratio of C 14 to N 14 0100%0%no ratio 150% 1:1 After 1 half-life (5730 years), 50% of the C 14 has decayed into N 14. The ratio of C 14 to N 14 is 1:1. There are equal amounts of the 2 elements. 3

5. The blue grid below represents a quantity of C 14. Each time you click, one half-life goes by and you see red. C 14 – blue N 14 - red Half lives % C 14 %N 14 Ratio of C 14 to N 14 0100%0%no ratio 150% 1:1 225%75%1:3 Now 2 half-lives have gone by for a total of 11,460 years. Half of the C 14 that was present at the end of half-life #1 has now decayed to N 14. Notice the C:N ratio. It will be useful later. 4

6. The blue grid below represents a quantity of C 14. Each time you click, one half-life goes by and you see red. C 14 – blue N 14 - red Half lives % C 14 %N 14 Ratio of C 14 to N 14 0100%0%no ratio 150% 1:1 225%75%1:3 312.5%87.5%1:7 After 3 half-lives (17,190 years) only 12.5% of the original C 14 remains. For each half-life period half of the material present decays. And again, notice the ratio, 1:7 5

7. 6

8. What is the half life represented in this graph? 7

9. Nuclear Half-life Every statistically large group of radioactive nuclei decays at a predictable rate. This is called the half-life of the nuclide Half life is the time it takes for half (50%) of the Radioactive nuclei to decay to the daughter Nuclide

10. Beanium decay 64 beans 32 beans 16 beans 8 beans 4 beans Successive half cycles 1 2 3 4 50% What does the graph of radioactive decay look like? This is an EXPONENTIAL DECAY CURVE

11. Loss of mass due to Decay Amount64321684 Fraction left1½¼1/8 1/16 Half life’s1234 If each half life took 2 minutes then 4 half lives would take 8 min. The equation for the No. of half lives is equal to: T (elapsed – total) / T (one half Life) 32 minutes / 4 minutes = 8 half life’s

12. In order to solve these half problems a table like the one below is useful. For instance, If we have 40 grams of an original sample of Ra-226 how much is left after 8100 years? ½ life period% original remaining Time Elapsed Amount left 01000 40 grams 1501620 yrs 20 grams 2253240 ? 312.54860 ? 46.256480 ? 53.1258100 ? 10 grams 5 grams 2.5 grams 1.25 grams

13. Problem 1: A sample of Iodine-131 had an original mass of 16g. How much will remain in 24 days if the half life is 8 days? Step 1: How many half lives? Half life= T (elapsed) / T half life = 24/8 = 3 Step 2: 16g (starting amount)  8  4  2g

14. Problem 2: What is the original amount of a sample of H–3 if after 36.8 years 2.0g are left if the half life of H-3 is 12.26 years? 36.8 yrs / 12.26 yrs = 3 half lives. ___  ___  ___  2 g Work backwards! Half life32 grams Half life 24 grams Half life 18 grams Time zero16 grams

15. Problem 3: How many half life periods have passed if a sample has decayed to 1/16 of its original amount? Time zero1x original amount First half life½ original amount Second half life¼ original amount Third half life1/8 Fourth half life 1/16

16. Problem 4: What is the ½ life of a sample if after 40 years 25 grams of an original 400 gram sample is left ? Step 1: 400  200  100  50  25 4 half lives Step 2: Elapsed time = # HL 40 years = 4 HL Half-life Half life = 10 years

17. For each problem you need to identify 1. Number of half-lives 2. Starting amount (%, fraction, g, etc.) 3. Ending amount 4. Length of one half-life 5. Total amount of time to get from starting amount to ending amount

18. Wednesday, November 4 th, 2015

19. What are the particles? Alpha Beta Gamma Positron

20. Examples – What goes where?! Sodium-23 undergoes beta decay Carbon-14 undergoes electron capture. A radioactive isotope goes through alpha decay to produce Nitrogen-14. Magnesium-24 is produced from the positron emission of an unstable isotope. The beta decay of Uranium-235 produces a gamma particle as well.

21. Sodium-23 undergoes beta decay

22. Carbon-14 undergoes electron capture.

23. A radioactive isotope goes through alpha decay to produce Nitrogen-14.

24. Magnesium-24 is produced from the positron emission of an unstable isotope.

25. The beta decay of Uranium-235 produces a gamma particle as well.

26. For each problem you need to identify 1. The reactant(s) 2. The product(s) 3. Total mass on the left of the arrow 4. Total mass on the right of the arrow 5. Total atomic number on the left of the arrow 6. Total atomic number on the right of the arrow