Warm-Up 10/28/13 Imagine winning a $1000 prize, but the conditions of the award require you to spend ½ of the amount that remains each month. How long will it take for ½ of the prize to be gone? After how many months would you be left with less than $1.00?

Stability & Half-Life Monday 10/28/13

Stability and the N/P Ratio From the graphing activity: If a nucleus is too far from a n/p ratio of 1, it is most likely going to be radioactive. Different types of decay are good at decreasing protons, neutrons, or electrons. The type depends on what particle there are too many of!

Measuring Decay The time it takes for ½ of all the radioactive nuclei in an object to decay is called the “Half-life.” The half-life for all radioisotopes is different—some types take fractions of a second, and some take millions of years for ½ of the nuclei to decay!

Counting Half-Lives Suppose you started with 100 radioactive nuclei. After 1 half-life, 50 would still be radioactive After 2, 25 are still radioactive After 3, ~12.5 are still radioactive After 4, ~6.25 are still radioactive. See the pattern?

Example Calculation Nitrogen 13 emits beta radiation and decays to carbon 13 with a half-life (t1/2) of 10 minutes. Assume you start with 2.0 grams of nitrogen 13. How long is three half-lives? How many grams of the isotope will still be present at the end of three half-lives?

Decay graphs “Decay curves” show the amount of radioactive nuclei remaining as time passes. All decay curves have a similar shape. We can use them to find the half-life of a radioisotope

Your Job Complete the practice half-life problems for tomorrow. On Tuesday, we will check the homework and then look at examples of how half-life is used in different types of sciences QUIZ Wednesday 10/30 TEST Monday 11/4