Radioactivity 11
- 2. Atoms Bond-fill outer valence shell Decay-Breakdown into energy and particles The ones that decay are usually unstable isotopes of an atom
- 3. Decay Types Alpha decay-releases alpha particles (Helium atoms, large) and stopped by paper or clothing. Beta decay-releases beta particles (electron, small) and stopped by aluminum. Gamma decay-releases gamma rays (no charge or mass) and stopped by thick concrete or strong lead.
- 4. Half-Life Amount of time it takes for half of a radioactive substance to decay Used to tell how old various rock samples and fossils are 0.1 s Ca-36 12.3 y H-3 10 m N-13 3.4 s O-21 138 d Po-210 4.5 BY U-238 Half-Life Isotope Half-Life Isotope
- 5. Half Life Example If 10 mg of iodine 131 is given to a patient, how much is left after 24 days? The half-life of iodine-131 is 8 days. 10 mg Mass 32 D 24 D 16 D 8 D 0 D Time
- 6. Answer After 24 Days you have 1.25 mg left and 3 half lives have past 0.625 mg 1.25 mg 2.5 mg 5 mg 10 mg Mass 32 D 24 D 16 D 8 D 0 D Time
- 7. Half Life Example Iodine-131 is used to destroy thyroid tissue in the treatment of an overactive thyroid. The half-life of iodine-131 is 8 days. If a hospital receives a shipment of 200 g of iodine-131, how much I-131 would remain after 32 days?
- 8. Answer After 32 days only 12.5 g of the sample remains, which means 4 half lives have past. 12.5 g 25 g 50 g 100 g 200 g Mass 32 D 24 D 16 D 8 D 0 D Time
- 9. Half-Life Example C-14 half life = 5730 years ¾ of the original C-14 of a fossil decayed. How many half lives have past? How old is this fossil? If you started with 250 grams of C-14, how much remain?
- 10. Answer ¾ decay of sample means 2 half lives, 25% remains, 75% decayed and therefore in this example 62.5 g remain 6.25% 12.5% 25% 50% 100% Original Mass Remaining % 15.625 g 31.25 g 62.5 g 125 g 250 g Original Mass Remaining (g) 4 3 2 1 0 Half Lives Past 22920 Y 17190 Y 11460 Y 5730 Y 0 Y Time