Radioactive Decay

1. Radioactive Decay

2. Types of Radioactive Decay • Alpha Decay: nucleus eject an alpha particle (made of 2 protons and 2 neutrons – a helium nucleus) • Can be shielded by a piece of paper • Beta Decay: nucleus emits an electron or positron (electron with positive charge) • Can be shielded by aluminum foil • Gamma Decay: nucleus emits highly energetic photons • Can be shielded by several centimeters of lead

3. Half-Life • The half-life of a radioisotope is the time required for one half of the atoms in a sample to degrade into a more stable material • The half-life for a given isotope is always the same • Half-lives vary from isotope to isotope, ranging from fractions of a second to millions of years

5. Half-Lives • Ex: The half-life of Strogenium is 2 seconds. How much of a 10 g sample will be left after 6 seconds? 6 seconds x = 3 half-lives • After 0 half-lives, 10 g are left. • After 1 half-life, 5 g are left. • After 2 half-lives, 2.5 g are left. • After 3 half-lives, 1.25 g are left. 1 half-life 2 seconds

6. Practice Problems • The half-life of radon-222 is 4.0 days. How much of a 100 g sample is left after 16.0 days? • Cesium-137 has a half-life of 30 years. If 4.0 g of cesium-137 disintegrates over a period of 90 years, how many grams would remain? • What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g in 33 seconds? • How old is a bone if it presently contains 5.0 g of carbon-14, but was estimated to originally contain 80.0 g of carbon-14? The half-life of carbon-14 is 5,730 years. 6.25 g 0.5 g 11 s 22,920 years

7. Practice Problem Pd-100 has a half-life of 3.6 days. If there are 6.02 x 1023 atoms at the start, how many atoms would be present after 20.0 days?