Radioactive Decay

Types of Radioactive Decay Alpha Decay: nucleus eject an alpha particle (made of 2 protons and 2 neutrons – a helium nucleus)

Types of Radioactive Decay Beta Decay: nucleus emits an electron or positron (electron with positive charge)

Types of Radioactive Decay Gamma Decay: nucleus emits highly energetic photons

Types of Radioactive Decay Alpha Decay can be shielded by a piece of paper Beta Decay can be shielded by aluminum foil Gamma Decay can be shielded by several centimeters of lead

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

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

Practice Problems 1.The half-life of radon-222 is 4.0 days. How much of a 100 g sample is left after 16.0 days? 2.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? 3.What is the half-life of a g sample of nitrogen-16 that decays to 12.5 g in 33 seconds? 4.How old is a bone if it presently contains 2.5 g of carbon-14, but was estimated to originally contain 80.0 g of carbon-14? The half-life of carbon-14 is 5,700 years g 0.5 g 11 s 28,500 years

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