Nuclear Radiation Henri Becquerel Marie Curie Radioactivity Nuclear

Nuclear Radiation Henri′ Becquerel Marie Curie ? ? ? Radioactivity (Nuclear Decay) Ø spontaneous emission of high-energy radiation or charged particles from the nucleus of an atom

3 Types of Nuclear Radiation Alpha ( ) Beta ( –) Gamma ( ) + 2 p+2 n e–

3 Types of Nuclear Radiation ØPenetrating: Least to Most (damaging) – or

3 Types of Nuclear Radiation • Alpha Particle ( ) Øhelium nucleus Stopped Symbol Charge Mass by +2 4 – 1 0 • Gamma Ray ( ) 0 Øhigh-energy light (fastest) 0 • Beta Particle ( –) Øelectron (smaller, faster) paper aluminum 3 feet of Concrete or Lead

Nuclear Decay Rates

Half-life (t 1/2): • time at which half of initial amount remains.

Problem #1: The half-life of Zn-71 is 2. 4 minutes. If one had 100. 0 g at the beginning, how many grams would be left after 7. 2 minutes has elapsed? Solution: 7. 2 min ÷ 2. 4 min per half-life = 3 half-lives 100. 0 g ÷ 2 = 50. 0 g ÷ 2 = 25. 0 g ÷ 2 = 12. 5 g remain after 3 half-lives.

Problem #2: Os-182 has a half-life of 21. 5 hours. How many grams of a 10. 0 gram sample would have decayed after exactly two half-lives? Solution: 10. 0 g ÷ 2 = 5. 00 g ÷ 2 = 2. 50 g remain after 2 half-lives. (21. 5 hr length of half-life was irrelevant)

Problem #3: After 24 days, 2. 00 mg of an original 32. 00 mg sample is left. What is the half-life of the substance? Solution: 32. 00 mg ÷ 2 = 16. 00 mg ÷ 2 = 8. 00 mg ÷ 2 = 4. 00 mg ÷ 2 = 2. 00 mg remain after 4 half-lives.

Problem #4: A bone contains radioactive carbon-14 with a half-life of 5, 000 yrs. The bone is thought to have had 20. 0 mg of 14 C when the animal died and it now has 2. 5 mg of 14 C left. How old is the bone? Solution: 20. 0 mg ÷ 2 = 10. 0 mg ÷ 2 = 5. 0 mg ÷ 2 = 2. 5 mg after 3 half-lives. (3 half-lives) x (5, 000 yrs/half-life) = 15, 000 yrs

Quick Quiz! 1. Certain elements are radioactive because their atoms have A. B. C. D. more neutrons than electrons. an unstable nucleus. a small nucleus. more neutrons than protons.

Quick Quiz. 2. Which property does NOT describe an alpha particle? A. B. C. D. +2 charge a relatively large mass a negative charge low penetrating power

Quick Quiz. 3. When a radioactive nucleus releases a high-speed electron, the process can be described as A. B. C. D. oxidation. alpha emission. beta emission. gamma radiation.

Quick Quiz. 4. Which of the following is the symbol of a beta particle? A. B. C. D.