Nuclear Radiation ??? Radioactivity (Nuclear Decay) Henri′ Becquerel Marie Curie ??? 1896 Becquerel accidentally develops photo plate with U salts w/o sunlight Curie exp. and named it radioactivity. Both won Nobel Prize in Physics, she won for Chem later. Died 1934 leukemia. Radioactivity (Nuclear Decay) spontaneous emission of high-energy radiation or charged particles from the nucleus of an atom

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

3 Types of Nuclear Radiation Penetrating: Least to Most (damaging)  –  Video clip is “Radioactivity” from Safari playlist (4 min) or Concrete

3 Types of Nuclear Radiation Stopped by Symbol Charge Mass Alpha Particle () helium nucleus +2 4 paper Beta Particle (–) electron (smaller, faster) aluminum –1 Gamma Ray () high-energy light (fastest) 3 feet of Concrete or Lead

Nuclear Decay Rates Demo – penny ½ life

Half-life (t1/2): time at which half of initial amount remains. 6 Ask several questions about calculations. 6

Problem #1: The half-life of Zn-71 is 2. 4 minutes. If one had 100 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 50.0 g ÷ 2 = 25.0 g 25.0 g ÷ 2 = 12.5 g remain after 3 half-lives.

Problem #2: Os-182 has a half-life of 21. 5 hours 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 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 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 16.00 mg ÷ 2 = 8.00 mg 8.00 mg ÷ 2 = 4.00 mg 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 14C when the animal died and it now has 2.5 mg of 14C left. How old is the bone? Solution: 20.0 mg ÷ 2 = 10.0 mg 10.0 mg ÷ 2 = 5.0 mg 5.0 mg ÷ 2 = 2.5 mg after 3 half-lives. (3 half-lives) x (5,000 yrs/half-life) = 15,000 yrs

Certain elements are radioactive because their atoms have Quick Quiz! Certain elements are radioactive because their atoms have more neutrons than electrons. an unstable nucleus. a small nucleus. more neutrons than protons. 11

Which property does NOT describe an alpha particle? Quick Quiz. Which property does NOT describe an alpha particle? +2 charge a relatively large mass a negative charge low penetrating power 12

Quick Quiz. When a radioactive nucleus releases a high-speed electron, the process can be described as oxidation. alpha emission. beta emission. gamma radiation. 13

 Quick Quiz. Which of the following is the symbol of a beta particle? 14