1. 1 I.What is radioactivity? A.Nuclear radiation – charged particles or energy emitted by an unstable nucleus. 1.Radioactivity – unstable nucleus emits one or more particles or energy in the form of electromagnetic pulse. 2.4 types of radiation: a)Alpha particle: α 1)Has +2 charge. 2)Consists of 2 protons and 2 neutrons. 3)Resembles a helium nuclei. 4 2 He (top # = mass #, bottom # = atomic #) 4)Does not travel far through matter b/c it is so massive.

2. 2 b)Beta particle: β 1)Has –1 charge. 2)Fast moving electrons. 3)Symbol: 0 -1 e 4)Travel farther and faster through matter b/c not as massive as α. 5)Most stopped by 3 mm of Aluminum or 10 mm or wood. c)Gamma particle: γ 1)Not matter and has no charge => electromagnetic energy. 2)High energy radiation. 3)Penetrates up to 60 cm of Al or 7 cm of lead.

3. 3 d)Neutron emission: 1)Has no charge. 2)Symbol: 10n. 3)Can travel farther than α or β particles. 4)Need 15 cm thick block of lead to stop neutrons. 5)Very dangerous to organisms. B.Nuclear decay: 1.Alpha decay: a)An alpha particle is released from an atom. b) 226 88 Ra -> 222 86 Rn + 4 2 He c)226 = 222 + 4 88 = 86 + 2

4. 4 2.Beta decay: a)A nucleus gains a proton and loses a neutron. b) 14 6 C -> 14 7 N + 0 -1 e c)14 = 14 + 0 6 = 7 + -1 d)Mass number does not change. C.Radioactive Decay Rates 1.Half-life – time required for half a sample of radioactive nuclei to decay. a)Varies with each radioactive isotope.

5. 5 2.Problems: 1.Radium-226 has ½-life = 1599 years  How long did it take for 7/8 to disappear? 1)How much is remaining? 1 – 7/8 = 1/8 remaining 2)How many ½-lives did it take? ½ x ½ x ½ = 1/8, so 3 ½-lives 3)Total time: 3 ½-lives x 1599 yrs. = 4797 yrs 1 ½-life Practice p. 228 (1-5)

6. 6 II.Nuclear Fission and Fusion A.Nuclear Fission – nucleus SPLITS into two or more smaller fragments, releasing neutrons and energy. 1.Release of energy is expressed as: E = mc 2 E = energy (Einstein)m = mass c = speed of light 2.Nuclear chain reaction – series of fission reactions in which the neutrons emitted by a dividing nucleus cause the division of other nuclei. (Figure 7-8) a)Critical mass – minimum mass needed to sustain a chain reaction.

7. 7 B.Fusion – light nuclei combine at high temperatures, forming heavier nuclei and releasing energy. 1.Occurs in stars. 2.4 H -> 4 2 He + γ (gamma ray) III.Dangers and Benefits of Nuclear Radiation A.Dangers: 1.Health concerns: a)Change hemoglobin b)Lung cancer (radon in buildings) c)Radiation sickness (cancer, sterility, hair loss, etc.) d)Genetic mutations

8. 8 B.Benefits: 1.Used to treat cancers (brain, etc.) 2.Radioactive tracer 3.Nuclear power: a)Advantages: 1)No gaseous pollutants 2)More known energy reserves than fossil fuels. b)Disadvantages: 1)Radioactive products => nuclear waste 2)Public safety => nuclear meltdown (Chernobyl and Three-mile island). 3)Very expensive