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- 1. Unit 5: The Atom Chapter 19: Radioactivity
- 2. 19.1 Alpha, Beta, and Gamma Radiation <ul><li>Radioactivity – The process by which certain elements emit particular forms of radiation. </li></ul><ul><li>Three Forms: Alpha, Beta, and Gamma </li></ul><ul><li>Alpha Particles – Fast-flying, positively charged subatomic particles make up radiation. </li></ul><ul><li>Alpha Particle – Made of two protons and two neutrons. (Nucleus of a helium atom. </li></ul>
- 3. 19.1 Alpha, Beta, and Gamma Radiation <ul><li>Beta Particles – Fast-flying, negatively charged subatomic particles that make up beta radiation. </li></ul><ul><li>Beta Particle – An electron that is ejected by an atomic nucleus. </li></ul>
- 4. 19.1 Alpha, Beta, and Gamma Radiation <ul><li>Gamma Radiation – An extremely energetic form of electromagnetic radiation. Has more energy than visible light. Carries no electric charge and has no mass. </li></ul>
- 5. 19.2 Radioactivity Is a Natural Phenomenon <ul><li>Radioactivity has been around forever. </li></ul><ul><li>Cells can repair most kinds of molecular damage caused by radiation. </li></ul><ul><li>Mutation – When radiation alters the genetic information of a cell by damaging its DNA molecules. (Can lead to cancer) </li></ul><ul><li>Radon-222 – An inert gas arising from uranium deposits. </li></ul><ul><li>EPA suggest that anywhere from 7,000 to 30,000 cases of lung cancer each year are attributed to radon exposure. </li></ul>
- 6. 19.2 Radioactivity Is a Natural Phenomenon <ul><li>1/5 of our annual exposure to radiation comes from non-natural sources. </li></ul><ul><li>Nuclear power industries generate about 10,000 tons of radioactive waste a year that is contained ! </li></ul>
- 7. 19.2 Radioactivity Is a Natural Phenomenon <ul><li>Origins of radiation exposure for average American: </li></ul><ul><li>81% Natural background </li></ul><ul><li>15% Medicine and diagnostics </li></ul><ul><li>4% Consumer products </li></ul>
- 8. 19.3 Radioactivity Results from an Imbalance of Forces in the Nucleus <ul><li>Electrical charges with the same sign repel one another. </li></ul><ul><li>Strong nuclear force – Acts between nucleons, is very strong, but acts only over small distances </li></ul><ul><li>Repulsive electrical interactions are long-ranged. </li></ul><ul><li>Large nucleus are not as stable as small ones. </li></ul><ul><li>Radioactive decay - Large, unstable nucleus breaks down releasing gamma radiation. </li></ul>
- 9. 19.3 Radioactivity Results from an Imbalance of Forces in the Nucleus <ul><li>Neutrons act as a “nuclear cement” that hold the atomic nucleus together. </li></ul><ul><li>A neutron has two drawbacks: </li></ul><ul><li>1. Neutrons are not stable when they are by themselves. (It decays to a proton by emitting an electron and sheds alpha particles.) </li></ul><ul><li>2. Neutrons are not stable when protons are attracted by strong protons in the nucleus. (Elements with more than 83 protons are radioactive.) </li></ul>
- 10. 19.4 A Radioactive Element Can Transmute to a Different Element <ul><li>Transmutation - The changing of one element to another. </li></ul><ul><li>Occurs when a radioactive nucleus emits an alpha or beta particle and the atomic number and identity of the element change. </li></ul><ul><li>When transmutation occurs, energy is released. </li></ul><ul><li>When an element ejects an alpha particle from it nucleus, the mass number of the atom is decreased by 4 and its atomic number is decreased by 2. (Falls back 2) </li></ul>
- 11. 19.4 A Radioactive Element Can Transmute to a Different Element <ul><li>When an beta particle is ejected the mass of the atom is not changed, but its atomic number increases by 1.(Steps up one) </li></ul>
- 12. 19.5 The Shorter the Half-life, the Greater the Radioactivity <ul><li>Radioactive materials by their very nature, decay via various methods to form other elements, ultimately to form stable non-radioactive isotopes. </li></ul><ul><li>The radioactive decay is measured in a characteristic of time called Half-life. </li></ul><ul><li>The half-life is the time needed for half of the radioactive atoms to decay. </li></ul>
- 13. 19.5 The Shorter the Half-life, the Greater the Radioactivity <ul><li>After 20 half-lives, the initial quantity is diminished to one-millionth of the original. </li></ul><ul><li>Remarkably constant and not affected by external conditions. </li></ul><ul><li>Measured by a Geiger counter. </li></ul>
- 14. Geiger Counter <ul><li>If you monitor a radioactive substance with a Geiger counter, you will hear "clicks" every time the device detects a particle of radiation. Over time, if you graphed the number of clicks per second you would see a graph resembling something like you see below: </li></ul>
- 15. Geiger Counter
- 16. Geiger Counter <ul><li>Depending on how quickly an element decays, the time needed to make the above graph could take anywhere from a fraction of a second to billions of years. </li></ul><ul><li>One way to describe how fast a radioactive substance decays is to determine how long it will take half of the currently present atoms to decay. Let's look at a particular example - Iodine-131 which is used to diagnose problems with the thyroid gland. </li></ul>
- 17. Geiger Counter
- 18. Geiger Counter <ul><li>By looking at the graph you can see that half of the Iodine-131 has decayed every 8 days. We then say that Iodine-131 has a "half-life" of 8 days. </li></ul>
- 19. 19.6 Isotopic Dating Measures the Age of Material <ul><li>All plants and animals contain a tiny quantity of radioactive carbon-14. </li></ul><ul><li>Carbon-14 emits a beta particle, and decays back to nitrogen. </li></ul><ul><li>The longer a plant or animal is dead the less carbon-14 it contains. </li></ul><ul><li>The half-life of carbon-14 is about 5,730 years. </li></ul>
- 20. 19.6 Isotopic Dating Measures the Age of Material <ul><li>Carbon-14 dating – The way scientists calculate the age of artifacts. </li></ul><ul><li>Carbon-14 dating is only useful to 50,000 years into the past. Then they guess! </li></ul><ul><li>Fluctuations in the sun’s magnetic field, Earth’s climate, and water temperature means that carbon-14 has fluctuated throwing off this dating method. </li></ul>

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