Chapter 7 - Radioactivity

1. Chapter 7 - Radioactivity Science 10

2. 7.1 Atomic Theory and Radioactive Decay • Radioactivity is the release of high energy particles or waves being emitted (released) from the decay (breakdown) of an unstable nucleus of an atom • Natural background radiation exists all around us.

3. Radiation • High-energy rays/particles emitted by radioactive sources. • Radioactive materials are in many things: • X-rays, radiation therapy and electricity generation are beneficial. • High energy particles and waves can do damage to DNA in our cells. When atoms lose high energy particles and waves, ions or even new atoms can be formed.

4. The Electromagnetic Spectrum All of the radiation found around in our environment is called natural background radiation

5. History: Roentgen • Roentgen named X-rays with an “X” 100 years ago because they were previously unknown.

6. Becquerel • Becquerel realized uranium emitted seemingly invisible energy.

7. Marie Curie and her husband Pierre named the energy radioactivity. Radium salts, after being placed on a photographic plate, leave behind the dark traces of radiation.

8. Geiger-Muller Counter Early discoveries of radiation relied on photographic equipment Later, more sophisticated devices such as the Geiger-Müller counter were developed to more precisely measure radioactivity.

9. Marie Curie • Discovereries and contributions to the field of radioactivity • https://www.youtube.com/watch?v=ZEV4KJBJvEg • https://www.youtube.com/watch?v=r4jCTiGSuwU

10. Isotopes • are different atoms of the same element, with a different number of neutrons in the nucleus. • Changing the # of neutrons changes the mass number • Remember: mass # = # protons + # neutrons • isotopes still have the same: • number of protons / atomic number • element symbol

11. Isotopes

12. Isotopes • Isotopes have different neutron numbers.

13. Atomic number stays the same as proton number doesn’t change. • Neutron number changes = different atomic mass.

14. Atomic Mass (the decimal #’s) • Atomic mass = average of the mass numbers for all isotopes of an element. • If 19.9% of boron atoms have 5 neutrons, 80.1% have 6 neutrons • 19.9% have a mass number of 10, and 80.1% have a mass number of 11 • (.199 * 10) + (.801*11) = 10.8 • atomic mass of boron = 10.8

16. Representing Isotopes • Isotopes are written using standard atomic notation (nuclear symbol). • Chemical symbol + atomic number + mass number. • Potassium has three isotopes,

17. Write the standard atomic symbol for the following: • Potassium-39 • Potassium-40 • Potassium-41

18. Write the standard atomic symbol for the following: • Potassium-39 • Potassium-40 • Potassium-41

19. Potassium is found in nature in a certain ratio of isotopes • 93.2% is potassium-39 • 1.0% is potassium-40 • 6.7% is potassium-41 • Atomic mass = (.932 x 39) + (.001 x 40) + (.067 x 41) = 39.1

20. Practice • Reading Check p291 • Practice Problems p291 • Worksheet

21. Radioactive Decay Radioactivity results from having an unstable nucleus. When these nuclei lose energy and break apart, decay occurs. • Radioactive decay is the process by which unstable nuclei lose energy by emitting radiation until they are stable. • They release energy until they become stable, often different atoms. • An element may have only certain isotopes that are radioactive. These are called radioisotopes.

22. Radioactive Decay How does the radioisotope Uranium-238 decay?

23. Radioactive Decay How does the radioisotope Uranium-238 decay? Change Mass #, And Atomic #

24. Three Types of Radiation • Ernest Rutherford (1871-1937)identified three types of radiation using an electric field. See page 294 (c) McGraw Hill Ryerson 2007

25. Positive alpha particles were attracted to the negative plate. • Negative beta particles were attracted to the positive plate. • Neutral gamma rays did not move towards any plate.

26. Alpha Radiation • Alpha radiation is a stream of alpha particles. • What are some characteristics of Alpha particles? See page 294 - 295 (c) McGraw Hill Ryerson 2007 Radium-226 releases an alpha particle and becomes Radon-222. Radon has two less protons than radium.

27. Alpha Radiation • Alpha radiation is a stream of alpha particles. • They are positively charged, and are the most massive of the radiation types. • Alpha particles are essentially the same as helium atoms. • Alpha particles are represented by the symbols . • Because it has two protons, it has a charge of 2+. • The release of alpha particles is called alpha decay. • Alpha particles are slow and penetrate materials much less than the other forms of radiation. A sheet of paper will stop an alpha particle. See page 294 - 295 (c) McGraw Hill Ryerson 2007 Radium-226 releases an alpha particle and becomes Radon-222. Radon has two less protons than radium.

28. Alpha Radiation is a stream of alpha particles • positively charged, and are the most massive of the radiation types. • essentially the same as helium atoms. • represented by the symbols . • Because it has two protons, it has a charge of 2+. • The release of alpha particles is called alpha decay. • slow and penetrate materials much less than the other forms of radiation. A sheet of paper will stop an alpha particle. See page 294 - 295 (c) McGraw Hill Ryerson 2007

29. Alpha Radiation Radium-226 releases an alpha particle and becomes Radon-222. Radon has two less protons than radium.

30. Practice • Practice Problems p295

31. Beta Radiation • What are some characteristics of Beta Particles?

32. Beta Radiation • A beta particle is an electron and is negatively charged. • represented by: Electrons are very tiny, so beta particles are assigned a mass of 0. Since there is only an electron, a beta particle has a charge of 1–.

33. Beta Radiation • Beta decay occurs when a neutron changes into a proton and an electron. • The proton stays in the nucleus, and the electron is released. • It takes a thin sheet of aluminum foil to stop a beta particle. Iodine-131 releases a beta particle and becomes xenon-131. A neutron has turned into a proton and the released electron. See page 296 (c) McGraw Hill Ryerson 2007

34. Practice • Do practice problems p296

35. Gamma Radiation What are some characteristics of Gamma particles?

36. Gamma Radiation • Gamma radiation is a ray of high-energy, short-wavelength radiation. • Gamma radiation has no charge and no mass, and is represented by: • Has no charge • highest-energy form of electromagnetic radiation. • It takes thick blocks of lead or concrete to stop gamma rays. See page 297 (c) McGraw Hill Ryerson 2007

37. Is the gamma Decay reaction balanced?

38. Radiation Summary • Nuclear equations are written like chemical equations, but represent changes in the nucleus of atoms. • Chemical equations represent changes in the position of atoms, not changes to the atoms themselves. • The sum of the mass numbers does not change. 2. The sum of the charges in the nucleus does not change. See pages 298 - 299 (c) McGraw Hill Ryerson 2007 Take the Section 7.1 Quiz

39. Radioactivity Decay Summary

40. Check your progress • How is mass number of an element determined? • How do you represent a larger nucleus such as radium-226? • Why does an alpha particle have a positive charge? • How does beta decay result in the production of an element with one more protons than the nucleus started out with? • Since gamma rays are not made of matter, how can they be detected?

41. Reading Check • Page 297