Unit 5 Physical Science Radioactivity Answer Key

Transcription

1 Unit 5 Physical Science Radioactivity Answer Key Page True 2. False: The higher the frequency is, the higher the energy is. 3. True 4. False: Energy increases as frequency increases. 5. False: The shorter the wavelength is, the greater the energy. Page True 2. True 3. False: Ultraviolet light has a shorter wavelength than visible light. 4. False: Infrared radiation has a lower frequency than visible light. 5. False: AM radio waves have less energy than FM radio waves. Page 200 Study Prep Answers will vary, but look for evidence that demonstrates an understanding of the relationship between frequency and wavelength for the different forms of electromagnetic radiation. Students should also identify how the wavelength and frequency changes for each form of radiation. Encourage students to start their concept map with the term electromagnetic radiation. For students having difficulty placing the terms in the concept map encourage them to use diagrams instead. Page Review Questions 1. a) Wavelength is the distance from one point on one wave to the same point on the next wave. b) Frequency is the number of waves that pass a certain point in a given amount of time. c) Electromagnetic radiation is radiant energy that travels at the speed of light ( km/s). d) The electromagnetic spectrum is the entire range of wavelengths or frequencies of electromagnetic radiation from the longest radio waves to gamma rays. It includes visible light. 2. The wavelength of electromagnetic radiation decreases as the frequency of the radiation increases. Unit 5 Answer Key 1 Science Foundations 10

2 3. The unit for frequency is the hertz (Hz). 4. The energy carried by a wave increases as the wavelength decreases. 5. a) AM radio has a longer wavelength than FM radio. b) TV broadcast signals have a longer wavelength than microwave radiation. c) Blue light has a longer wavelength than X-rays. 6. a) Ultraviolet light has higher energy than infrared light. b) Shortwave radio has higher energy than aircraft radio waves. c) Gamma rays have higher energy than green light. 7. Radio waves are generally associated with: a) low-frequency waves b) low-energy waves c) invisible radiation 8. The inverse relationship between wavelength and energy means that when the wavelength is long, the energy carried by the wave is low. When the wavelength is short, the energy carried by the wave is high. 9. All electromagnetic radiation is radiant energy and consists of different forms of the same type of energy. In this sense, all forms of electromagnetic energy could be considered a type of light. Page True 2. False: Not all electrons are beta particles. (Electrons that occupy energy levels surrounding the nucleus of an atom are not considered to be beta particles.) 3. True 4. False: A beta particle has a charge of True Page Pages Review Questions 1. a) Radioactive decay is a process where particles and energy are released from the nucleus of an atom. b) Atomic number is the number of protons in the nucleus of an atom. c) Mass number is the number of particles in the nucleus. That is, it is the sum of the number of protons and the number of neutrons. Unit 5 Answer Key 2 Science Foundations 10

3 d) Isotopes are atoms of the same element (same atomic number) that differ in the number of neutrons they possess. e) Decay products are the particles or energy produced when an atom undergoes nuclear decay. Common products are alpha and beta particles and gamma rays. f) A half-life is the length of time that it takes for half of a radioactive sample to decay. 2. Three common decay products are alpha particles, beta particles, and gamma rays. 3. Alpha particles are composed of protons and neutrons. 4. A beta particle is composed of a fast-moving electron. 5. Gamma radiation is part of the electromagnetic spectrum, which may be thought of as waves of pure energy. (Note: The particle theory of radiation, in which gamma radiation is thought of as being composed of high energy photons, is beyond the course of studies. Even so, showing gamma radiation in the equations in this section does imply that it also has particle-like characteristics.) 6. a) alpha and beta b) gamma c) alpha d) beta e) gamma f) gamma g) beta and gamma h) alpha i) alpha j) beta 7. a) alpha b) gamma c) beta d) beta e) alpha f) beta g) gamma h) gamma i) alpha j) beta 8. a) The graph (on page 206) shows carbon-14 with a half-life of about 6000 years. (A more precise estimate than that shown on the graph is 5730 years.) b) 50% remains after one half-life. c) 12.5% of a sample remains after three half-lives. 9. After two half-lives, 108 g of carbon-14 remains from a 432-g sample. 10. The mass that remains is 500 g. (Since years corresponds to approximately two half-lives, the 2000-g sample will decay first to 1000 g and then finally to 500 g.) 11. After years, the sample has 6.25% remaining from the original amount. A year-old sample has gone through four half-lives, dropping the percentage to 50%, then 25%, then 12.5%, and finally to 6.25%. Unit 5 Answer Key 3 Science Foundations 10

4 12. a) Uranium-238 has a half-life of 4.5 billion years (4.5 x 10 9 years). b) Potassium-40 has a half-life of 1.3 billion years (1.3 x 10 9 years). 13. Uranium-238 decays into lead-206. The rock will therefore contain both lead and uranium. Assume that all the lead-206 came from the decomposition of the uranium. By comparing the amount of each of these elements, you could determine how much uranium was present when the rock first formed. 14. Argon-40 is produced when potassium-40 decays. 15. Carbon dating will not work in this application except to verify that the bone is more than about years old. Beyond this time frame, not enough carbon-14 is left in the sample to get a good measurement. 16. Uranium-238 and potassium-40 dating methods are suitable for measuring a sample that is about 2 million years old, provided these isotopes are present in the rock. 17. To measure rocks that are 4 billion years old, uranium-235 is used. Page Review Questions 1. a) fission b) fusion c) fusion d) fission e) fission f) fusion g) fission 2. a) c b) d c) g 3. a) An iron atom carrying excess energy decomposes into an iron atom and a gamma ray. b) Lithium and hydrogen fuse to release two alpha particles. c) Actinium decays to francium and an alpha particle. d) An electron strikes a beryllium nucleus resulting in the formation of lithium. 4. The nuclear reactors control the amount of heavy water, which in turn controls the rate of the fission reaction. 5. Fusion nuclear reactions are common in stars like our Sun. Page Review Questions 1. Answers may vary. They could include the following: a) microwave ovens, smoke detectors b) X-rays, CAT scans, cancer therapy, nuclear medicine c) structural flaw detection, detection of metals in concrete (e.g., rebar) d) carbon dating, astronomy 2. Microwaves cause water and fat molecules to vibrate more rapidly. Unit 5 Answer Key 4 Science Foundations 10

5 3. Americium emits alpha particles, which allows electric current to flow in a smoke detector. The smoke interrupts the current, which triggers the alarm. 4. a) Radon gas in the Earth s crust b) Alpha decay in uranium 5. Ionizing radiation is radiation with enough energy to remove electrons from atoms to form ions. It can damage living cells. 6. Alpha particles, beta particles, gamma rays, and X-rays 7. Answers may vary. They could include: medical X-rays, nuclear medicine, and consumer products. 8. Somatic damage is damage to any part of the body except the reproductive organs, and can lead to cancer. Genetic damage is damage to reproductive cells. 9. CAT scans pass X-rays through the body. Detectors are located in loops around the body. As the X-ray source moves around the body, it generates a three-dimensional image. 10. Answers may vary. For example: a) Potential benefit: X-rays identify tooth decay before it becomes visible in a dental exam. Being able to treat this condition early means less medical intervention will be needed later. Potential harm: X-rays are a source of ionizing radiation. Danger increases with dosage. Lead shields reduce exposure to X-rays. Normally, a few X-rays a year is not considered too great a risk, given the potential benefits. b) Potential benefit: Nuclear power does not produce greenhouse gases or reduce water flows in fish habitat. The price of energy from nuclear power can be competitive with other sources. Potential harm: Some reactors that use enriched uranium, such as in the United States and Russia, have the potential to have a catastrophic failure. Both countries have had such disasters (Three Mile Island and Chernobyl). Radioactive waste material lasts for hundreds of thousands of years. It would be extremely difficult if not impossible to ensure safe storage for such a long period of time. c) Potential benefit: Radioactive iodine has the potential to kill cancer cells. Potential harm: Because it kills all fast-growing cells, it has many side effects, such as temporarily knocking out the immune system. This opens up the chance of life-threatening infections. The treatment is also a potential source of new cancer. Pages Unit Review 1. A 2. B 3. B 4. B 5. D 6. C 7. A 8. C Unit 5 Answer Key 5 Science Foundations 10

6 9. A 10. D 11. B 12. A 13. C 14. C 15. E 16. G* 17. A 18. B 19. F** 20. D 21. H*** 22. B 23. C 24. C * If you have an early edition of the book, no term in the list matches this or the existing description in the book. The appropriate term (mutation) was added to the list when the book was reprinted. The description was revised to read changes in reproductive cells caused by radiation. ** If you have an early edition of the book, no term in the list matches the description in the book. The appropriate term (daughter nucleus) was added to the list when the book was reprinted. *** If you have an early edition of the book, no term in the list matches this description. The appropriate term (fission) was added to the list when the book was reprinted. Unit 5 Answer Key 6 Science Foundations 10