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Background radiation, shielding, inverse-square law, radioactive decay

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- 1. Today: Inverse-square law, shielding, sources of radiation Sources of annual ionizing radiation dose of typical human
- 2. Quiz results Ouch!
- 5. Clicker question review—inverse square law <ul><li>Let’s say we know that if we stand 1 meter from a source of radiation that in 1 hour we will receive a dose of radiation equal to our normal background for one year. How far should we stand (approximately) so we receive the same dose in 16 hours ? </li></ul><ul><li>1/16 of a meter </li></ul><ul><li>¼ of a meter </li></ul><ul><li>4 meters </li></ul><ul><li>16 meters </li></ul>
- 6. Clicker question review—inverse square law <ul><li>Let’s say we know that if we stand 1 meter from a source of radiation that in 1 hour we will receive a dose of radiation equal to our normal background for one year. How far should we stand (approximately) so we receive the same dose in 16 hours ? </li></ul><ul><li>1/16 of a meter </li></ul><ul><li>¼ of a meter </li></ul><ul><li>4 meters </li></ul><ul><li>16 meters </li></ul>
- 7. The intensity of radiation follows the inverse square law Force Charge1 * Charge2 distance 2 Intensity of radiation Source intensity distance 2 Remember for electric charge: If you double the distance, Intensity decreases by a factor of 4
- 8. Inverse-square law demo Three pieces together are a “Geiger counter” Geiger-Müller tube High Voltage Power Supply Counter Radioactive Source Holder Calibrated distance rail
- 9. Refresher on Geiger counter Depending on the design: Maybe detect alpha-radiation CAN detect beta-radiation Maybe detect gamma-radiation Alpha particles difficulty passing through window But can make it through mica Ionizing radiation (beta, gamma, some alpha) enter through window and create ions inside. These events are detected via the electric current and turned into audible “clicks.”
- 10. Inverse-square law demo Geiger-Müller tube Radioactive Source Holder Calibrated distance rail Let’s try the experiment again from last week Distance
- 11. Three kinds of radiation emitted via radioactive decay named before they were understood…alpha, beta, gamma Alpha particles stopped by paper alpha particles are helium nuclei Beta particles stopped by aluminum beta particles are electrons (or positrons) Gamma rays stopped by lead gamma rays are high energy photons x-rays similar, but lower energy than gamma
- 12. Shielding demo Geiger-Müller tube Radioactive Source Holder Calibrated distance rail Let’s try experiments with different shielding materials Place different shielding materials here
- 13. Ionizing radiation is radiation with enough energy per particle to knock an electron off an atom ( ionize it) <ul><li>Electromagnetic radiation (no charge): </li></ul><ul><li>Gamma-rays, x-rays, UV radiation </li></ul><ul><li>Particle radiation (charged or uncharged): </li></ul><ul><li>Beta-radiation (electrons / positrons) </li></ul><ul><li>Alpha-radiation (helium nuclei) </li></ul><ul><li>Protons, neutrons, other particles </li></ul><ul><li>You can see that many of these types of ionizing radiation are produced from nuclear decay reactions </li></ul>
- 14. Clicker Question— Ionizing radiation <ul><li>Which of the following is not a type of ionizing radiation? </li></ul><ul><li>Microwave radiation </li></ul><ul><li>High-energy alpha particle </li></ul><ul><li>Gamma-ray </li></ul><ul><li>High-energy proton </li></ul><ul><li>X-ray </li></ul>
- 15. Clicker Question— Ionizing radiation <ul><li>Which of the following is not a type of ionizing radiation? </li></ul><ul><li>Microwave radiation </li></ul><ul><li>High-energy alpha particle </li></ul><ul><li>Gamma-ray </li></ul><ul><li>High-energy proton </li></ul><ul><li>X-ray </li></ul>Microwave photons DO NOT have enough energy to kick an electron out of an atom
- 16. Effects of ionizing radiation on living cells We care about ionizing radiation because it can induce chemical reactions <ul><li>Cells have proteins that can repair damaged DNA </li></ul><ul><ul><li>Very successful at doing so ( http://www.youtube.com/watch?v=te-NQG8Negk ) </li></ul></ul><ul><li>When DNA cannot be repaired either: </li></ul><ul><li>Cell death </li></ul><ul><li>Permanent mutation—This is what we usually worry about. </li></ul>Ionizing radiation creates radicals (reactive chemicals) in the water Radicals react with DNA to cause damage DNA Damage
- 17. NOTE: Some ionizing radiation is essential! <ul><li>Ultraviolet (UV) radiation is essential for the synthesis of vitamin D </li></ul><ul><li>It is becoming clear to many scientists that Vitamin D is essential for the body’s cancer defense mechanisms. </li></ul><ul><li>Many mainstream cancer biologists believe sun exposure has much more positive benefits than negatives (but still controversial) </li></ul>7-dehydrocholesterol pre-vitamin D 3
- 18. <ul><ul><li>Less than 300 mrem (or don’t know) </li></ul></ul><ul><ul><li>300-350 mrem </li></ul></ul><ul><ul><li>350-370 mrem (within 10 mrem of average) </li></ul></ul><ul><ul><li>370-400 mrem </li></ul></ul><ul><ul><li>Greater than 400 mrem </li></ul></ul>From the homework for today, what is your annual radiation dose?
- 19. <ul><ul><li>Natural (Radon, uranium, cosmic radiation) </li></ul></ul><ul><ul><li>Medical (x-rays, therapy, ...) </li></ul></ul><ul><ul><li> Man-made (smoke detectors, glow-in-the dark, ...) </li></ul></ul><ul><ul><li>Participation in nuclear catastrophes </li></ul></ul><ul><ul><li>Don’t know </li></ul></ul>For most people, what accounts for biggest fraction of annual radiation dose?
- 20. <ul><ul><li>Natural (Radon, uranium, cosmic radiation) </li></ul></ul><ul><ul><li>Medical (x-rays, therapy, ...) </li></ul></ul><ul><ul><li> Man-made (smoke detectors, glow-in-the dark, ...) </li></ul></ul><ul><ul><li>Participation in nuclear catastrophes </li></ul></ul><ul><ul><li>Don’t know </li></ul></ul>For most people, natural, unavoidable radiation is largest source. For most people, what accounts for biggest fraction of annual radiation dose?
- 21. Some Sources of Radiation Discussed (by Katie Richardson-McDaniel) <ul><li>Elevation: Albuquerque is at 5312 feet above sea level. </li></ul><ul><ul><ul><li>How does this effect our exposure to radiation? </li></ul></ul></ul><ul><ul><ul><li>Why would there be less radiation at sea level? </li></ul></ul></ul><ul><ul><li>This explains why plane flight hours matter, too </li></ul></ul>
- 22. <ul><li>Solar wind as a source of radiation: http://www.youtube.com/watch?v=w1DfOYl857w </li></ul><ul><ul><ul><li>Earth's magnetic field protects us from charged radiation only </li></ul></ul></ul><ul><ul><ul><ul><li>So elevation still matters for gamma radiation </li></ul></ul></ul></ul><ul><ul><ul><li>Space vehicles need to be built to withstand the radiation </li></ul></ul></ul><ul><ul><ul><li>Mars lost its magnetic field and consequently its atmosphere </li></ul></ul></ul>Some Sources of Radiation Discussed (by Katie Richardson-McDaniel)
- 23. <ul><li>Colorado Plateau: </li></ul><ul><ul><ul><li>Deposits of Uranium </li></ul></ul></ul><ul><li>Higher doses of Radon </li></ul><ul><li>30% of homes in ABQ </li></ul><ul><li>contain indoor radon levels </li></ul><ul><li>over the EPA action level, </li></ul><ul><li>compared to 10-12% </li></ul><ul><li>of homes for the entire </li></ul><ul><li>US. </li></ul><ul><li>Indoor radon contributes </li></ul><ul><li>about 100–300 mrem/yr. </li></ul><ul><li>Q:Is this why we don’t have basements in Albuquerque? </li></ul>Some Sources of Radiation Discussed (by Katie Richardson-McDaniel)
- 24. We are always surrounded by significant natural sources of ionizing radiation <ul><li>Interestingly, our own bodies are radioactive! </li></ul><ul><li>Counter-intuitively, the human impact on average background radiation is negligible. But of course, human events can cause huge local / acute doses </li></ul><ul><li>So: It is reasonable that humans could perform nuclear reactions while having negligible impact to the average radiation exposure </li></ul>People in Ramsar, Iran have 100x the background dose that we do here!
- 25. Clicker question—Radioactive shielding <ul><li>Based upon what you know about the types and sources of ionizing radiation and radiation shielding: </li></ul><ul><li>If you build a bunker out of lead 10 meters thick, and go inside the bunker, can you shield your body from all ionizing radiation? </li></ul><ul><li>Yes </li></ul><ul><li>No </li></ul>
- 26. Clicker question—Radioactive shielding <ul><li>Based upon what you know about the types and sources of ionizing radiation and radiation shielding: </li></ul><ul><li>If you build a bunker out of lead 10 meters thick, and go inside the bunker, can you shield your body from all ionizing radiation? </li></ul><ul><li>Yes </li></ul><ul><li>No </li></ul>For one thing, your own body is radioactive!
- 27. Parallel of electrical energy with nuclear energy Electricity and radioactivity have existed since the beginning of time So, the dangers have always been present, and always will be. Humans have learned how to harness the powers of electricity and nuclear reactions…presenting new dangers along with great benefits The task for society is to weigh the benefits against the dangers Hey toddlers! I’m your friend!
- 28. How to read the short-hand summary of an isotope Number of protons Atomic number (Z) Total number of nucleons (protons + neutrons) Mass number (A) Element symbol The atomic number and element symbol provide the same information. I.e., Carbon always has 6 protons. So, this isotope is also written: 12 C or Carbon-12 C 12 6
- 29. In chemical reactions , these items do not change Atomic number (Z) is constant Mass number (A) is constant Element does not change If any of these values change, then it is a nuclear reaction! Transmutation of an Element C 12 6
- 30. Examples of nuclear reactions U 238 92 Th 234 90 He 4 2 (Plus a lot of kinetic energy) Alpha-decay n 1 0 N 14 7 Neutron capture p 1 1 C 14 6 (This reaction happens in the upper atmosphere to produce Carbon-14)
- 31. Clicker question—Beta Decay <ul><li>In one kind of beta decay , a neutron in a nucleus can transform into a proton, emitting an electron (beta radiation) and an electron neutrino. What kind of transmutation of the element occurs? </li></ul><ul><li>The remaining atom has an atomic number TWO LESS than before </li></ul><ul><li>The remaining atom has an atomic number ONE LESS than before </li></ul><ul><li>The remaining atom has an atomic number SAME as before </li></ul><ul><li>The remaining atom has an atomic number ONE MORE than before </li></ul><ul><li>The remaining atom has an atomic number TWO MORE than before </li></ul>
- 32. Clicker question—Beta Decay <ul><li>In one kind of beta decay , a neutron in a nucleus can transform into a proton, emitting an electron (beta radiation) and an electron neutrino. What kind of transmutation of the element occurs? </li></ul><ul><li>The remaining atom has an atomic number TWO LESS than before </li></ul><ul><li>The remaining atom has an atomic number ONE LESS than before </li></ul><ul><li>The remaining atom has an atomic number SAME as before </li></ul><ul><li>The remaining atom has an atomic number ONE MORE than before </li></ul><ul><li>The remaining atom has an atomic number TWO MORE than before </li></ul>
- 33. Let’s understand beta-decay a little more by learning a bit about particle physics

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