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- 1. Smart Women in Physics Together: Undergraduate Mentoring <ul><ul><li>Ask female graduate students all of your questions about </li></ul></ul><ul><ul><li>majoring in physics </li></ul></ul><ul><ul><li>applying for graduate school </li></ul></ul><ul><ul><li>being a woman in physics! </li></ul></ul><ul><ul><li>Friday, April 10 th at 2:30pm </li></ul></ul><ul><ul><li>Winnings Coffee </li></ul></ul><ul><ul><li>West side of Harvard, South of Central </li></ul></ul><ul><ul><li>Funded by the GPSA Project Committee </li></ul></ul>
- 2. Today: Radiation Dose Definitions, Medical Applications, PET scan 3-D rendering Source: wikipedia
- 3. Small group exercise! <ul><li>I place on the table a small piece of material and say, “this is radioactive.” </li></ul><ul><li>How many different properties of the material can you think of that you would want to characterize, in order to know everything about its radioactivity? </li></ul><ul><li>Form small groups, and brainstorm. Have a leader / spokesperson write down results. </li></ul>?
- 4. <ul><li>What kind of radiation is emitted? Alpha, beta, gamma. </li></ul><ul><li>Mass/weight </li></ul><ul><li>“ half-life” (time for ½ to decay) </li></ul><ul><li>Color…? </li></ul><ul><li>Temperature… </li></ul><ul><li>What is the element? </li></ul>
- 5. Measuring the amount of radioactivity or dose <ul><li>We can think about amount of radiation in two ways. </li></ul><ul><li>Describe the source of radiation </li></ul><ul><ul><li>Physics-based, rigorous </li></ul></ul><ul><li>Describe the absorbed radiation dose </li></ul><ul><ul><li>Complicated biology and other factors </li></ul></ul>
- 6. There are rigorous ways to characterize the source of radiation <ul><li>What type of radiation does the material emit? </li></ul><ul><ul><li>X-rays, gamma rays, beta radiation, alpha particles </li></ul></ul><ul><li>How much radiation per second? </li></ul><ul><ul><li>curies, becquerels, counts per second </li></ul></ul><ul><li>What is the half-life of the material? </li></ul><ul><ul><li>Minutes, days, years, … </li></ul></ul><ul><li>What is the average energy per particle or ray emitted? </li></ul>
- 7. There are rigorous ways to characterize the source of radiation <ul><li>What type of radiation does the material emit? </li></ul><ul><ul><li>X-rays, gamma rays, beta radiation, alpha particles </li></ul></ul><ul><li>How much radiation per second? </li></ul><ul><ul><li>curies, becquerels, counts per second </li></ul></ul><ul><li>What is the half-life of the material? </li></ul><ul><ul><li>Minutes, days, years, … </li></ul></ul><ul><li>What is the average energy per particle or ray emitted? </li></ul>
- 8. There are two main units of radioactivity <ul><li>The becquerel (Bq) is defined as one radioactive decay event per second </li></ul><ul><ul><li>1 Bq = 1 reaction / second </li></ul></ul><ul><li>The curie (Ci) is based on the radioactivity of about 1 gram of radium-226 </li></ul><ul><ul><li>1 Ci = 37 billion Bq = 37 billion reactions / second </li></ul></ul>Marie Curie Nobel prizes in Physics and Chemistry Henri Becquerel Nobel Prize in Physics Example: 1 kilogram of “typical” soil has 400 Bq of Potassium-40 -- or 11 nanocuries
- 9. There are rigorous ways to characterize the source of radiation <ul><li>What type of radiation does the material emit? </li></ul><ul><ul><li>X-rays, gamma rays, beta radiation, alpha particles </li></ul></ul><ul><li>How much radiation per second? </li></ul><ul><ul><li>curies, becquerels, counts per second </li></ul></ul><ul><li>What is the half-life of the material? </li></ul><ul><ul><li>Minutes, days, years, … </li></ul></ul><ul><li>What is the average energy per particle or ray emitted? </li></ul>
- 10. Radioactive decay is a random process P P P P P P P P P P P P P P P P P P U P P U P P P P U P U U P P P P P P S S S S S U P U U P P P P P U U P U P P U P S S S S S S S U P U U P P P U P U U P U U P U P S S S S S S S S S 10 days 20 days 30 days Example: Phosphorus-32 decay into Sulfur-32
- 11. Half-life is the average amount of time for ½ of the atoms to decay <ul><li>P-32 half life ~14 days </li></ul><ul><li>Decay rate is proportional to the number of radioactive atoms remaining </li></ul><ul><li>So, radioactivity of a sample decreases with the same half-life </li></ul><ul><li>Applets: http://www.colorado.edu/physics/2000/isotopes/radioactive_decay3.html </li></ul><ul><li>http://lectureonline.cl.msu.edu/~mmp/applist/decay/decay.htm </li></ul>
- 12. Radioactivity (becquerels) and Half-life are inversely related <ul><li>Longer half-life = lower radioactivity </li></ul><ul><ul><li>Stable isotope has an infinite half-life </li></ul></ul><ul><li>Shorter half-life = higher radioactivity </li></ul><ul><ul><li>Highly radioactive isotopes will disappear quickly </li></ul></ul>
- 13. Clicker Question—Half life / radioactivity <ul><li>Let’s say you have two samples, each with the same number of atoms in them. </li></ul><ul><li>Sample “A” has half-life of two weeks. </li></ul><ul><li>Sample “B” has half-life of 4 billion years. </li></ul><ul><li>Which will have a higher radioactivity? </li></ul><ul><li>A or B </li></ul>
- 14. Clicker Question—Half life / radioactivity <ul><li>Let’s say you have two samples, each with the same number of atoms in them. </li></ul><ul><li>Sample “A” has half-life of two weeks. </li></ul><ul><li>Sample “B” has half-life of 4 billion years. </li></ul><ul><li>Which will have a higher radioactivity? </li></ul><ul><li>A or B </li></ul>Shorter half-life = higher radioactivity If the half-life is infinite, it is not radioactive
- 15. There are rigorous ways to characterize the source of radiation <ul><li>What type of radiation does the material emit? </li></ul><ul><ul><li>X-rays, gamma rays, beta radiation, alpha particles </li></ul></ul><ul><li>How much radiation per second? </li></ul><ul><ul><li>curies, becquerels, counts per second </li></ul></ul><ul><li>What is the half-life of the material? </li></ul><ul><ul><li>Minutes, days, years, … </li></ul></ul><ul><li>What is the average energy per particle or ray emitted? </li></ul>
- 16. The energy per emitted particle indicates how deeply it can penetrate materials and how much damage it can do <ul><li>Examples: </li></ul><ul><ul><li>P-32 beta 1.7 megaelectronvolts (MeV) </li></ul></ul><ul><ul><li>Ra-226 alpha 4.9 MeV </li></ul></ul><ul><ul><li>Rn-222 alpha 5.6 MeV </li></ul></ul><ul><ul><li>K-40 beta 1.3 MeV </li></ul></ul><ul><li>However, the type of radiation (alpha, beta, gamma, neutron) tends to be more important </li></ul>Mega = 10^6 or 1 million
- 17. Clicker question—classifying radiation <ul><li>If held 1 inch away from your body, which radiation source is more likely to cause cancer? </li></ul><ul><li>Source with radioactivity of 1 million becquerels (Bq) </li></ul><ul><li>Source with radioactivity of 1 billion becquerels (Bq) </li></ul><ul><li>Impossible to determine </li></ul>
- 18. Clicker question—classifying radiation <ul><li>If held 1 inch away from your body, which radiation source is more likely to cause cancer? </li></ul><ul><li>Source with radioactivity of 1 million becquerels (Bq) </li></ul><ul><li>Source with radioactivity of 1 billion becquerels (Bq) </li></ul><ul><li>Impossible to determine </li></ul>There are many other things you would need to know: What type of radiation do each emit? Is there any shielding in between?
- 19. Results of homework assignment
- 20. A few homework responses Adrian: If I became a luddite and lived in a hut in the woods at sea level I might save myself 80 mrem or so. Laura: Only 2.010 mrem or 0.6 % of my annual radiation exposure can be attributed to man made sources David: Unavoidable background radiation is from food and water, there is absolutely nothing I can do to change that.
- 21. Measuring the amount of radioactivity or dose <ul><li>We can think about amount of radiation in two ways. </li></ul><ul><li>Describe the source of radiation </li></ul><ul><ul><li>Physics-based, rigorous </li></ul></ul><ul><li>Describe the absorbed radiation dose </li></ul><ul><ul><li>Complicated biology and other factors </li></ul></ul>
- 22. Classifying the radiation dose is very complicated <ul><li>Biological effects depend on acute versus chronic dose </li></ul><ul><li>Interaction of radiation with cells has a number of possible outcomes…depends on numerous factors </li></ul><ul><ul><ul><li>Characteristics of the radiation </li></ul></ul></ul><ul><ul><ul><li>Characteristics of the biological system (e.g. general level of health) </li></ul></ul></ul><ul><li>Nevertheless, attempts are made to define dose </li></ul>
- 23. Radiation doses <ul><li>In terms of energy, absorbed dose is measured in grays (Gy) </li></ul><ul><ul><li>1 Gy = 1 joule per kilogram of material </li></ul></ul><ul><li>Biological dose is measured in sieverts (Sv) or rem </li></ul><ul><ul><li>1 Sv = effect of 1 joule per kilogram </li></ul></ul><ul><ul><li>1 Sv = 100 rem </li></ul></ul><ul><ul><li>1 sievert = Q * gray “Q” is some fudge factor </li></ul></ul><ul><li>For photons (x-ray, gamma) Q = 1 </li></ul><ul><li>Beta rays, Q = 1 </li></ul><ul><li>Low energy neutrons, Q = 5; medium energy Q = 20; high energy Q=5 </li></ul><ul><li>Alpha, Q = 20 </li></ul>
- 25. Some relevant radiation dose values <ul><li>Acute radiation dose </li></ul><ul><ul><li>About 3 Sv (whole body) will cause radiation poisoning and 50% chance of death. </li></ul></ul><ul><ul><li>Medical imaging procedures typically in the milli-sievert range </li></ul></ul><ul><li>Chronic radiation dose </li></ul><ul><ul><li>Natural background about 2.4 milli-Sv per year </li></ul></ul><ul><ul><li>What dose will cause cancer? Difficult to determine and also random . </li></ul></ul>
- 26. Medical applications of radiation Destruction: Radiation Therapy Imaging: X-rays Imaging: Positron emission tomography Imaging: Gastrointestinal imaging
- 27. Positron emission tomography (PET scanning)
- 28. Radiation Therapy <ul><li>Extremely high but localized dose, meant to destroy tumor cells. </li></ul><ul><li>20 or more localized grays </li></ul><ul><li>Also a “whole body” dose for killing immune system prior to bone-marrow transplant. </li></ul><ul><li>~ 10 grays (3 usually lethal) </li></ul>
- 29. Some slides about cancer radiation therapy http://youtube.com/watch?v=ZtENJI1K1hA&feature=related
- 30. Clicker Question—Acute Radiation Dose <ul><li>I said earlier that a dose of about 3 sieverts (Sv) will kill someone about 50% of the time. Let’s say someone is exposed to 100 sieverts of radiation. Can you say almost certainly they will die? </li></ul><ul><li>YES! </li></ul><ul><li>No! </li></ul>
- 31. Clicker Question—Acute Radiation Dose <ul><li>I said earlier that a dose of about 3 sieverts (Sv) will kill someone about 50% of the time. Let’s say someone is exposed to 100 sieverts of radiation. Can you say almost certainly they will die? </li></ul><ul><li>YES! </li></ul><ul><li>No! </li></ul>The information is not specific enough. If it happens over the whole body in a short time, then probably YES… However, if it happens over 100 years, then probably not. Also if localized, also will not die There is no easy way to put a concrete number on radiation dose
- 32. Ionizing radiation almost NEVER makes something turn radioactive! <ul><li>In order for an object to become radioactive, the nuclei in the atoms must change…”nuclear reactions” required. </li></ul><ul><li>Typically: </li></ul><ul><li>Neutrons are the most effective at causing nuclear transmutation… </li></ul><ul><li>Radiactive decay very rarely releases neutrons </li></ul>The person does NOT become radioactive … his nuclei are unchanged Nuclear reaction Releases ionizing radiation Causes Chemical reactions
- 33. Clicker question--transmutation <ul><li>Food irradiation or “cold pasteurization” often uses gamma rays to kill any microorganisms in the food. There are no neutrons involved. </li></ul><ul><li>Does the food then become radioactive (only mildly, though)? </li></ul><ul><li>Yes </li></ul><ul><li>No </li></ul>
- 34. Clicker question--transmutation <ul><li>Food irradiation or “cold pasteurization” often uses gamma rays to kill any microorganisms in the food. There are no neutrons involved. </li></ul><ul><li>Does the food then become radioactive (only mildly, though)? </li></ul><ul><li>Yes </li></ul><ul><li>No </li></ul><ul><li>There are safety concerns, but NOT because of radioactive food! We can understand the physics </li></ul><ul><li>The risks need to be balanced against the benefits…In US: </li></ul><ul><ul><li>325,000 hospitalized per year from food poisoning! </li></ul></ul><ul><ul><li>5,000 deaths / year! </li></ul></ul>
- 35. Protons and neutrons are made of quarks Quark model of a proton www2.cnrs.fr/presse/communique/709.htm “ Up” quarks charge = + 2/3 each “ Down” quark -1/3 charge Arpad Horvath Quark model of neutron
- 36. Quarks and Leptons are the constituent parts of matter. Murray Gell-Mann Nobel Prize 1969 There are six quarks Up Charmed Top Down Strange Bottom Charge = +2/3 Charge = -1/3 Similarly, there are six leptons Increasing mass Electron Muon Tau Electron neutrino Muon neutrino Tau neutrino Antimatter consists of the 6 anti-particle quarks and 6 anti-particle leptons
- 37. Under normal conditions, quarks do not exist in free space. Fermilab particle accelerator Billion-dollar physics experiments were required to detect quarks for fleeting instants in time
- 38. Beta-decay can transform a neutron into a proton Quarks (Electron) It is a decay of a “down quark” into an “up quark”
- 39. Clicker question--Quarks <ul><li>An up quark has an electric charge of +2/3. </li></ul><ul><li>A down quark has an electric charge of -1/3. </li></ul><ul><li>Which of the following combinations would a proton consist of? </li></ul><ul><li>Up, up, up </li></ul><ul><li>Down, down, down </li></ul><ul><li>Up, down, down </li></ul><ul><li>Up, up, down </li></ul><ul><li>Up, up, down, down </li></ul>
- 40. Clicker question--Quarks <ul><li>An up quark has an electric charge of +2/3. </li></ul><ul><li>A down quark has an electric charge of -1/3. </li></ul><ul><li>Which of the following combinations would a proton consist of? </li></ul><ul><li>Up, up, up </li></ul><ul><li>Down, down, down </li></ul><ul><li>Up, down, down </li></ul><ul><li>Up, up, down </li></ul><ul><li>Up, up, down, down </li></ul>+2/3 +2/3 -1/3 Take home message about quarks: Nucleons are composed of three quarks. Particle Physicists can predict a lot about matter from the quark / lepton models, Including some radioactive decay properties

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