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Lecture December 6


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Lecture December 6

  1. 1. RadiationRadiation
  2. 2. What makes somethingWhat makes something radioactive?radioactive?  The nucleus of anThe nucleus of an atom contains protonsatom contains protons and neutronsand neutrons  They are packedThey are packed together with a lot oftogether with a lot of repulsive chargerepulsive charge – Opposites attract, sameOpposites attract, same charges repelcharges repel  If atom has too fewIf atom has too few neutrons, positronneutrons, positron emission occursemission occurs  If atom has tooIf atom has too many neutrons,many neutrons, beta emissionbeta emission occursoccurs  Another type ofAnother type of radioactive decay isradioactive decay is loss of anloss of an αα particleparticle
  3. 3. Examples of RadioactiveExamples of Radioactive decaydecay
  4. 4. Band of StabilityBand of Stability  Notice mostNotice most elements are stableelements are stable & elements& elements possess a drivingpossess a driving force to try toforce to try to become stablebecome stable
  5. 5. RadioactivityRadioactivity  There are 114 or so elements & 340There are 114 or so elements & 340 isotopes of all the elements, onlyisotopes of all the elements, only about 70 are radioactiveabout 70 are radioactive  All isotopes with atomic numbersAll isotopes with atomic numbers greater than 83 are radioactivegreater than 83 are radioactive  Most are not significant contributors toMost are not significant contributors to our overall radiation dose because ofour overall radiation dose because of their low abundancetheir low abundance
  6. 6. Naturally occurringNaturally occurring radiationradiation  Travel from LosTravel from Los Angeles to Paris on aAngeles to Paris on a conventional flight willconventional flight will result in additional 10result in additional 10 millirems of radiationmillirems of radiation  1. Cosmic radiation:1. Cosmic radiation: At sea level averageAt sea level average annual dose is 26annual dose is 26 millirem a yearmillirem a year
  7. 7. Naturally occurringNaturally occurring radiationradiation  2. Cosmogenic radiation: Most2. Cosmogenic radiation: Most common iscommon is 1414 C Contributes 1 milliremC Contributes 1 millirem per yearper year  Nuclear reaction:Nuclear reaction: Carbon 14 has a half life of 5730 yearsCarbon 14 has a half life of 5730 years & decays by beta emission& decays by beta emission
  8. 8. Half lifeHalf life  What is a half life?What is a half life? – The amount of time for half of theThe amount of time for half of the remaining material to decay.remaining material to decay.
  9. 9. Half lives illustratedHalf lives illustrated  After 5730 years (1 halfAfter 5730 years (1 half life) there is half a pielife) there is half a pie leftleft  Imagine the pie is someImagine the pie is some radioactive carbon 14,radioactive carbon 14, originally there is one pieoriginally there is one pie worth of carbon 14worth of carbon 14
  10. 10. Half lives illustratedHalf lives illustrated  After 11,460 years (2After 11,460 years (2 half lives) there is ¼ ofhalf lives) there is ¼ of a pie lefta pie left  After 17,190 years, 1/8After 17,190 years, 1/8 of the pie is leftof the pie is left  Notice the absoluteNotice the absolute amount of material thatamount of material that is lost gets smaller andis lost gets smaller and smaller the greater # ofsmaller the greater # of half liveshalf lives
  11. 11. Half livesHalf lives  If the pie illustrated here was allIf the pie illustrated here was all 1414 CC and it originally weighed 750 g, howand it originally weighed 750 g, how many grams would be remaining aftermany grams would be remaining after 22,920 years?22,920 years?
  12. 12. Naturally occurringNaturally occurring radiationradiation  3. Terrestrial radiation: Arises from3. Terrestrial radiation: Arises from radioisotopes whose half lives areradioisotopes whose half lives are comparable to the age of the earth,comparable to the age of the earth, most comes from uranium seriesmost comes from uranium series Annual dose 28 mrem externally &Annual dose 28 mrem externally & 240 mrem internally240 mrem internally  Radon gas is another importantRadon gas is another important source heresource here
  13. 13. RadonRadon  Enters buildings through dirtEnters buildings through dirt floors, cracks, floor drains, andfloors, cracks, floor drains, and from building materials likefrom building materials like gypsum and stone fireplacesgypsum and stone fireplaces  Small amounts are dissolved in groundwaterSmall amounts are dissolved in groundwater and in natural gas suppliesand in natural gas supplies
  14. 14. Radon continuedRadon continued  Radon isotopes have a fairly short halfRadon isotopes have a fairly short half life but they decay to insoluble solidslife but they decay to insoluble solids that can get deposited in lungsthat can get deposited in lungs  Radon is most problematic in tight,Radon is most problematic in tight, well sealed basements in the winter,well sealed basements in the winter, little air flowlittle air flow  EPA estimates radon contributesEPA estimates radon contributes 14,000 deaths per year from lung14,000 deaths per year from lung cancercancer
  15. 15. Radon half-life problemRadon half-life problem  222222 Rn has a half life of 3.8 days. If thereRn has a half life of 3.8 days. If there is 40.0 grams ofis 40.0 grams of 222222 Rn and it is allowedRn and it is allowed to decay 11.4 days, how much willto decay 11.4 days, how much will remain?remain?
  16. 16. Radiation from consumerRadiation from consumer productsproducts  Radioluminescent paintRadioluminescent paint  Radioluminescent signsRadioluminescent signs  Camping lantern mantlesCamping lantern mantles  Smoke detectorsSmoke detectors  Ceramics and glasswareCeramics and glassware  Salt substituteSalt substitute  Tobacco productsTobacco products
  17. 17. Distribution of SourcesDistribution of Sources of Radiation Exposureof Radiation Exposure Source Natural Sources Exposure (%) Radon 55 Cosmic radiation 8 Terrestrial radiation 8 Internal radiation 11
  18. 18. Distribution of SourcesDistribution of Sources of Radiation Exposureof Radiation Exposure Source Man-made sources Exposure (%) Medical x-rays 11 Nuclear medicine 4 Consumer products 3 Occupational exposure, nuclear fallout, nuclear fuel cycle, other sources <1
  19. 19. Typical doseTypical dose  360 mrem per year is average dose360 mrem per year is average dose each person can expect, 82% iseach person can expect, 82% is natural, 18% is man-madenatural, 18% is man-made
  20. 20. Radiation & SafetyRadiation & Safety ContinuedContinued  Type of radiationType of radiation also importantalso important  αα particles can beparticles can be stopped by skinstopped by skin  ββ particles can beparticles can be stopped by Al foilstopped by Al foil  γγ rays are ultimatelyrays are ultimately most dangerous,most dangerous, dominant problemdominant problem in nuclear wastein nuclear waste  Half lifeHalf life  ShorterShorter half life will emit morehalf life will emit more of its radiation over aof its radiation over a given period of timegiven period of time  131131 I half life of 8 daysI half life of 8 days  238238 U half life of 4.5U half life of 4.5 billion yearsbillion years
  21. 21. RadiationRadiation
  22. 22. Nuclear ApplicationsNuclear Applications  Far more lives haveFar more lives have been saved frombeen saved from nuclear chemistrynuclear chemistry than have beenthan have been lost, even includinglost, even including Nagasaki andNagasaki and HiroshimaHiroshima  Nuclear Medicine isNuclear Medicine is used in diagnosis ofused in diagnosis of cancers and othercancers and other diseases also used indiseases also used in treatment of diseasestreatment of diseases
  23. 23. Food irradiationFood irradiation  E. coli bacteria has killed numerousE. coli bacteria has killed numerous people and sickened thousands ofpeople and sickened thousands of times moretimes more  Food spoilage can sometimes accountFood spoilage can sometimes account for 50% food lossfor 50% food loss  Food irradiation can prevent or lessenFood irradiation can prevent or lessen both thingsboth things
  24. 24. What is food irradiation?What is food irradiation?  Uses gamma raysUses gamma rays fromfrom 6060 Co orCo or 137137 CsCs  Irradiates the food,Irradiates the food, effectively killingeffectively killing bacteria such asbacteria such as Trichinella andTrichinella and SalmonellaSalmonella  Does not cause theDoes not cause the food to becomefood to become radioactive!radioactive!