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The ABC's (or Alpha, Beta, Gamma) of Radioactivity

The ABC's (or Alpha, Beta, Gamma) of Radioactivity. Expectations. SWBAT state what radioactivity is, where these rays come from, what each ray is made of and state why they are dangerous. SWABT to explain the meaning of “half-life”. Early Pioneers in Radioactivity. Rutherford:

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The ABC's (or Alpha, Beta, Gamma) of Radioactivity

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  1. The ABC's (or Alpha, Beta, Gamma) of Radioactivity Science Park HS -- Honors Chemistry

  2. Expectations • SWBAT state what radioactivity is, where these rays come from, what each ray is made of and state why they are dangerous. • SWABT to explain the meaning of “half-life”. Science Park HS -- Honors Chemistry

  3. Early Pioneers in Radioactivity Rutherford: Discoverer Alpha and Beta rays 1897 Roentgen: Discoverer of X-rays 1895 The Curies: Discoverers of Radium and Polonium 1900-1908 Becquerel: Discoverer of Radioactivity 1896 Science Park HS -- Honors Chemistry

  4. Review of Key Definitions • Atomic Number: It’s the Number of Protons in the nucleus of an Atom. • Nucleus: It’s where the Protons and Neutrons are located in an Atom. • Protons: Positively Charged Particles in the Nucleus of the atom. Mass = (approx) 1 AMU • Neutrons: Neutrally charged particles in the nucleus of an atom Mass = (approx) 1 AMU • Mass Number of an atom: Number of Protons + Number of Neutrons in the nucleus of an atom. Science Park HS -- Honors Chemistry

  5. What do we mean by Radioactivity? Radioactive decayis the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. • ~An unstable atomic nucleus emits a form of radiation (alpha, beta, or gamma) to become stable. • ~A radioactive nucleus actually decays into a different atom. (= different # of protons ).

  6. What do we mean by Radioactivity? But, why does radioactivity occur? An unstable nucleus releases energy (emitting particles & Electromagnetic waves) to become more stable (and becomes a new type of atom) What makes a nucleus unstable? A nucleus is unstable because of the ratio of protons to neutron in the nucleus of an atom. (Ratio outside of the Stability belt) Science Park HS -- Honors Chemistry

  7. The Nuclear StabilityBelt Ratio of neutrons to protons in the nucleus 138 Neutrons 92 Protons Neutrons Protons 6 Neutrons 6 Protons Science Park HS -- Honors Chemistry

  8. Kinds of Radioactivity The three main decays are Alpha, Beta and Gamma Science Park HS -- Honors Chemistry

  9. Science Park HS -- Honors Chemistry

  10. Three Common Types of Radioactive Emissions Beta Alpha 3H  3He + 0β 241Am  237Np + 4He 2 1 2 -1 95 93 Gamma

  11. Three Common Types of Radioactive Emissions - Penetrability Alpha particles may be completely stopped by a sheet of paper, Beta particles by aluminum shielding. Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead. Science Park HS -- Honors Chemistry

  12. Radioactive Decay Law • Radioactive decay is the spontaneous release of energy in the form of radioactive particles or waves. • It results in a decreaseof the original amount radioactive material over time -(the unstable nuclei become stable by releasing the particles & waves)

  13. Radioactive Decay Law • Any radioactive isotope consists of a vast number of radioactive nuclei. • Nuclei does not decay all at once. • Decay over a period of time. • We can not predict when it will decay, its a random process but... 6

  14. Radioactive Decay Law ... We can determine, based on probability, approximately how many nuclei in a sample will decay over a given time period, by asuming that each nucleus has the same probability of decaying in each second it exists. 7

  15. The equation for the radioactive decay law: POF!!! • ∆N = - λN ∆ t

  16. What was that??? • Nt=the number of nuclei present at a give time (t) • N0= the number of nuclei present at time (t = 0) • e = is the natural expoentional (logarithms) • t = time (years, days, hours, or seconds) • λ = half life (a RATE of decay = amount/time) 16

  17. Half-Life (λ): The amount of time required for one-half or 50% of the radioactive atoms to undergo a radioactive decay. • Every radioactive element (isotope/nuclide) has a specific half-life associated with it. • Is a measure of how stable the nuclei is. • Half-Life ranges from fractions of a second to billions of years. • No operation or process of any kind (i.e., chemical or physical) has ever been shown to change the rate at which a radionuclide decays.

  18. 238U λ = 4,510,000,000 Years

  19. How long is the half-life of Sodium-24?

  20. Each half life is the SAME time interval

  21. Radioactivity • An unstable atomic nucleus emits a form of radiation (alpha, beta, or gamma) to become stable. • In other words, the nucleus decays into a different atom.

  22. Half-Life • Amount of time it takes for one half of a sample of radioactive atoms to decay

  23. Half-Life Calculation 400 200 5 min • You have 400 mg of a radioisotope with a half-life of 5 minutes. How much will be left after 30 minutes? 100 5 min 50 5 min 25 5 min 12.5 5 min 6.25 5 min 3.125 5 min 1.5625 5 min .78125 5 min

  24. Medical Applications of Half-Life

  25. Sources of Radioactivity • Primordial- from before the creation of the Earth (older than the earth) • Cosmogenic- formed as a result of cosmic ray interactions (from space) • Human produced - enhanced or formed due to human actions (minor amounts compared to natural) Science Park HS -- Honors Chemistry

  26. Where are the Sources of Radioactivity? • Naturally Occurring Sources: • Radon from the decay of Uranium and Thorium • Potassium -40 – found in minerals and in plants • Carbon 14 – Found in Plants and Animal tissue • Manmade Sources: • Medical use of Radioactive Isotopes • Certain Consumer products –(eg Smoke detectors) • Fallout from nuclear testing • Emissions from Nuclear Power plants Science Park HS -- Honors Chemistry

  27. Science Park HS -- Honors Chemistry

  28. Radiation Exposure to Americans Science Park HS -- Honors Chemistry

  29. Radioactivity – Is it a Health Problem? • The Alpha, Beta and Gamma particles all add energy to the body’s tissues. The effect is called the Ionizing Energy. It can alter DNA. • Even though Alpha particles are not very penetrative if the decaying atom is already in the body (inhalation, ingestion) they can cause trouble. • The Time, Distance and Shielding principle Science Park HS -- Honors Chemistry

  30. Summary/Questions • Why does a nucleus decay? • Order these emissions from least to greatest penetrability: Gamma, Alpha, Beta. • What is the greatest source of exposure to radioactivity in our everyday lives? • If I tell you that that the half-life of Fellmanium-250 is 10 days, how much would be left after 30 days if I started with 1600 atoms? Science Park HS -- Honors Chemistry

  31. FUSION AND FISSION

  32. THE SUN Every second, the sun converts 500 million metric tons of hydrogen to helium. Due to the process of fusion, 5 million metric tons of excess material is converted into energy in each second. This means that every year, 157,680,000,000,000 metric tons are converted into energy.

  33. Nuclear Fusion • Nuclear fusionis the process by which multiple nuclei join together to form a heavier nucleus. • It is accompanied by the release or absorption of energy depending on the masses of the nuclei involved..

  34. NEUTRON DEUTERIUM FUSION HELIUM TRITIUM http://fusioned.gat.com

  35. Complete the Fusion Reactions 4Be 1H 2He 6C 2He 1H 6C 2He 4Be 8O 2He 2He

  36. What process creates energy in the Sun? Fusion of hydrogen into helium in the Sun’s core generates the Sun’s energy. How long ago did fusion generate the energy we now receive as sunlight? Fusion created the energy we receive today about a million years ago. This is the time it takes for photons and then convection to transport energy through the solar interior to the photosphere. Once sunlight emerges from the photosphere, it takes only about 8 minutes to reach Earth.

  37. Fusion Changes Mass into Energy 1kg Hydrogen .993 kg Helium He What happened to the 0.007 kg? E=mc2 =(0.007kg) (3.0x108m/s)2 H = 630,000,000,000,000 J

  38. NUCLEAR FISSION Nuclear Fission - a reaction in which an atomic nucleus of a radioactive element splits by bombardmentfrom an external source, with simultaneous release of large amounts of energy. (used for electric power generation & nuclear weapons)

  39. Neutron induced in U235 Nuclear Fission Fission is Exothermic The sum of the masses of the resulting nuclei is less than the original mass (about 0.1% less) The “missing mass” is converted to energy according to E=mc2

  40. Neutrons may: • Creates two smaller nuclides and free neutrons • The free neutrons potentially collide with nearby U235 nuclei • May cause the nuclide to split as well 1 - Cause another fission by colliding with a U235 nucleus Each split (fission) is accompanied by a large quantity of E-N-E-R-G-Y

  41. U.S. Electrical Power Production by Source Source: EIA (2004)

  42. Nuclear Fuel Costs • Nuclear Fuel Costs Include • Uranium • Enrichment • Manufacturing • Waste Disposal • Total Nuclear Fuel Cost is Only About 0.5 cents per kilowatt-hour • Uranium accounts for only about 20% of this cost or 0.1 cents per kilowatt-hour • Increasing Uranium Cost has Minimal Impact

  43. Review Nuclear fission: - A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process Nuclear fusion: - Several small nuclei fuse together and release energy.

  44. Draw a Double Bubble Map of Fusion and Fission fission fusion Differences Similarities Differences

  45. Where to Get More Information • http://www.physics.isu.edu/radinf/natural.htm • EPA (Environmental Protection Agency) • Dept of Energy Science Park HS -- Honors Chemistry

  46. THE END!!! • Resources: • http://cathylaw.com/images/halflifebar.jpg • http://burro.astr.cwru.edu/Academics/Astr221/HW/HW3/noft.gif • http://www.chem.ox.ac.uk/vrchemistry/Conservation/page35.htm • www.gcse.com/ radio/halflife3.htm • www.nucmed.buffalo.edu/.../ sld003.htm • http://www.iem-inc.com/prhlfr.html • http://www.math.duke.edu/education/ccp/materials/diffcalc/raddec/raddec1.html • http://www.mrgale.com/onlhlp/nucpart/halflife.htm

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