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

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Science Park HS -- Honors Chemistry The ABC's (or Alpha, Beta, Gamma) of Radioactivity Slide 2 Science Park HS -- Honors Chemistry Agenda Definition of Radioactivity and emissions Discussion of the three most important types of emissions What do we mean by half-life? Where is Radioactivity encountered? Is Radioactivity dangerous? Slide 3 Science Park HS -- Honors Chemistry Expectations SWBAT state what radioactivity is, where these rays come from, what each ray is made of and state why they are dangerous. SWBAT identify 4 pioneer scientists who made important contributions to understanding radioactivity SWABT to explain the meaning of half-life. Student will be asked to find any sources of Radioactivity in his/her environment Slide 4 Science Park HS -- Honors Chemistry Early Pioneers in Radioactivity Roentgen: Discoverer of X-rays 1895 Becquerel: Discoverer of Radioactivity 1896 The Curies: Discoverers of Radium and Polonium 1900- 1908 Rutherford: Discoverer Alpha and Beta rays 1897 Slide 5 Science Park HS -- Honors Chemistry What do we mean by Radioactivity? Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. There are numerous types of radioactive decay. The general idea: An unstable nucleus releases energy to become more stable Slide 6 Science Park HS -- Honors Chemistry Some Key Definitions Before We Move on Z = The Atomic Number. Its the Number of Protons in the nucleus of an Atom. Nucleus: Its 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. Slide 7 Science Park HS -- Honors Chemistry The Nuclear Stability Belt Slide 8 Science Park HS -- Honors Chemistry Kinds of Radioactivity The three main decays are Alpha, Beta and Gamma Slide 9 Science Park HS -- Honors Chemistry Three Common Types of Radioactive Emissions Alpha Beta Gamma Slide 10 An alpha particle is identical to that of a helium nucleus. It contains two protons and two neutrons. Alpha Decay Slide 11 X A Z Y A - 4 Z - 2 + He 4 2 Alpha Decay unstable atom more stable atom alpha particle Slide 12 Alpha Decay Ra 226 88 Rn 222 86 He 4 2 Slide 13 X A Z Y A - 4 Z - 2 + He 4 2 Ra 226 88 Rn 222 86 + He 4 2 Alpha Decay Slide 14 Rn 222 86 He 4 2 + Po 218 84 He 4 2 Rn 222 86 + Y A Z He 4 2 Alpha Decay Slide 15 He 4 2 U 234 92 + Th 230 90 He 4 2 X A Z + Th 230 90 He 4 2 Alpha Decay Slide 16 Th 230 90 + Y A Z He 4 2 Alpha Decay He 4 2 + Ra 226 88 He 4 2 Th 230 90 Slide 17 X A Z + Pb 214 82 He 4 2 Alpha Decay He 4 2 + Pb 214 82 He 4 2 Po 218 84 Slide 18 Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton and an electron. Slide 19 Beta Decay As a result of beta decay, the nucleus has one less neutron, but one extra proton. The atomic number, Z, increases by 1 and the mass number, A, stays the same. Slide 20 Beta Decay Po 218 84 0 At 218 85 Slide 21 X A Z Y A Z + 1 + 0 Beta Decay Po 218 84 Rn 218 85 + 0 Slide 22 Th 234 90 Y A Z + 0 Beta Decay Th 234 90 Pa 234 91 + 0 Slide 23 X A Z Pb 210 82 + 0 Beta Decay Tl 210 81 Pb 210 82 + 0 Slide 24 Bi 210 83 Y A Z + 0 Beta Decay Bi 210 83 Po 210 84 + 0 Slide 25 X A Z Bi 214 83 + 0 Beta Decay Pb 214 82 Bi 214 83 + 0 Slide 26 Science Park HS -- Honors Chemistry 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. Slide 27 Science Park HS -- Honors Chemistry Another Contribution from Rutherford: Half-life of Radioactive Atoms The half-life of a radioactive substance, is the time required for one half of it to decay. Slide 28 Science Park HS -- Honors Chemistry Sources of Radioactivity Primordial - from before the creation of the Earth Cosmogenic - formed as a result of cosmic ray interactions Human produced - enhanced or formed due to human actions (minor amounts compared to natural) Slide 29 Science Park HS -- Honors Chemistry 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 Slide 30 Science Park HS -- Honors Chemistry Radioactivity Is it a Health Problem? The Alpha, Beta and Gamma particles all add energy to the bodys 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 Slide 31 Science Park HS -- Honors Chemistry Radiation Exposure to Americans Slide 32 Science Park HS -- Honors Chemistry Summary/Questions Name three of the science pioneers in the study of Radioactivity.? 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? Slide 33 Science Park HS -- Honors Chemistry Where to Get More Information http://www.physics.isu.edu/radinf/natural. htm EPA (Environmental Protection Agency) Dept of Energy

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