Radioactive Decay and Radiometric Dating

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Radioactive Decay and Radiometric Dating Extra credit: chapter 7 in Bryson See online (link fixed) or moodle Radioactivity and radiometric dating Atomic nucleus Radioactivity Allows us to put

1 Radioactive Decay and Radiometric Dating Extra credit: chapter 7 in Bryson See online (link fixed) or moodle Radioactivity and radiometric dating Atomic nucleus Radioactivity Allows us to put numerical ages on geologic events Atomic structure Atom model Nucleus composed of protons and neutrons Orbiting the nucleus are electrons negative electrical charges Atomic number Identifying number Number of protons Determines the properties Mass number Protons + Neutrons Nucleons Not the same as Atomic Mass

Periodic Table Series in Periodic Table Isotope Same number of protons Different number of neutrons Different mass number than another isotope of the

small 0-5 to 0-4 m radius Strong interaction binds nucleons Protons repel one another Neutrons counteract this More neutrons than protons in larger

2 Periodic Table Series in Periodic Table Isotope Same number of protons Different number of neutrons Different mass number than another isotope of the same element Variant atom of the same element Say Gold 88 for Au-88 Radioactivity Spontaneous breaking apart (decay) of atomic nuclei Nucleus Very small 0-5 to 0-4 m radius Strong interaction binds nucleons Protons repel one another Neutrons counteract this More neutrons than protons in larger atoms Nuclear forces Very strong at small distances (0-5 m) Weakens at 0X that distance (0-4 m) Elements at. # 8 + are unstable, because they are big Radioactive

3 Radioactive decay Parent atom an unstable isotope Daughter products Formed from the decay of a parent atoms Different element because of nuclear changes Types of radioactive decay Alpha emission Beta emission α β Gamma radiation γ Alpha emission α Beta emission β N + P + Positive charge Large non-penetrating Negative charge electron N P + + e - Small, but low energy minor penetration Gamma radiation Penetrating, energetic photons Lower energy of excited daughter nucleus No charge, less mass than electron γ In the nucleus of an atom, the strong force is a relatively. short-range force.. long-range force. 3. unstable force. 4. neutralizing force. 5% 5% 5% 5% 3 4 3

4 The strong force acts between. All of thes choices.. Neutrons and electrons 3. Neutrons and protons 4. Nucleons in a nucleus 5. Protons and electrons. The radioactive decay of nature s elements occurs in the 0%. air we breathe.. all of these. 3. interior of Earth. 4. soil we walk on. 5. Sun, stars and space 0% 0% 0% 0% Of alpha, beta, and gamma radiation, two are high-speed particles, and the one that isn t is. all of these are different forms of electromagnetic waves, so none are particles.. alpha. 3. beta. 4. gamma. 5% 5% 5% 5% 3 4 When an element ejects an alpha particle, the mass number of the 7% 7% resulting element. increases by.. increases by. 3. increases by reduces by. 5. reduces by reduces by. 7% 7% 7% 7% 6 When an element ejects a beta particle, the atomic number of that element. reduces by.. increases by. 3. reduces by. 4. increases by. 5. reduces by 4. 7% 7% 7% 7% 7% 7% 6 Which of these is actually a high-speed electron?. All of these are high speed electrons.. Alpha. 3. Beta. 4. Gamma. 5. None of these 4

Which of these is the most penetrating in common materials?. All of these are equally penetrating.. Alpha. 3. Beta. 4. Gamma. 5. None of these are penetrating.

5 Which of these is the most penetrating in common materials?. All of these are equally penetrating.. Alpha. 3. Beta. 4. Gamma. 5. None of these are penetrating. Nuclear Decay Equation Alpha Decay Ra-6 Rn-+α Total nucleons stays same, but on daughter (product) side Alpha decay α removes N o and P + Nuclear Decay Equation Beta Decay H-3 He-3 + β Total nucleons stays same Beta decay β N o P + + e - Balancing Nuclear Equations P + (protons) + e - (electrons) = N o (neutrons) Keep track of protons: elemental symbol α decay decreases by two by releasing them with two neutrons so atomic number goes down by, atomic mass goes down by 4 β decay increases protons by releasing electron so atomic number goes up by, atomic mass stays the same Decay of U-38 NAMES-- Pa: protactinium Th: thorium Ra: radium Rn: radon Po: polonium At: astatine Pb: lead Bi: bismuth Tl: thallium When thorium-34 emits a beta particle, it transforms to. paladium-34. platinum protactinium protactinium thorium*

When uranium-38 emits an alpha particle, uranium transforms to. neptunium-38. thorium-4. 3. thorium-38. 4. thorium-34. 5.

6 When uranium-38 emits an alpha particle, uranium transforms to. neptunium-38. thorium thorium thorium uranium*-38 Measuring Radioactivity Radioactive decay strips electrons from atoms Ions created Geiger counter--charged wire, results in clicks of counter Others rely on visual reactions of ions Half Life Parent to daughter ratios of H-3 Decay is random for any radioactive atom BUT: Predictable for mass of material One half of unstable parent material daughter product: HALF LIFE: L / Decay rate constant, unaffected by external conditions Half Life equation Amount remaining can be calculated by R = I n R remaining I initial n number of half-lives Calculate amount from half-life R = I n Start with 400 mg of Co-60 Half life is 5.5 years How much is left after 5.75 years? To use equation at right, First calculate how many half lives 3 half-lives yr yr halflife 5.75 years = = 5.75 years = halflife 5.5 yr 6

7 Calculate amount from half-life 400 mg of Co-60 Half life is 5.5 years How much is left after 3 half-lives? Calculate amount R = mg ( 400 ) = 50mg 3 7

Radioactive Decay and Radiometric Dating

Radioactive Decay and Radiometric Dating Radioactivity and radiometric dating Atomic structure Radioactivity Allows us to put numerical ages on geologic events Atomic structure reviewed Atom model Nucleus