astr 1101-001 spring 2008
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ASTR 1101-001 Spring 2008. Joel E. Tohline, Alumni Professor 247 Nicholson Hall [Slides from Lecture25]. Chapter 8: Principal Topics. How old is the Solar System? - PowerPoint PPT PresentationTRANSCRIPT
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ASTR 1101-001Spring 2008
Joel E. Tohline, Alumni Professor
247 Nicholson Hall
[Slides from Lecture25]
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Chapter 8: Principal Topics
• How old is the Solar System?• Nebular Hypothesis + Planetesimals + Core
Accretion: A model that explains how the solar system acquired its key structural properties.– Directions and orientations of planetary orbits– Relative locations of terrestrial and Jovian planets– Size and compositions of planets
• Observational evidence for extrasolar planets
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How old is the Solar System?
• Radioactive dating
• First, let’s discuss the idea of radioactive isotopes of atomic elements
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How old is the Solar System?
• Radioactive dating
• First, let’s discuss the idea of (radioactive & non-radioactive) isotopes of atomic elements
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Chemical Elements & Their Isotopes
Courtesy of: http://atom.kaeri.re.kr/
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Chemical Elements & Their Isotopes
Hydrogen
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Chemical Elements & Their Isotopes
Hydrogen
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Chemical Elements & Their Isotopes
Helium
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Chemical Elements & Their Isotopes
Helium
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Chemical Elements & Their Isotopes
Carbon
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Chemical Elements & Their Isotopes
Carbon
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Chart of Nuclides
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Chart of Nuclides
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Chart of Nuclides
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Chart of Nuclides
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Chart of Nuclides
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Chart of Nuclides
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Chart of Nuclides
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Chart of Nuclides
C14
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Chart of Nuclides
C14
6 + 8 = 14
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How old is the Solar System?
• Radioactive dating• First, let’s discuss the idea of (radioactive & non-
radioactive) isotopes of atomic elements• Now let’s discuss radioactivity and the concept
of “half-life”– “The half-life of an isotope is the time interval in which
one-half of the nuclei decay.” [See Box 8-1 in the textbook.]
– http://www.colorado.edu/physics/2000/isotopes/radioactive_decay3.html
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Radioactive Decay
t1/2 = half-life
Courtesy of: www.splung.com/content/sid/5/page/radioactivity
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Color Indicates Approximate “Half-Life”
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Some more precise “Half-Life” values
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Some more precise “Half-Life” values
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Some more precise “Half-Life” values
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Decay of 14C to 14N
14C
14N
t1/2 = 5730 years
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Some more precise “Half-Life” values
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Decay of 87Rb to 87Sr
t1/2 = 47 billion years
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Some more precise “Half-Life” values
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Decay of 238U to 206Pb
t1/2 = 4.5 billion years
238U
206Pb
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Radioactive Decay• As the abundance of the radioactive isotope (for example,
14C) decreases steadily over time, the abundance of the final stable isotope (for example, 14N) steadily increases.
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14C Dating• Suppose an archeologist digs up a primitive weapon
made partly of wood and determines that the wood contains an isotopic abundance ratio 14N/14C = 3. How old is the weapon if we assume that, originally, the wood contained no 14N ?
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14C Dating14N
14C
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14C Dating14N
14C
At what time does the abundance ratio 14N/14C = 3 ?
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14C Dating14N
14C
At what time does the abundance ratio 14N/14C = 3 ?
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14C Dating14N
14C
At what time does the abundance ratio 14N/14C = 3 ?
Age of wood = 2 t1/2 = 2 x (5730 yrs) = 11,460 yrs
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14C Dating• Suppose an archeologist digs up a primitive weapon
made partly of wood and determines that the wood contains an isotopic abundance ratio 14N/14C = 3. How old is the weapon if we assume that, originally, the wood contained no 14N ?
• ANSWER: 11,460 years• In practice, the ‘dating’ technique is messier than this,
but this should give you a general idea of how the radioactive dating technique works.
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14C Dating• Suppose an archeologist digs up a primitive weapon
made partly of wood and determines that the wood contains an isotopic abundance ratio 14N/14C = 3. How old is the weapon if we assume that, originally, the wood contained no 14N ?
• ANSWER: 11,460 years• In practice, the ‘dating’ technique is messier than this,
but this should give you a general idea of how the radioactive dating technique works.
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238U Dating• Suppose an astronomer discovers a meteorite and
determines that the meteorite contains an isotopic abundance ratio 206Pb/238U = 1. How old is the meteorite if we assume that, when it originally formed, the meteorite contained no 206Pb ?
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Atomic Bombs
• Rely on spontaneous fission (radioactive decay) of heavy nuclei, such as Uranium and Plutonium
• A ‘critical mass’ of fissionable material will explode because the decay products from spontaneous fission strike nearby nuclei and induce those nuclei to fission runaway chain reaction
• First atomic bombs were constructed during World War II in the so-called ‘Manhattan Project’ centered at Los Alamos, NM
http://www.lanl.gov/history/