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Introduction to Physical Science: Atoms, Radioactivity, and Ages

Learn about atoms, radioactivity, and ages in physical science, including topics such as the structure of atoms, radiation dosage, radioactive dating, and isotopic values determination. Engage with key concepts in understanding the age of the solar system and the universe.

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Introduction to Physical Science: Atoms, Radioactivity, and Ages

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  1. Introduction to Physical ScienceMonday, Wednesday, ThursdayTom Burbinetomburbine@astro.umass.edu

  2. Atoms • Atoms are made up of 3 types of particles • Protons – positive charge (+1) • Electrons – negative charge (-1) • Neutrons – neutral charge (no charge) • Protons and Neutrons are found in the nucleus

  3. Strong Nuclear Force • Keeps protons and neutrons together in the nucleus

  4. Radioactivity • Radioactivity – decay of an atomic nucleus • All elements with an atomic number greater than 82 (lead) are radioactive

  5. How old is the solar system?

  6. How old is the solar system? • ~4.6 billion years • All meteorites tend to have these ages • Except:

  7. How old is the solar system? • ~4.6 billion years • All meteorites tend to have these ages • Except: • Martian meteorites • Lunar meteorites

  8. How old is the universe?

  9. How old is the universe? • ~13.7 billion years (±200 million years)

  10. Radiation dosage • 1 rad = 0.01 J of radiant energy absorbed by kilogram of tissue • Rem = rads x Q where Q is a quality factor which attempts to convert rads from different types of radioactivity into a common scale of biological damage.

  11. Radon is a naturally occurring radioactive gas

  12. Ages • Ages

  13. How do you determine this age?

  14. Radioactivity • The spontaneous emission of radiation (light and/or particles) from the nucleus of an atom

  15. Some types of radiation • Alpha particle – 2 protons and 2 neutrons (Helium nucleus) • Do not normally penetrate clothing • High kinetic energy (due to high mass) ; can damage living tissue • Beta particle – electron (from a neutron when it becomes a proton) • Penetrate clothing and into skin • Gamma ray - High-frequency radiation • Penetrate into skin and can damage molecules in cells

  16. http://www.darvill.clara.net/nucrad/types.htm

  17. Radioactivity http://wps.prenhall.com/wps/media/tmp/labeling/2130796_dyn.jpg

  18. Half-Life • The time required for half of a given sample of a radioactive isotope (parent) to decay to its daughter isotope.

  19. Radioactive Dating • You are dating when a rock crystallized http://faculty.weber.edu/bdattilo/images/tim_rock.gif

  20. Radioactive Dating n =no(1/2)(t/half-life) no = original amount n = amount left after decay

  21. Exponential decay is where the rate of decay is directly proportional to the amount present. http://www.gpc.edu/~pgore/myart/radgraph.gif

  22. Remember • Number of original atoms (parent atoms) • = number of daughter atoms today + number of parent atoms today

  23. http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/graphics/radio1.gifhttp://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/graphics/radio1.gif

  24. What are the assumptions to get an age?

  25. What are the assumptions? • No loss of parent atoms • Loss will increase the apparent age of the sample. • No loss of daughter atoms • Loss will decrease the apparent age of the sample. • No addition of daughter atoms or if daughter atoms was present when the sample formed • If there was, the age of the sample will be inflated • These can possibly be all corrected for

  26. Commonly Used Long-Lived Isotopes in Geochronology

  27. How do you determine isotopic values?

  28. How do you determine isotopic values? • Mass Spectrometer

  29. It is easier • To determine ratios of isotopic values than actual abundances

  30. Carbon-14 • 99% of the carbon is Carbon-12 • 1% is Carbon-13 • 0.0000000001% is Carbon-14 • The half-life of carbon-14 is 5730±40 years. • It decays into nitrogen-14 through beta-decay (electron and an anti-neutrino are emitted).

  31. Due to Carbon-14’s short half-life, can only date objects up to 60,000 years old

  32. Plants take up atmospheric carbon through photosynthesis http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html

  33. When something dies, it stops being equilibrium with the atmosphere http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html

  34. Why is Carbon-14 still present if it has such a short half-life?

  35. Why is Carbon-14 still present if it has such a short half-life? • Cosmic rays impact Nitrogen-14 and create Carbon-14 • Cosmic rays are energetic particles (90% are protons) originating from space. From the Sun (solar cosmic rays) or outside the solar system (galactic cosmic rays) • n + 14N → 14C + p

  36. http://en.wikipedia.org/wiki/Image:Radiocarbon_bomb_spike.svghttp://en.wikipedia.org/wiki/Image:Radiocarbon_bomb_spike.svg

  37. Any Questions?

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