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Atoms

Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine tomburbine@astro.umass.edu. Atoms. Atoms are made up of 3 types of particles Protons – positive charge (+1) Electrons – negative charge (-1) Neutrons – neutral charge (no charge)

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Atoms

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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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