Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine [e-mail]

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Introduction to Physical ScienceMonday,
Wednesday, ThursdayTom Burbinetomburbine_at_astr
o.umass.edu
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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

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Strong Nuclear Force

• Keeps protons and neutrons together in the nucleus

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Radioactivity

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

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How old is the solar system?
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How old is the solar system?

• 4.6 billion years
• All meteorites tend to have these ages
• Except

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How old is the solar system?

• 4.6 billion years
• All meteorites tend to have these ages
• Except
• Martian meteorites
• Lunar meteorites

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How old is the universe?
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How old is the universe?

• 13.7 billion years (200 million years)

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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.

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• Radon is a naturally occurring
  radioactive gas

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Ages

• Ages

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How do you determine this age?
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Radioactivity

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

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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

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• http//www.darvill.clara.net/nucrad/types.htm

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Radioactivity
http//wps.prenhall.com/wps/media/tmp/labeling/213
0796_dyn.jpg
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Half-Life

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

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Radioactive Dating

• You are dating when a rock crystallized

http//faculty.weber.edu/bdattilo/images/tim_rock.
gif
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Radioactive Dating

• n no(1/2)(t/half-life)
• no original amount
• n amount left after decay

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

• Number of original atoms (parent atoms)
• number of daughter atoms today number of
  parent atoms today

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http//academic.brooklyn.cuny.edu/geology/leveson/
core/topics/time/graphics/radio1.gif
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What are the assumptions to get an age?
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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

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Radioactive Parent (P) Radiogenic Daughter (D) Stable Reference (S) Half-life, t½ (109 y)  Decay constant, l (y-1)
40K 40Ar  36Ar 1.25 0.58x10-10
87Rb 87Sr 86Sr 48.8 1.42x10-11
147Sm 143Nd 144Nd 106 6.54x10-12
232Th 208Pb 204Pb 14.01 4.95x10-11
235U 207Pb 204Pb 0.704 9.85x10-10
238U 206Pb 204Pb 4.468 1.55x10-10
Commonly Used Long-Lived Isotopes in
Geochronology
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How do you determine isotopic values?
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How do you determine isotopic values?

• Mass Spectrometer

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It is easier

• To determine ratios of isotopic values than
  actual abundances

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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 573040 years.
• It decays into nitrogen-14 through beta-decay
  (electron and an anti-neutrino are emitted).

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

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• Plants take up atmospheric carbon through
  photosynthesis

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

http//hyperphysics.phy-astr.gsu.edu/hbase/nuclear
/cardat.html
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Why is Carbon-14 still present if it has such a
short half-life?
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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

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• http//en.wikipedia.org/wiki/ImageRadiocarbon_bom
  b_spike.svg

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Any Questions?