PowerPoint Presentation Gems 160, April 24, 2002

1
GEMS 160 4/24/02

• Chemistry news
• Today Dale Kling, Jason Dunn
• Friday No more presentations, but certainly
  there will be more chemistry in the news
• Ch. 5, time, detection and risk
• Extra credit homework for Ch. 4 and 5
• Posted on discussion board
• 5 towards total homework points
• Due day of final exam
• Portfolio extra credit
• Two weeks will be evaluated, due by final exam
• Previous guidelines
• Current selections, 3 per week
• Highlight chem and environment aspects
• A paragraph on your response to the issues

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C-14 and the age of organic items

• C-14 is continually created in the atmosphere,
  U-238 is not
• N-14 is bombarded by cosmic neutrons, one of the
  two products is C-14. Write the equation.

• C-14 becomes part of atmospheric CO2
• CO2 becomes part of plants by photosynthesis
• As long as the plant is living CO2 is used
  andC-14 becomes part of the plant structure

3
C-14 and dead plants

• When the plant dies (is made into cloth or
  furniture) no new C-14 appears, but the nuclear
  decay continues by loss of ?. Write this
  equation. Only one product in addition to ?.

• Since C-14 in the atmosphere is constant, compare
  C-14 that would be found in a current sample to
  C-14 in the sample under study. of C-14
  remaining gives the age of the sample.
• A sample of the Shroud of Turin is found to have
  52 counts of radioactivity. A modern sample of
  comparable material and size has 60 counts. Is
  the Shroud old enough to be the burial cloth of
  Christ?
• 52/60 gt 87 remains, approx 0.14 half-life x
  5730 800 yrs

4
Detecting Radiation . Back to the beginning

• Property of ions ??
• Nuclear decay produces ionizing radiation !
• Have a detector that can measure electric current
  caused by ionized gas.
• Similar in principle to measuring the presence of
  ions in solution.
• Scintillation counter
• Special compound that fluoresces when it
  interacts with radiation.
• Count the flashes of light to get a measure of
  radioactivity
• Film badge
• Film becomes exposed in the presence of radiation
• The greater the exposure to radiation the darker
  the film
• Measures cumulative exposure over a period of
  time

5
Radiation exposure

• Background vs. anthropogenic
• Benefit vs. risk
• Greatest risk is from natural sources
• Radon gas, part of U-238 decay scheme
• ? rays from cosmic radiation
• K-40 in our bodies
• 0.01 of the 200 g in an average adult

6

• Pick the 3 items which will most greatly increase
  risk of death.
• 1. Smoke 2 cigarettes.
• 2. Spend 3 hours in a coal mine.
• 3. Drink Miami tap water for 1 year.
• 4. Ride a bicycle for 10 miles.
• 5. Climb rocks for 2 minutes.
• 6. Travel by jet for 1000 miles.
• 7. Live 1.5 months in a stone building.
• 8. Eat 40 tablespoons of peanut butter.
• Drink 30 12-oz. cans of diet drink with
  saccharin.
• 10. Have 1 chest X-ray.
• 11. Live 60 days with a cigarette smoker.
• 12. Drive a car for 300 miles.
• 13. Live 20 years near a poly(vinyl chloride)
  plant.
• 14. Live 150 years within 20 miles of a properly
  operating nuclear power plant.
• 15. Eat 100 charcoal broiled steaks.

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And the greatest risk is

• Each activity in the previous list increases the
  risk of death by 1 chance in a million.

For Friday

• Preview/review for final exam
• Course evaluations