1. Radiochemical Dating
Chp 24

2. Iceman
Austria/Italy Border
dated: BCE
Horse Cave Painting
France
13000 BCE

3. Carbon Dating-to age once living artifacts.
Constantly forming C-14 mixes with stable C-12 and C-13 in Earth's biosphere.
Plants take in carbon atoms in photosynthesis and animals eat the plants.
The ratio of C-14, C-12, and C-13 remains constant as long as organism is alive.
After death, no more carbon is ingested and the C-14 starts to decay. C-14 has a half life of 5730 years.
The ratio of unstable C-14 to stable C-12 and C-13 decreases. Scientists measure this ratio and compare it to the constant atmospheric ratio to determine the object's age.
C-14 dating is limited to dating objects up to about 45,000 years.

4. Example 2 pg 872-Calculating the Amount of Remaining Isotope
Krypton-85 is used in indicator lights of appliances.The half-life of Krypton-85 is 11y. How much of a 2.00mg sample remains after 33 years?

5. Example 2 pg 872-Calculating the Amount of Remaining Isotope
Krypton-85 is used in indicator lights of appliances.The half-life of Krypton-85 is 11y. How much of a 2.00mg sample remains after 33 years?
33 yrs = 3 half lives
11 yrs
3 halfs lives = ½ x ½ x ½ = 1/8
1/8 x 2.00 mg = mg

6. The half life of cobalt-5 is 270 days. How much of a 5
The half life of cobalt-5 is 270 days. How much of a mg sample will remain after 810 days?

7. The half life of cobalt-5 is 270 days. How much of a 5
The half life of cobalt-5 is 270 days. How much of a mg sample will remain after 810 days?
810 days = 3 half lives
270 days
3 half lives = 1/8
1/8 x mg = mg

8. 9. Bandages can be sterilized by exposure to gamma radiation from cobalt-60 which has a half-life of 5.27 y. How much of a 10.0 mg sample of cobalt-60 is left after 1 half life? Two half lives? Three?
½ x mg = 5.00 mg
¼ x mg = mg
1/8 x mg = 1.25 mg

9. 10. If the passing of 5 half lives leaves 25 mg of a strontium-90 sample, how much was present in the beginning?

10. 10. If the passing of 5 half lives leaves 25 mg of a strontium-90 sample, how much was present in the beginning?
½ x ½ x ½ x ½ x ½ = 1/32
32 x 25 mg = 800 mg