2.
Radioactive Dating
Finding the age of an object based on
the amount of radioactive isotopes in it.
Example:
Carbon-14 has a half life of 5715 years.
Carbon-12 & Carbon-14 amounts remain
constant while an object is living.
When an organic artifact is found the
Carbon-14 can be compared to the
Carbon-12.
4.
Half-Life
The amount of time it takes for ½ of an
unstable element to decay.
5.
Half-Life
The amount of time it takes for ½ of an
unstable element to decay.
Example: carbon-14 half life is 5715. If a
80mg sample decays over 22860 years, how
much will remain?
6.
Half-Life
The amount of time it takes for ½ of an
unstable element to decay.
Example: carbon-14 half life is 5715. If a
80mg sample decays over 22860 years, how
much will remain?
22860/5715 = 4 half lives.
7.
Half-Life
The amount of time it takes for ½ of an
unstable element to decay.
Example: carbon-14 half life is 5715. If a
80mg sample decays over 22860 years, how
much will remain?
22860/5715 = 4 half lives.
80/2=40mg 1st half life
8.
Half-Life
The amount of time it takes for ½ of an
unstable element to decay.
Example: carbon-14 half life is 5715. If a
80mg sample decays over 22860 years, how
much will remain?
22860/5715 = 4 half lives.
80/2=40mg 1st half life
40/2=20mg 2nd half-life
9.
Half-Life
The amount of time it takes for ½ of an
unstable element to decay.
Example: carbon-14 half life is 5715. If a
80mg sample decays over 22860 years, how
much will remain?
22860/5715 = 4 half lives.
80/2=40mg 1st half life
40/2=20mg 2nd half-life
20/2=10mg 3rd half-life
10.
Half-Life
The amount of time it takes for ½ of an
unstable element to decay.
Example: carbon-14 half life is 5715. If a
80mg sample decays over 22860 years, how
much will remain?
22860/5715 = 4 half lives.
80/2=40mg 1st half life
40/2=20mg 2nd half-life
20/2=10mg 3rd half-life
10/2=5mg 4th half-life
12.
Radioactive Dating
An object was found with 1/8 the ratio of
carbon-14 to carbon-12. How old is it? (one
half-life = 5715 years)
13.
Radioactive Dating
An object was found with 1/8 the ratio of
carbon-14 to carbon-12. How old is it? (one
half-life = 5715 years)
14.
Radioactive Dating
An object was found with 1/8 the ratio of
carbon-14 to carbon-12. How old is it? (one
half-life = 5715 years)
1 divided by 2 = ½ 1st half-life
15.
Radioactive Dating
An object was found with 1/8 the ratio of
carbon-14 to carbon-12. How old is it? (one
half-life = 5715 years)
1 divided by 2 = ½ 1st half-life
½ divided by 2 = ¼ 2nd half-life
16.
Radioactive Dating
An object was found with 1/8 the ratio of
carbon-14 to carbon-12. How old is it? (one
half-life = 5715 years)
1 divided by 2 = ½ 1st half-life
½ divided by 2 = ¼ 2nd half-life
¼ divided by 2 = 1/8 3rd half-life
17.
Radioactive Dating
An object was found with 1/8 the ratio of
carbon-14 to carbon-12. How old is it? (one
half-life = 5715 years)
1 divided by 2 = ½ 1st half-life
½ divided by 2 = ¼ 2nd half-life
¼ divided by 2 = 1/8 3rd half-life
18.
Radioactive Dating
An object was found with 1/8 the ratio of
carbon-14 to carbon-12. How old is it? (one
half-life = 5715 years)
1 divided by 2 = ½ 1st half-life
½ divided by 2 = ¼ 2nd half-life
¼ divided by 2 = 1/8 3rd half-life
3 x 5715 = 17145 years
20.
½ Life Example
A rock has 4.3mg of Potassium-40. The
rock was dated 3.84 billion years old.
How much Potassium-40 was originally
present? (1 half-life = 1.28 billion years)
21.
½ Life Example
A rock has 4.3mg of Potassium-40. The
rock was dated 3.84 billion years old.
How much Potassium-40 was originally
present? (1 half-life = 1.28 billion years)
3.84/1.28 = 3 half lives
22.
½ Life Example
A rock has 4.3mg of Potassium-40. The
rock was dated 3.84 billion years old.
How much Potassium-40 was originally
present? (1 half-life = 1.28 billion years)
3.84/1.28 = 3 half lives
4.3 x 2 = 8.6 1st half-life
23.
½ Life Example
A rock has 4.3mg of Potassium-40. The
rock was dated 3.84 billion years old.
How much Potassium-40 was originally
present? (1 half-life = 1.28 billion years)
3.84/1.28 = 3 half lives
4.3 x 2 = 8.6 1st half-life
8.6 x 2 = 17.2 2nd half-life
24.
½ Life Example
A rock has 4.3mg of Potassium-40. The
rock was dated 3.84 billion years old.
How much Potassium-40 was originally
present? (1 half-life = 1.28 billion years)
3.84/1.28 = 3 half lives
4.3 x 2 = 8.6 1st half-life
8.6 x 2 = 17.2 2nd half-life
17.2 x 2 = 34.4 3rd half-life
25.
½ Life Example
A rock has 4.3mg of Potassium-40. The
rock was dated 3.84 billion years old.
How much Potassium-40 was originally
present? (1 half-life = 1.28 billion years)
3.84/1.28 = 3 half lives
4.3 x 2 = 8.6 1st half-life
8.6 x 2 = 17.2 2nd half-life
17.2 x 2 = 34.4 3rd half-life
Answer = 34.4mg
26.
Uses of Nuclear Chemistry
Smoke detectors: use Americium-241
Art forgeries: found through neutron
activation analysis.
Medical: to diagnose and treat disease.
X-rays
Thallium-201 intravenously
PET scans
27.
Radiation Exposure
rem: the unit used to express biological
effects of radiation.
0-25 no effect
25-50 slight decrease in white cell count
50-100 marked decrease in white cell count
100-200 nausea and hair loss
200-500 internal bleeding
500+ death
29.
A New Approach
All half life problems have 5 parts
1)Length of decay length of decay
# of half lives =
2)Length of half life
length of half life
3)Initial amount Divide by 2 if finding final amount.
Multiply by 2 if finding original amount.
4)Final amount
5)Number of half lives
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