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Radioisotopic Dating
Carbon14 Dating:
Of the stable
carbon on
earth, about 99% is C12 and 1% is C13. The
halflife of carbon14 is 5730 years.
Carbon14
is formed in the upper atmosphere by the
bombardment of ordinary nitrogen atoms by
neutrons from cosmic rays. See next slide
• Write the balanced equation for the formation
of C14
• Steady state of CO
2
created, plants take it in during
photosynthesis
• Shroud of Turin (claimed to be part of Christ’s burial shroud) was
shown to be less than 800 years old
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View Full Document In the upper atmosphere, a nitrogen14 nucleus absorbs a neutron. A carbon14 nucleus and another particle
are formed. What is the other particle?
EXAMPLE 4.2
5
More Nuclear Equations
In one reaction that might be a future energy source, a hydrogen2 nucleus combines with a hydrogen3
nucleus, forming a helium4 nucleus and another particle. What is the other particle formed?
Exercise 4.2
Solution
We start by writing the symbols for nitrogen14 and a neutron (from Table 4.4) on the left of an equation, and the
symbol for carbon14 on the right.
The total of nucleon numbers on the left is 15, and on the right is 14, so the missing particle must have a nucleon
number of 15  14 = 1. The total atomic number on the left is 7 and on the right is 6, so the missing particle must
have an atomic number of 1.
From Table 4.4, the particle with an atomic number of 1 and a nucleon number of
1 is a proton.
N +
n
→
C +
?
14
7
1
0
14
6
N +
n
→
C +
?
14
7
1
0
14
6
1
1
N +
n
→
C +
p
14
7
1
0
14
6
1
1
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View Full Document An old wooden implement has carbon14 activity oneeighth that of new wood. How old is the artifact? The
halflife of carbon14 is 5730 years.
EXAMPLE 4.5
5
Radioisotopic Dating
Solution
Using the relationship
we see that oneeigth is
, where
n
= 3; that is, the fraction
is
. The carbon14 has gone through three
halflives. The wood is therefore about 3
x
5730 = 17,190 years old.
Fraction remaining =
1
2
n
1
2
n
1
8
1
2
3
How old is a piece of a fur garment that has carbon14 activity
that of living tissue? The halflife of
carbon14 is 5730 years.
Exercise 4.5A
1
16
Strontium90 has a halflife of 28.5 years. How long will it take for the strontium90 now on Earth to be
reduced to
of its present amount?
Exercise 4.5B
1
32
Radioisotopic Dating
Tritium Dating:
Tritium is a radioactive
isotope of hydrogen.
It has a halflife of
12.26 years and can be used for dating
objects up to 100 years old.
• Has been used to check claims about age of certain
alcoholic beverages, such as brandies and vintage
wines!
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View Full Document • Homework is due today,
answers will be posted on
WebCT
•
Next Homework
assignment: Chapter 4:
#
5470 even
• Extra credit due today –
none will be accepted late
• Chemistry Nobel prize
2007 goes to Gerhard Ertl for
his studies of surface
chemistry 
see article #11
Chemical reactions catalyzed by a metal surface
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This note was uploaded on 04/23/2009 for the course CHEMISTRY CH105 taught by Professor Armstrong during the Fall '07 term at BC.
 Fall '07
 ARMSTRONG
 Chemistry, Atom, pH, HalfLife

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