Transcript Beta Emissions

Beta Emissions
(Principles of Carbon Dating)
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Radioactive Emissions (Radiation)
Radiation - Energy emitted in the form of
waves (light) or particles (photons).
Beta Radiation: emits a beta particle (an
electron). In beta decay a neutron in the
nucleus changes into a proton, an electron and a
neutrino and ejects the high speed electron
(beta particle) from the nucleus..
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Radioactive Emissions (Radiation)
Type
Description
Equivalent
Alpha
Dense (+)
charged
particle
(-) charged
particle
Helium
nucleus
Beta
Gamma Type of
energy
High
speed
electron
High
energy
photons
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Symbol
Penetrating
Power
He
Stopped by
thick paper
4
2
()
0
-1
e
0
b
-1
0
0
g
Stopped by
6mm of Al
Stopped by
several cm
of Pb
Penetrating Power of Radioactive Emissions
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Beta Decay
When a parent nucleus decays by the Beta (β)
decay process, an electron, called a beta particle
(β) is emitted. The resulting daughter nucleus
will always have the same atomic mass and an
atomic number increased by one.
atomic weight is constant
63
28
Ni 
63
29 Cu

0
1e
emitted beta
particle
atomic number
increases
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Beta Decay
A beta particle is created in the nucleus by a
process in which one neutron is transformed into a
proton and an electron.
n p e
1
0
1
1
0
1
Example of Beta Decay:
14
14
0
6 C  7 N  -1e
Mass: 14 = 14 + 0
14 = 14
Charge: 6 = 7 + (-1)
6 =6
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Beta Decay Application – Carbon Dating
Click here for a short
video on carbon dating
dead biological materials.
How old are
these bones?
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Beta Decay Application – Carbon Dating
Carbon dating is a method of determining the age of
dead biological materials based on the rate of decay of
the radioactive isotope Carbon-14.
• Willard F. Libby pioneered carbon dating at the
University of Chicago in the 1950's.
• In 1960, he won the Nobel Prize for Chemistry for
this work.
• Radiocarbon dating is now the most widely used
method of age estimation in the field of archaeology.
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Beta Decay Application – Carbon Dating
Carbon-14 is an unstable isotope of Carbon-12.
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Beta Decay Application – Carbon Dating
Carbon-14 begins when high-energy cosmic rays enter
the earth's atmosphere. The rays collide with atoms to
create a secondary cosmic rays in the form of an
energetic neutron. (Every person on the earth is hit with
about 500,000 cosmic rays every hour.)
neutron
cosmic ray
atom
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Beta Decay Application – Carbon Dating
These neutrons can then collide with the diatomic nitrogen
molecules in the atmosphere. These collisions produce
carbon-14 and nitrogen atoms, as well as protons.
neutron
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Beta Decay Application – Carbon Dating
Just like carbon-12, carbon-14 chemically reacts with the
oxygen in the atmosphere to produce carbon dioxide.
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Beta Decay Application – Carbon Dating
Almost all of the carbon dioxide in our atmosphere is
derived from non-radioactive carbon-12 atoms. The ratio
of normal carbon-12 to carbon-14 in the air and in all living
things is nearly constant at any given time. This ratio is
approximately 1 in every in one trillion carbon atoms is
carbon-14.
1 Carbon-14

1,000,000,000,000 Carbon-12
14
6C
12
6C
 1.0 x10
13
12
Beta Decay Application – Carbon Dating
Like carbon dioxide made from xarbon-12, carbon dioxide
made from carbon-14 enters the carbon cycle through
photosynthesis.
As animals eat plant life they assimilate both carbon-12
and carbon-14 into their bodies in the ratio that carbon-12
and carbon-14 exist in nature.
The process of live
organisms (including
humans) taking in
carbon continues until
death.
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Beta Decay Application – Carbon Dating
Once an organism dies, it stops consuming Carbon and the
amount of carbon-12 in the tissue remains constant.
But, the carbon-14 that was in the tissue radioactively
decay (with a haf-life of 5,730 years) into nitrogen-14.
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Beta Decay Application – Carbon Dating
By measuring the ratio of c-12 to c-14 in a sample and
comparing it to the ratio in a living organism, it is possible
to determine the age of a formerly living thing.
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Beta Decay Application – Carbon Dating
The formula to calculate how old a sample is by
carbon-14 dating is:
t = [ln(Nf/No)/(-0.693)]x t1/2
ln(
Nf
)
N o 1/ 2
t
t
0.0693
where:
ln is the natural logarithm
Nf/No is the percent of carbon-14 in the sample
compared to the amount in living tissue
t1/2 is the half-life of carbon-14 (5,730 years)
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