Transcript Radioactivity

Radioactivity
Decay Constant
Activity
Exponential decay
By Hannah I. Terhorst
Decay Constant
λ = decay constant
The decay constant λ of the radio-nuclide is the probability
that an individual nucleus will decay within a unit of time.
Exp.
0.2 s-1 = every nucleus has a 0.2 chance of decaying in one second
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Activity
The activity A of a source is the number of its nuclei that
decay in unit time.
Unit: 1 becquerel (Bq) is an activity of 1 decay per
second
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Exponential decay
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the number of nuclei in a sample always decreases
in the same way
t ½ = half time
It is the time taken for half the radioactive nuclei to decay.
different half-lives vary widely  from seconds to
millions of years
 Exponential decay curve
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3
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The higher the probability of decay λ
 the more rapidly nuclide decay
 the shorter is half-life
4
The age of rocks
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Measuring how many 238U changed to 206Pb
Uranium-238 has a very long half-life of 4500
million years  stable nuclide lead-206
Other nuclides in the decay chain can be
ignored
5
Carbon dating
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Carbon-14 (14C) half-life of 5730 years
All living things take 14C more usual 12C
(photosynthesis)
14C slowly decays  percentage slowly
decreases
Used to date bones, wood, paper, cloths
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Exp. Egyptian mummy
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Step 1
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Step 2
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Source
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Book page 342, 343, 345