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Half-life.
What is Half-life?
1. Half-life is the time taken for half of the radioactive nuclei to decay.
2. Half-life is the time
taken
for the count rate to fall to half of its
original reading.
There are a number of ways to
define half-life.
Remember
one of the above definitions, it may be useful in the exams.
An Explanation of Half-life.
A radioactive material
will have some nuclei that are
stable
and some that are unstable.
The stable nuclei don't change,
that is what stable means. In the picture
below,
the unstable nuclei (shown as brown balls) will
change
into stable nuclei (shown as purple
balls) and emit radioactivity.
Half-life is a
measure of the time
taken for
the unstable nuclei to change into
stable nuclei.
Different substances do this at different rates.
Some do it very quickly and
half of the unstable nuclei
decay
in less than one second.
For example, lithium-8 has a half-life
of only 0·85 seconds.
Some do it very slowly and half of the
unstable nuclei take
billions
of years to decay.
For example, uranium-238 has a half-life
of 4·51 billion years.
Remember that half-life is an amount of time.
In the same amount of time, the picture on
the right above
will lose half of the remaining unstable
nuclei.
Continued on the next page.
Links
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Half-life
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