Unit 10 Lec 2
 Strong nuclear force (binding force)
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Name:_____________________________Period:____
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- Sometimes this is too weak!

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Sodium usually has a mass of:_____________
In this example this isotope has a mass of _________
and is _____________.
Therefore it _____________ to _________ through
_____________________
Unstable Nuclei - Decay
• Nuclear Decay = Atoms __________ _________________ to attain a better neutron-proton ratio.
• The half-life of a radioisotope is _______________ and independent of the sample ______________.
• Half-life: ____________________________________________________________________________
•
Half lives can be as long as millions of years and as short as nanoseconds
Half-Life of several isotopes:
Example 1: Barium-122 has a half-life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10
minutes to set up an experiment using barium-122, how much barium-122 will be left when the experiment begins?
Time
start
2 min
4 min
6 min
8 min
10 min
mass
Example 2: If 10 mg of iodine 131 is given to a patient, how much is left after 24 days? The half-life of iodine-131 is 8
days.
Time
start
8 days
16 days
24 days
mass
Example 3: Iodine-131 is used to destroy thyroid tissue in the treatment of an overactive thyroid. The half-life of
iodine-131 is 8 days. If a hospital receives a shipment of 200 g of iodine-131, how much I-131 would remain after 32
days?
Time
Start
8 days
16 days
24 days
32 days
mass
Example 4: The half-life of carbon-14 is 5730 years. A piece of linen found today contains carbon-14 and gives an
activity of 15 counts per minute per gram of carbon. If an anthropologist found an ancient piece of linen believed to
date back to the Neolithic period which gave only 7.5 counts per minute per gram of carbon, how old is the ancient
linen ?
Example 5: Technetium-99m is used for brain scans. If a laboratory receives a shipment of 200 g of this isotope and
after 24 hours only 12.5 g of this isotope remain, what is the half-life of technetium-99m? To do this, you can start
from either end. If you start from left, input the beginning mass. Then you will decrease by half. For the time, you
should start from the right and subtract half of the time shown.
Time
mass
start
24 hrs
12.5