Make a graph of the number of surviving
particles versus the number of sheets of material.
Since each sheet is a specific
thickness of material, you now have a graph of how the surviving amount of
radiation depends on the thickness of material. Try to guess what functions could
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SHIELD THICKNESS – 1202Lab8Prob3
represent this graph.
Check your guesses by graphing them to see if they match
your points.
4.
Imagine that all of the sheets of material are very thin and are pushed together to
make one thick piece of material.
As the particles pass through a thin sheet, the
number entering the next sheet is reduced.
On what quantity(ies) does this change
in the number of particles depend?
Write an equation for the change of the number
of radiation particles per small amount of thickness (dN/dT).
Solve this equation
for the surviving number of particles as a function of material thickness.
Check to
see if this function matches your graph in question 3.
5.
Compare the mathematics for your hypothetical description of the shielding of
radioactive particles by material to that of radioactive decay described in your
textbook.
How are they similar?
Different?
P
REDICTION
Write down a mathematical function that describes the effect of material thickness on
the intensity of radiation that passes through that material. Describe the reasoning that
leads you to that function.
E
XPLORATION
WARNING:
The radioactive sources available for this problem provide low
intensity radiation, and are safe if handled with respect for short amounts of
time. Do not remove them from the laboratory, and do not attempt to open the
plastic disks containing the sources.
If a disk breaks open inform your TA
immediately, do not touch it.
Make sure you read the Equipment and Software appendices to understand the
operation of the Geiger counter before trying to operate it.
Place a radioactive source
near the detector, turn on the counter. Try the controls, and make sure every group
member understands how to operate it.
Try each of your sources to make sure the
equipment is functioning
.
With the detector working you now need to determine how to make your measurement
uncertainty as small a practical.
Start by using the detector to measure the number of
counts from a radioactive source in some short time interval, say 10 or 15 seconds.
Repeat this measurement several times, recording the number of counts occurring in
each fixed time interval. Compute the average number of counts per second and the
difference of each trial from that average.
Calculate the average of these differences for
all of your trials.
That average difference represents your counting uncertainty for the
measurement.
Now increase your time interval by a factor of 4 and repeat the same
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