Write down the equation for the surface area of that sphere.
2.
On the surface of the sphere you’ve drawn, sketch an area representing a small
particle detector.
If the source emits radiation evenly in all directions, write an
equation for the fraction of its radiation that would pass through the particle
detector as a function of the area of the detector and the radius of the sphere.
3.
Now draw another even larger sphere still centered on the radioactive source. Draw
the same particle detector on the surface of the larger sphere.
Now write an
equation for the fraction of the source’s radiation that would pass through the
particle detector as a function of the area of the detector and the radius of the new
sphere.
Is the rate of particles passing through the detector when it is on the surface
of the larger sphere higher or lower than its rate when it is on the smaller sphere?
4.
Write an equation for the relationship of a detector's counting rate and its distance
from radioactive source.
Sketch a graph of this relationship. What assumptions does
this relationship require?
191
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
DISTANCE FROM SOURCE – 1202Lab8Prob1
P
REDICTION
Use geometry to calculate how the particle count rate varies with distance from a small
radioactive source. On what assumptions is your calculation based?
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
number of trials and the same calculation.
In which case is the measurement
uncertainty a smaller fraction of the measurement?
By approximately what factor did
the average measurement change when you increased the counting time by a factor of
4? What does this tell you about the time period necessary when taking data?
Keep
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '17
 Aaron Wynveen
 Physics

Click to edit the document details