Name
Date
Using a GM Radiation Monitor
In this investigation, you will be working with a digital radiation
monitor that contains a GM tube. You will explore how this
monitor works by measuring some of the ionizing radiation in
your classroom. This monitor detects ,  and  radiation.


The thin mica window at the front of the monitor
window is fragile! Please do not let anything (especially a
pointed object) touch the window.
Watch your teacher’s demonstration of how to set the
counter to count for 6 minutes using the timed count mode
and then set your counter to count for 6 minutes.
Figure 1: Vernier Digital Radiation Monitor.
Image Source: Digital Radiation Monitor manual.
1. Obtain a monitor and stop watch for your team. Set the monitor up to take counts
over a six-minute period.
2. Set your monitor and stop watch close together. Start your stopwatch as soon as you activate
the monitor for counting. Keep your stopwatch running and complete the data table below.
Since your measurements were made at 1 minute intervals, your Change in Counts column
represents the counts per minute (CPM).
Item or Substance:
3. Use the data from the table to determine the
following:
Min CPM = _________
Max CPM =_________
Avg CPM = _________
Time
(min)
Total
Counts
Change in
Counts (from
previous value)
4. What do you observe about the counts that are detected in the different time intervals?
5. Compare your results to those of your classmates. Are they all the same or not? Do
their values show the same patterns as yours did? Are their average values similar to
yours?
6. If they are not the same, what might be the cause for the differences? Design a set
of measurements that could help you determine which causes have the largest
affect.
7. Suppose you need to determine the background radiation because it is your job to
report this in a classroom safety report.
a. Would it be better to measure and report the number of counts in a 5 second
interval, 30 second interval, 60 second interval or 120 second interval? Why?
Explain your choice.
.
b. Would it be better to take one measurement or three measurements? Why?