altitude and other factors, such as types of minerals in the ground. Levels differ
at different distances from the ground, and may differ even in different areas of
the same room. To accurately interpret the readings you get on the Digilert 100,
it is a good idea to establish the normal background radiation level for each
area you plan to monitor. You can do this with a total/timed count. Use the
steps shown in "Taking a Timed Total Count" in Chapter 3 to get a ten-minute
average.
A ten-minute average is moderately accurate. You can repeat it several times
and see how close the averages are. To establish a more accurate average,
take a one-hour count. In some locations, you may want to take a longer count,
for example, 12 hours. If you need to determine whether there is prior
contamination, take averages in several locations and compare the averages.
Environmental Area Monitoring
You can keep the Digilert 100 in CPM or mR/hr mode whenever you want to
monitor the ambient radiation, and look at it from time to time to check for
elevated readings. You can also use Alert mode to warn you if the radiation
increases above the alert level.
If you suspect an increase in ambient radiation, use the timer to take a five or
ten minute count, and compare the average to your average background count.
If you suspect an increase that is too small to detect with a short timed reading,
you can take a longer count (for example 6, 12, or 24 hours).
Checking an Object
To check an object, put the Digilert 100 next to it. The end window should be
facing and close to the object; otherwise you may miss alpha and low-level beta
radiation. If you want to find out if an object is slightly radioactive, place the
Digilert 100 next to it and take a timed count over an appropriate period of time.
When you are not using the end window, hold the Digilert 100 so that the side
wall of the tube is as close as possible to the object. Alinging the symbol
marking the center of the detector close to the object is the best position. The
illustration at the right shows the position of the Geiger tube in the Digilert 100.
To measure as much as possible of the radioactivity of an object, place the
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