A sievert is the standard international measurement of dose. One sievert is
equivalent to one hundred rems. A microsievert ( Sv) is one millionth of a
sievert.
A curie is the amount of radioactive material that decays at the rate of 37 billion
disintegrations per second, approximately the decay rate of one gram of radium.
Microcuries (millionths of a curie) and picocuries (trillionths of a curie) are also
often used as units of measurement.
A bequerel (Bq) is equivalent to one disintegration per second.
Determining What Is a High Reading
Due to the random nature of radioactivity, the Digilert 100 reading varies from
minute to minute. In one location with only background radiation, the reading in
mR/hr might vary in ten minutes from .007 to .018. In an hour, the reading
might vary from .004 to .021. The averages for both periods would be very
close.
Normal radiation levels in different locations can vary greatly due to soil
composition, altitude, and other factors. For example, normal background at
10,000 feet might be double that at sea level. On an airplane, the radiation at
35,000 to 40,000 feet may be as much as 30 to 50 times the normal level on
the ground.
When monitoring radiation levels in one location, it's helpful to determine what
reading is the highest you can normally expect to see in that location. If you
use Alert mode, you want to set the alert level to one that rarely gives a false
alarm, yet sounds the alert when the radiation is higher than normal.
A single alert may occur occasionally and is not significant unless there is also
an elevation in the average count. If you suspect an elevation and you have
previously taken an average background count in the same location, you can
take a total count to get the current average count for 30 minutes or another
period. You can then compare the current average to the previous average to
see whether there is an elevation. See "Taking a Timed Total Count" in Chapter
3 for more information.
19
