Sper Scientific 840007 Radiation Detection Meter User Manual
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beeps, at a rate that increases as the radiation level in-
creases. Although this range is not as accurate as the dis-
played range, beeping will begin approximately at 15mR/hr.
A continuous beep occurs approximately at 20mR/hr.
These built-in ranges greatly simplify operation and allow
reasonably quick and accurate measurements to be made.
The meter is not intended to indicate levels below 0.1 mR/
hr., therefore, readings taken below this level should be
considered extremely crude. However, such low level
measurements can be made by simply counting the clicks
over a period of time, much like taking a person's pulse,
and expressing the result as clicks (or counts) per minute.
0.1 mR/hr, on the meter corresponds to about 330 counts
per minute.
INTERPRETING READINGS
Health physics, the field that pertains to radiation and its
effects on man, is very complex, and theories and con-
clusions are constantly being updated as information be-
comes available. Data from occupational exposure, animal
studies, and events like Hiroshima and Nagasaki have
fairly well established the maximum safe exposure limits for
man. Whether low level radiation causes cancer and birth
defects is still being debated. Delayed effect, which could
take years to develop, is difficult to study, and therefore,
there are no well-defined lower limits on ionizing radiation.
Two publications entitled "Hormesis with Ionizing Radia-
tion," 1980 and "Radiation Hormesis," 1991 (CRC Press,
Boca Raton) present over one thousand examples of statis-
tically valid data showing no physiological harm in verte-
brates from whole body exposures to low dose radiation
(<20mGy/y).
As previously mentioned in the section on operation, the
units mR/hr (milli-Roentgen per hour, or 1/1000th of a Ro-
entgen per hour) pertain only to gamma radiation. Often
other units of measurement similar to mR/hr are used. The
term "REM" (Roentgen Equivalent Man) includes the af-
fects of beta, alpha and neutron radiation. Measurement in
REMs is more complete as radiation affects man, but such
measurements are a complicated combination of many
measurements each made with specialized detectors.