Sper Scientific 840026 Radiation Detection Meter - Manual (Page 5)

5
THIS IS THE POSITION IN WHICH TO HOLD THE GEI-
GER COUNTER TO TAKE READINGS. It is important to
understand this, for misleadingly high meter readings can
result from allowing Beta rays to be measured with the
gamma rays. The meter scale is calibrated for gamma ra-
diation.
FIG. 2
READINGS
There are two Sper Scientific Radiation Monitor models:
840007 - 0.1 to 10mR/hr
840026 - 0 to 100mR/hr
All units are tested at the factory using gamma radiation.
The radioactive gamma source used in the factory is Ce-
sium-137 that has been Beta shielded with .062" of Alumi-
num, and measuring radioisotopes other than Cesium-137
introduces some error. The error caused by this is usually
very little. Note that in the case of X-rays, the unit is very
sensitive and subsequently meter readings should be di-
vided by about 5.
The 840026 was calibrated. For how often you have to cali-
brate your unit, check with your local NRC. However, you
must calibrate after each repair or change of G-M tube.
Since the 840026 radiation monitor has an oscillator, it can
be readily adjusted/calibrated by turning the screw on the
oscillator with a small screwdriver in the desired direction:
turning clockwise to decrease the reading; counter clock-
wise to increase. This calibration should be done at a li-
censed laboratory.
In addition to the analog meter, a special extended range
has been designed into the 840007 unit. At radiation levels
that are in excess of the meter scale, the unit will emit