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The Model 3440 gauge uses a Cesium-137 and an
Americium-241:Beryllium source for taking measurements.
These radioactive sources undergo a natural decay process,
resulting in a gradual loss in the intensity of their radiation. The
time required for the source strength to diminish by 50% is
referred to as the half-life.
To compensate for the source decay and to check proper
operation of the gauge, a daily reference standard count should
be performed. To ensure the highest accuracy possible with the
gauge, it is important to take a daily standard count.
The gauge is equipped with a reference standard block for
taking the standard count.
Site Requirements
Choose a standard count site that meets the following criteria:
i A smooth, dry surface such that the reference standard
block does not rock.
i At least 3 meters (10 ft.) from any large vertical surface.
i At least 10 meters (33 ft.) from any other radioactive source.
i On asphalt, concrete, or compacted soil at least 10
centimeters (4 in.) thick and with a density of at least 1600
kg/m
3
(100 pcf).
NOTE
Always take standard counts using the reference
standard block provided with the gauge.
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