TAKING THE STANDARD COUNT
The 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.
NOTE
A standard count should be performed after the ACU is
installed before using the gauge to take measurements.
A standard count should also be performed any time the
ACU is disconnected from the gauge.
The gauge is equipped with a reference standard block for taking the
standard count. Place the reference standard block on a dry, flat
surface at least three meters (10 ft) from any large vertical surface
and at least ten meters (33 ft) from any other radioactive source. The
surface should be asphalt, concrete or soil at least ten centimeters (4
in) thick and with a density of at least 100 pcf.
Place the gauge on the reference standard block. The right side of
the gauge, farthest from the handle, should be against the metal butt
plate.
To begin the standard count procedure, press 〈STD〉.
DS= xx MS= xx
New Std Cnt?
To take a new standard count, press 〈ON/YES〉.
Press START for
Standard Count
2–8
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