Ludlum Measurements 44-110, Manual

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Model 44-110 & 44-110-1 Large Area Tritium Detectors
Page 2
approximately 15 seconds with a gas
flow rate of 7 liters per minute. After
obtaining the background measurement,
the gas valve can be turned to
OFF
(Model 44-110) or
STANDBY
(Model
44-110-1) until the start of the survey.
2.
For surveying, place the detector on the
surface to be assessed and turn the gas
valve to
ON
or
NORMAL
. Observe the
count-rate meter until the maximum
background count is reached. Slowly
slide the detector along the surface,
pausing for a moment for each detector
width. If any increase in count rate
above background is observed, keep the
detector over the suspected area until
maximum reading is obtained.
3.
Survey Considerations
a. Using the Model 44-110, very smooth
surfaces such as tile floors and lab
bench tops can be surveyed very
effectively and rapidly because the
detector can be purged once and then
slid over the survey surface area.
b. The Model 44-110-1 is more suited for
surveying less regular surfaces and for
personnel frisking.
c. When surveying less regular surfaces
with the Model 44-110, the probe
cannot be slid across the surface and
re-purged for each measurement.
d. Irregular, curved, and very small
surfaces, such as drain pipes, table
legs, etc., cannot be effectively
assessed using either of these
detectors.
NOTE
In order to prevent residue forming on the
chamber and anode wires, the detector
should not be used on very dirty or dusty
surfaces. Extreme humidity in the air (in
excess of 85%) and moisture on surfaces
can cause the detector to behave
erratically.
Therefore, it is not
recommended to use the detector in high
humidity or in moist conditions.
Static electricity on a surface is sufficient
to prevent some tritium beta particles
from escaping from the surface, thus
reducing calculated surface emission.
5. MAINTENANCE
Dust on the anode wires may impair the
efficiency. This is manifested by changes in
the background count rate. A background
count rate change of ±150 cpm may be due to
dust accumulation, rather than an actual
change
in background or low-level
contamination. A careful assessment is
required to determine the exact cause of
variation in count.
Surveying in a dusty environment may
require cleaning the anode wires and chamber
several times a day.
Cleaning anode wires:
Use a dust remover spray such as those used
by photographers, followed by a spray of
electrical contact cleaner. The cleaner or
solvent must be 100% residue free.
CAUTION
When cleaning the counting chamber, be
extremely careful not to damage or break the
delicate anode wires.