Ludlum Measurements 44-110, Manual

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Model 44-110 & 44-110-1 Large Area Tritium Detectors
Page 1
1. GENERAL
The Ludlum Model 44-110 and 44-110-1
Tritium Detectors are large area windowless
gas flow proportional detectors used for
detecting fixed tritium contamination. Due to
the energy of tritium, certain restraints of the
detector make it marginally more difficult to
use than many of the other types of detectors.
A count rate instrument that is capable of
providing an operating voltage of 1750 V
±
50
V and a threshold of 4 mV ±1 mV is required.
The Model 44-110-1 is different from the
Model 44-110 in that it is equipped with a
multi-position gas flow selector valve. The
selections available by rotary switch are
OFF
,
PURGE
(7 liters/min),
NORMAL
(1 liter/min),
and
STANDBY
(20 cc/min).
The Model 44-110-1 also differs in the open
surface area of the face plate and the type of
handle. Window opening of the Model 44-
110-1 is 150 × 15 mm.
2. SENSITIVITY
Typical sensitivity of the Model 44-110 or
44-110-1 is from 30% to 45% 4pi. Due to
degradation of count from dust in the open
chamber area, 30% efficiency is stated for
determining minimum detectable activity
(MDA).
The MDA (calculated per NUREG/ CR-
5849), at 30% efficiency in a 400 cpm
background and a count rate instrument with
an approximate 22-second response time, is
approximately 503 dpm/100 cm
2
.
3. COUNTING GAS
Recommend 300 ft
3
P-10 cylinder mounted
on a cylinder truck for mobile gas supply.
Estimated time of operation for one 300 ft
3
cylinder is approximately 40 hours.
4. OPERATION
1. Connect the P-10 counting gas and
HV/signal cable to the detector. Place
the detector on an uncontaminated flat
surface and turn the gas on. Check to
see that the switch on the detector is in
the
ON
or
PURGE
position. The count
rate will increase as the detector purges,
until the maximum background level of
approximately 400 cpm is reached.
Purge time for the Model 44-110 is
approximately 30 seconds with a gas
flow rate of 3 to 4 liters per minute.
Purge time for the Model 44-110-1 is
ATTENTION:
Prior to use, it is necessary to remove the aluminum insert inside the gas connector. With it
still installed, the user cannot plug in the gas supply. The purpose of the insert is to
equalize the pressure inside the probe and to prevent the window from rupturing during
shipping and transport in an aircraft. Remove it by releasing the locking collar while
turning the probe upside down or simply pulling it out while releasing the collar. Once the
aluminum insert is removed, the connector that is attached to the gas hose can be plugged
in.