8. Wipe Testing
The shielded well counter uses a 2" x 2" sodium iodide drilled well crystal integral line detector.
The detector is housed in a lead shield with 1" of lead shielding. There is an optional 1"
additional shielding that can be placed onto the well. The well detector has a 1024 channel
multi-channel analyzer built into its base. The system is designed to allow users to quickly and
simply perform required daily and weekly wipe tests for their department.
The Atomlab 960 Well Counter is designed to use a Cs-137 rod source to perform the daily
automatic calibration function. A series of initial setup functions must be performed before the
well counter can be used. Once these initial setup functions are completed, operators needs
only complete a daily calibration and background count before counting wipes.
The Atomlab 960 Wipe Program uses a full spectrum energy range of 0 to 750 keV, covering
the normal isotopes used in nuclear medicine. One channel is used to accumulate any counts
over 750 keV, allowing the user to know if there is a contaminate with a high energy over 750
keV. Manual Mode can be used for energy above 750 keV.
When performing a wipe test, the unit counts and displays a full spectrum count of 0 to 750
keV. From this full spectrum, the Wipe Program displays the user set wide window and
calculates the net counts in the wide window along with the net dpm’s in the wide window.
The Wipe Program allows the user the option of looking at just a wide window or the wide
window plus the isotopes chosen for that location. The user creates the list of locations to wipe
and this list is stored in memory in the display. Each location can be customized to include
results for specific isotopes and what type of wipe is performed: restricted area, unrestricted,
sealed source or package.
When a wipe is counted, only one count is required for determination of the results for the wide
window and any isotopes associated with that location. Each isotope has an associated window
and the system checks each isotope’s window and calculates the results for the specific
windows from the one wide window count.
If a wipe count registers above the wide window trigger level, the system notifies the operator
that the trigger level has been exceeded. The system also shows if any individual isotopes that
have been made available for this particular location are over the trigger and what the readings
are for each individual isotope listed.
Users have the option to set the displayed results as cpm, dpm, microcuries, or bequerels and
different types of wipe tests can be set to show the results in various units of measurement.
Each type of location has different trigger levels associated with the allowable level of
contamination.
The Atomlab 960 Wipe Program is designed so that the wide window energy range used
for the basic test results can be set by the user, along with the isotope efficiency to be used for
the calculation of the efficiency for the wide window. Typically, a low efficiency isotope is used
for the wide window calculation. If an isotope with a low efficiency is used and the wipe passes
the test, then isotopes that have a higher efficiency automatically pass if they are the
contaminates.
For daily operation of the Atomlab 960 Well Counter, the user first places the Cesium-137 rod
into the well or a CS-137 Disc Source into the Well Holder, then select <Accept> to automatically
perform the calibration.
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