Alarm Test
Gem-5 User’s Manual 71
When performing an Alarm Test on a foot (or Gamma body, Gamma shoe or head)
zone when Count Gamma Shoe=
4
In Two Steps is set to “YES” in the
F1 – Common Values screen, the check source should be left on each foot position
for two counting periods. If the result is “CLEAN” on the first count, this should be
ignored.
The frequency of performing Alarm Tests is determined by the facility policy.
Staff who do daily cleaning tasks could do this test, or regular service maintenance or
radiation control personnel could perform it.
Note: Sources used for alarm testing to verify monitor sensitivity and alarm
function must have activities at or above the alarm set point.
It is imperative that the radionuclide(s) used for alarm testing are the same as
those used for calibration and are placed in the same geometry as the
calibration geometry. This is necessary to provide a consistent measure of
detector and monitor function.
Conversely, using too large a source could fail to identify a low efficiency
detector or an incorrect configuration setting.
If short-lived radionuclide(s) are used as alarm test sources, ensure that they
are replaced (as appropriate) before they have decayed to activities, which are
below their respective alarm set points.
On alpha/beta/gamma models, separate sources would be required to verify
the alpha, beta, and gamma alarm responses.
If a facility routinely performs alarm tests using appropriate check sources then re
calibration more frequently than once a year is unnecessary, since the alarm test
provides verification of detector efficiency, alarm release limit and proper system
operation. Under these conditions, there is nothing gained by performing calibrations
more frequently.
The suggested method of operation therefore, following initial installation, is to
perform alarm tests weekly, and to calibrate only detectors that are being replaced (or
use the Default Calibration). This will provide the most effective life cycle costing to
the maintenance group while also providing proof that the unit is fulfilling the
facility’s requirements for monitoring personnel at radiation control boundaries. An
annual full calibration should be considered for detectors that have not been
calibrated within the previous year.
In Walk-Through mode, verify that the check source is detected by walking through
the monitor with the source attached in various body positions, one of which should
be in the middle of the monitor to simulate a “worst case”. This requires that the
Alarm Test Type be set to “Coverage Test” in the F7 – Alarm Test Settings on page
133.
.
4
And/or (gamma) Item(s), Gamma Body, (Gamma) Shoe, and/or (Gamma) Head
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