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194 ATOMLAB 500 DOSE CALIBRATOR
Fluctuations In Activity Measurements
When the system is displaying activity for the more common isotopes, the electrometer
continually averages the data it receives from the detector. This ensures, for most readings, a
stable activity display.
After you insert an isotope into the detector and select the properly calibrated key, the display
may vary at low activity values as the system acquires the new data. After a short time the
activity display will stabilize, with expected fluctuations described below. If the display
continues to fluctuate, and you have verified it is not because of a high calibration value,
consult Biodex customer service department.
Display Fluctuations For High Calibration Values
For some isotopes which require a high calibration value, you may observe fluctuations of ±0.5
µCi or more. Keep in mind that the calibration value for an isotope is related to gain of the
electrometer, or by what factor the electrometer has to amplify the signal from the detector.
the calibration for Tc-99m is 37.1, and a reading of 10 µCi for Tc-99m is equivalent to 160 to
180 femtoamps of current measured by the electrometer. High calibration values impact gains so
that the electrometer amplifies inherent noise to a greater degree. Thus, greater fluctuations are
observed in the activity display.
For instance, the calibration value for Co-60 is 5.0. The fluctuation due to noise probably would not
be noticeable (±0.01 µCi). The fluctuation due to noise for Tc-99m (37.1) is approximately ±0.05 µCi.
For an isotope requiring a calibration value of 500 (for P-32 it is 530) the fluctuation will be ±0.5 µCi
or more.
Mo-99 Fluctuations
The Atomlab Dose Calibrator begins averaging display data the moment you press the Mo-99
key (calibration value =175). This means that at first the fluctuations will seem relatively high
before gradually decreasing. This is why the Atomlab Dose Calibrator provides the 30-second
countdown. In addition, the relatively high calibration value means the fluctuation due to
inherent noise will be slightly higher than for the other common isotopes. Again, these
fluctuations are to be expected and do not require any action on your part.
Unexpected Readings
If for some reason you suspect that the reading on the activity display is inaccurate, ensure
that the calibration value for the proper isotope selection key is correct.
Detector Service
CAUTION: Only qualified service personnel should remove the detector cover. There is an
electrical shock hazard. Components under cover operate at 350 volts. The detector bias
supply capacitors require at least two weeks, with power disconnected, to discharge to
less than 50 volts.
ATTENTION: On ne doit confier qu'à un personnel d'entretien qualifié le soin de déposer le
couvercle de la chambre d'ionisation. Il y risque de danger électronique. Les
composants sous le couvercle fonctionnent sous une tension d'environ 350V. La chambre
d'ionisation est dotée de condensateurs qui nécessitent au moins deux semaines
d'alimentation débranchée pour se décharger à moins de 50V.
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