ORTEC Detective X, Руководство пользователя

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1107231N / 082020 4. DETECTIVE X APPLICATION
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Several factors can cause the system gain to change, and the K-40 reference peak to shift slightly such that
the automatic circuitry must re-center the peak in its expected histogram region. The most significant of
these are detector temperature and long-term electronics drift. Both of these changes occur at an extremely
slow rate. This means these changes can be accurately tracked by the gain stabilizer, even when the
concentration of environmental K-40 is very low. Note that detector temperature is regulated in the
Detective X. However, the bulk temperature of the detector element will continue to change by very small
increments for several hours after system has reached the threshold operating temperature and the status
has changed to
READY
. The gain stabilizer can easily correct for this slowly moving effect.
The gain stabilizer typically makes adjustments very gradually. Note, however, that if the instrument is
subjected to a significant mechanical shock, the gain can change instantaneously, forcing the stabilizer to
quickly correct for the situation. Rapid movement of the stabilizer is an indication that the system is still
working to put the K-40 peak in the correct location. This condition is indicated by a “ Stabilizer rapid
movement ” system error, and the status is
NOT READY
until the stabilizer zeroes on its new value.
Reestablishment should take no more than 30 minutes.
The gain stabilizer can adjust the amplifier gain to move the K-40 peak the equivalent of 7.5 keV either up-
or down-channel, as needed, which is more than enough under normal circumstances. However, in atypical
circumstances (such as the shock mentioned above), ±7.5 keV may not be sufficient. The Stabilizer out of
range error will be displayed and the status will change to
NOT READY
. This error will typically be preceded
by a “ Stabilizer rapid movement ” error as adjustments are applied quickly in an effort to correct the
situation. The current Gain Stabilizer adjustment is shown on the Status screen accessible from Settings (see
Figure 85). This figure shows that the stabilizer has currently made an adjustment equivalent to 1.5 keV,
which is 18.4% of the available range. If this value is beyond about 60%, it is time to consider recalibrating
the unit. Otherwise, the gain stabilizer may reach the limit of its ability to correct the K-40 peak position while
the user is out in the field, in which case, the status will change to
NOT READY
until the unit is recalibrated.
Figure 85. Current Gain Stabilizer Adjustment
4.15.2 Calibrating the Detective X
The energy calibration is a single-point calibration that simply adjusts the system gain. The shape of the
calibration curve is fixed and has been determined at the factory. Calibration is easy to perform with a user-
supplied, nominal 1-microcurie (μCi) cesium (Cs)-137 check source. The process typically takes less than
5 minutes.