F3 – Setup Menu
Gem-5 User’s Manual 125
Line Items
Calibration Source: This is the same item as described in the F5 – Group Settings
screen but applies to the selected zone only. It identifies the calibration source that
will be used for the next calibration, i.e. if F1 is pressed. This could be different from
the source that was used for previous calibration (see Source Used, below). It
combines the Source ID and Isotope descriptions as entered in the F9 – Edit
Calibration Source List. Use the + and - keys to scroll through the available sources
from the Calibration Source List.
Note: The Calibration Source properties can be edited only in the F9 – Edit
Calibration Source List screen. The F3 – Calibration screen imports data
from the Calibration Source List when required so that it always uses the
most recent information.
The Source Activity, Source Date, and Source Dimension for the selected source, as
listed in the Calibration Source List, are displayed also for information only.
Calibration Distance: enter the distance the calibration source is placed from the
detectors before starting the calibration collection. The range is from 0 (on contact)
to 100 cm and is specified in cm. This allows the distance used for calibrating (and
Alarm Test) to be documented. The default is the recommended distance assumed
for the derived efficiency (see Calibrate on page 89).
Detector Dimension: the length and width of the detector section (in cm). Factory
Default values are correct for the detectors installed at the factory. The range is from
0 cm to 100 cm. The detector dimensions are compared with the calibration source
dimensions so that the visible area of the source can be calculated automatically if the
source is bigger than the detector. The value of 0 is a special case indicating that the
dimensions will not be used in calculations. On exiting this screen, the larger
dimension is forced into the length (first) dimension.
Default Detector Dimension values for sum zones are shown as zero, indicating that
calculations will be based on the geometry of the constituent detectors.
Note: Calibration Distance and Detector Dimension are hidden for Sum Zones.
Area of Source Visible: this calculated number expresses the visible component of
the calibration source as a percentage. This value is less than 100% when the source
is larger than the detection or sum zone in one or both of its dimensions. Assuming a
uniformly distributed area source, the decay-corrected source strength is multiplied
by this percentage to calculate the current visible source strength (see next item). To
disable the source size correction set one of the detector dimensions to zero.
Current Visible Activity: This is the decay-corrected calibration source strength
seen by the detector, after factoring in the source area visible (see previous item).
Self Shield Factor: This adjusts the background level subtracted during calibration
collections to compensate for a person’s body or source container absorbing (i.e.
shielding) some of the background radiation. Only in rare circumstances would this
setting be changed from the factory default (1.0). See Footnote 13 on page 215 for
the special case for gamma detectors.
To Next Page
Loading...
Need help?
General
