F5 – Information Menu
Gem-5 User’s Manual 247
The assigned sequential Zone Number shown in small font at the top right of the
screen is used consistently on service mode screens and printouts where information
for individual zones is shown; this number is a convenient way of locating the zone
of interest when switching between screens.
The text above the graph indicates the count times for the selected zone as well as the
worst-case zone, that is, the zone that requires the longest counting time, not
considering “Count Gamma Body In Two Steps”. This will normally be the zone that
is controlling the overall counting time for the monitor. The actual counting time
used would be the time displayed for the limiting-case zone rounded up to the next
highest integer number of seconds, except where “Count Gamma Body In Two
Steps” has the effect of reducing the required counting time.
The two vertical green lines (one at 2,000 cps in the example shown above) indicate
the current background rate (R
B
) and occupied self shield adjusted background rate
(R
b
), respectively, for the selected zone. If the occupied self shield factor is 1 then
only one green line is visible (as is the case above). The required monitor time for
the selected zone is given by the intersection of the (lower) green line with the
(yellow) curve. In the example shown above, the self shield adjusted background rate
of 3,000 cps for Detector Sum Zone 7-8 requires 1.7 seconds of monitoring time. If
the background rate were increased to 10000 cps, the required monitoring time would
be about 12 seconds. The limiting-case zone is Gamma Sum Zone All, which
requires 2.4 seconds. Under these conditions, the actual counting time would be
rounded up to 3 seconds, unless “Count Gamma Body In Two Steps” has the effect of
reducing the required counting time.
The two horizontal red lines indicate the minimum (3 s) and maximum (30 s) monitor
times, as set in the F2 – Wait Timeouts screen. The vertical red line constructed
where the maximum monitor time (30 s) intersects the (yellow) curve indicates the
background rate that would take the unit out of service due to high background
(maximum monitor time exceeded). For the zone shown in the figure above, this
would occur at 30,000 cps.
A complete table of counting times required for each detection zone, as well as a
description (makeup of sum zones) of each zone, can be found on the F6 – Monitor
Zone Status screen (on page 250).
Shift+F4 - Monitor Time vs. Bkg Time
To access the Monitor Time vs. Background Time Sum Zone Screen, select the
Shift+F4 - Monitor Time vs. Background Time menu item. The Graph Monitor Time
vs. Background Time aids in setting F1
−
Zone Configuration screen, Background
Average Period.
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