SAIC Exploranium – GR-135 System Manual page: 35
In this case users are advised to stabilize the system in the DS and then repeating the
measurement. If the same “UNIDENTIFIED ISOTOPE” message is received again then this
truly is an isotope whose characteristics are not in the system library.
12H, 24H – if either of these parameters are selected it means that 12 hours (12H) or 24 hours (24H)
after removing the system from the DS – a message will appear on the GR135 display requiring the
system to be returned to the DS for system stabilization. The standard setting is 24 hours as this is a
reasonable time for system operation without the super accurate requirement of DS stabilization.
Most AUTO mode users keep the unit in the DS when not in use so in most cases this parameters
effects are not seen
10.3 IDENTIFY
There are 4 sub-sections – DETECTOR, NaI, CZT, NEUTRON
10.3.1 DETECTOR
a) DETECTOR – this selects the detector used in the IDENTIFY mode, choices are
AUTO, NaI, CZT
AUTO – normal selection. In this mode the system starts off with the NaI detector and if required
the CZT detector is automatically enabled
NOTE: ALWAYS SET THIS MODE TO AUTO UNLESS SPECIAL CZT EXPERIMENTS
ARE BEING CARRIED OUT. IT IS ESSENTIAL THAT FOR NORMAL OPERATION
THAT THIS IS SET TO AUTO OR CORRECT SYSTEM OPERATION IS IMPAIRED IN
THE AUTO MODE
NaI – selects only
the Sodium-Iodide (NaI) detector (CZT is disabled if present)
CZT – this selects only the optional CZT detector (NaI is disabled)
b) PILEUP – this sets the Pile-up rejector ON or OFF
The Pile-up rejector only applies to the NaI detector, as the relative inefficiency of the CZT detector
does not require this function. So this parameter controls only the NaI data collection, CZT analysis
automatically disables the Pile-Up detector regardless of how this parameter is set. For the NaI
detector this item automatically detects if 2 pulses are impacting the detector simultaneously.
Normally such pulses would combine to produce an incorrect energy pulse. The Pile-up rejector
automatically rejects BOTH pulses and changes the Dead-Time counter to compensate. The OFF
selection permits system testing for special applications.
c) PEAK LIMIT – selections are 10, 15, 20, 25,
30, 35, 40, 45, 50
This parameter is essentially a “sensitivity” setting for Nuclide Identification.
During Nuclide Identification, a spectrum is taken then a Peak Analysis engine is used to select
significant peaks. This engine suppresses backscatter peaks etc and other spurious peaks during its
action and then defines a list of all peaks found. For each peak the error on that peak is computed
and the amplitude of the peak is determined in Standard-Deviation (SD) units.
The PEAK LIMIT setting is then used to remove low amplitude peaks. So if 30 is selected (the
default value) then any peak 2.9 SDs or below is eliminated before the peak list is used for Nuclide
Identification.
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