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• Take your time. Let the electronics settle. This is not a race.
• Voltages across any given NaI(Tl) detector may be monitored with a volt-meter at the bias box with 8 red touch points and a white single ground point.
• Do not change the voltage at any NaI(Tl) detector at the junction box!!! Remember if you need to switch off the High Voltage you must switch off the whole right-hand NIM crate (right-hand NIM crate button in Fig. 12), which will turn the high voltage off from all NaI(Tl) detectors simultaneously.
• Follow all steps in the Partial Shutdown procedure first.
• Turn off the power switch to the iSEG voltage control crate (behind iSEG unit).
• Turn off the fast signal processing electronics (Fig. 13; leftmost NIM rack).
• Shut down the computer.

1. Turn off the master power switch above the middle NIM rack (blue circle in Fig.

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1. 13The fans are connected to the uninterruptable power supply (UPS) and must be unplugged to turn off.
   
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   Figure 13. Master Power Switch.

    

   Startup Procedure

   Before proceeding, the air conditioning system should be functioning and atmospheric conditions stable. If stable, ensure the equipment surfaces are dry. Wait at least 4 hours after the air conditioning turns on.

   Note: Allow the exterior surfaces to dry by evaporation so there is some assurance the internal surfaces are dry as well.

   If the A/C is stable and the instrument surfaces are dry for 4 hours after partial or full shutdown, start the NGRL as follows:

Ensure the fans are plugged in and working.

1. Turn on the master power button above the middle NIM rack (blue circle in Fig. 13).
2. Turn on the computer.
3. Turn on the NaI(Tl) detector electronics (right-hand NIM rack next to iSEG crate, the right red circle in Fig. 13), only after ensuring that the fan under it is working.
4. Turn on the fast signal processing electronics (left-hand NIM rack, the left red circle in Fig. 13).
5. Turn on the iSEG voltage crate power found behind the unit near the power cord.
6. Launch the iSEG control software at the NGR computer (Fig. 14).

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Figure 14. iSEG Hard ware Setup and Main screen. The controller cards may be the EHS or EHQ model and are labeled accordingly.

Make sure the voltages (Vset) for ESQ00/EHS00 and EHQ01/EHS01 are set (Fig. 15). Modify the Vset fields as follows:

Channel 0 = 0 (unused and available for spare channel)

Channels 1 and 7 = 1100 V (plastic scintillators in the doors)

All other channels = 1300 V (shell-shaped plastic scintillators)

If one of the channels on the EHS/EHQ modules has failed, Channel 0 may be in use—be sure you understand which scintillators are connected to which channels, because the door and hoop PMTs require different operating voltages! 

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Figure 15. EHS/EHQ 00 and 01 iSEG Multi-Channel HIgh-Voltage Modules Screens; VRamp and IRamp fields are circled in red.

Make sure voltage ramp (VRamp) is 5% or lower and the current ramp (IRamp) is 50% or lower. The iSEG software does not remember these values between sessions!

Click on the Module access menu and click Instructions for all channels > On (ctrl+o) to start ramping up the voltage.

Wait until ramp-up completes (1–2 minutes if proper values are used).

Exit the iSEG program.

Answer No to the prompt when asked to ramp voltages back down. If you answered Yes inadvertently, start again at Step 8.

Background Measurement

Measure the background periodically, whenever the ship changes latitude by more than 1-2 degrees, and at least twice an expedition. A data file is generated for each NaI(Tl) detector and measurement position, utilizing the titanium boat with an empty core liner to create conditions as close as possible to core measurement. The background measurement is taken for a much longer period of time for a good statistical spectrum. Typical measurement time is 300 seconds; the background is normally done for 21,000 seconds (almost 6 hours per measurement position; 12 hours total).

During data reduction for core analysis, the background spectrum is normalized to its equivalent at 300 seconds’ duration. For example, if the background at channel 200 of the spectrum were 6,400 counts in the 21,000-second background experiment, that specific channel’s background would be normalized as follows:

                                    6,400 counts x 300 seconds / 21000 seconds = 91.4 counts

Background procedure

1. Use the empty 150 cm whole-round core liner with the background label; this is normally stored on the top of the core rack next to the NGRL. Load it onto the Ti boat.
2. In the NGRL configuration/System Setup dialog window (Fig. 16) change the settings to: no data reduction, live time, 21,000 seconds acquisition time.
3. In the NGRL configuration/File and Folders window verify the data folder (so you can find the background files later).
4. Click on “Core Analyzer”> “Summary Display” tab, Use the barcode scanner to scan the background label on the core liner.
5. Run the experiment (same run button as for sample analysis); this will take ca. 12 hours.
6. After the run is complete, copy the 16 background files from the c:\data\ngr\ archive to c:\data\ngr\.config\background\[EXP#]\data folder, where EXP# is the current expedition (you will have to create this folder).
7. In the NGRL configuration/File and Folders window indicate (select current folder) this Directory as the background; the files should appear in the window.
8. Important! Return the acquire time to 300 seconds and turn “reduce data” back on.