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A core section measurement consists of two positions, counted for at least 5 min each for a total of 16 measurements per section. A typical ~150 cm whole-round core section is wiped dry and placed in a boat on the loading end of the instrument, where a barcode scanner records the sample number and imports sample information from the encoded label. The length of the sample is determined and manually enteredrecord via the text-id. The boat stops at position #1, where the top of the boat is centered above position past (usually 10cm) the center of Sensor #8 (starboard most detector). After measuring at position #1 for a user-defined time period (not less than 5 min), the boat moves 10 cm further inward outward (port) and begins counting at position #2. When the run completes, the section returns to the starting position and can be unloaded.

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  • Make sure to use the values shown for the NGR (Fig. 13).
  • User should be familiar with the M-Drive motor system prior to adjusting these settings.
  • The relationship between motor revolutions and linear motion of the track is defined in this window and is critical to both safe and accurate operation.
  • Select Axis: In the case of the SRM NGR it is always X.
  • Encoder Pulses/rev: Defined by the manufacturer of the M-Drive as 2048.
  • Screw Pitch: Set to 0.0627 (the ratio of 2048 steps per revolution and chain displacement (cm) as a function of the drive gears diameter).
  • Gear Ratio: There is not a reduction gear so this value is set to 1.
  • Direction: Clockwise rotation moves the tray in a positive direction (from home to end of track).
  • Click the Open Utilities and Test button to open the Motion Utility window (Fig. 14) and test the settings. Click Close to exit this window.
  • Click Done to save the values or Cancel to return to previous values.
     
    Figure 13- NGR Motor and Track Options Setup Window

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  • Select Axis: In the case of the NGR it is always X.
  • Max Section Length: Maximum length of section that can be placed in the track. This value is set to 160 cm.
  • Track Length: Distance in cm between the limit switches. Use the Motion Utility (Fig. 14) to determine this value by moving from limit switch to limit switch plus the length of the tray used.
  • Load and Unload: For the SRM NGR set to 0. This will always bring the tray back to the sample load end after a measurement sequence.
  • Top-of-Section Switch: Not used.
  • Top-of-Section Switch Offset: Not used.
  • Fast Offset: Not used.
  • Run Out Switch?: Not used.
  • Click the Open Utilities and Test button to open the Motion Utility window (Fig. 15) and test the settings. Click Close to exit this window.
  • Click Done to save the settings. Click Cancel to return to previous values.
     
    Figure 15- NGR Fixed Positions Window

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Step-by-step procedure for setting the NaI(Tl) detector bias voltage:

  1. Place the aluminum calibration core (lead source holder ) on the titanium boat, making sure that hole #8 holder is on the NGR chamber end and hole #1 is closer to the catwalk hatchslotted on the Ti boat correctly (i.e., fig xx). Place both the 137Cs and 60Co calibration sources in the white PFTE holder and insert it into the hole between #1 and #2 (i.e., hole 2-1) as for the energy calibration procedure above.
  2. Ensure no obstructions are on the track or inside the chamber.
  3. From the main NGRL screen, select the Track Utility dialog box and click “Calibration position” to send the core into the chamber.
  4. Open the ORTEC Maestro program. From the top menu choose Display/Detector/00001 PC to open the signal spectrum for NaI(Tl) detector #1. Clear the previous spectrum, if any.
  5. On the Acquire menu, select MCB Properties and on the properties window, ensure that the gate is set to “anticoincidence” on the ADC tab and that the Live time on the Presets tab is approximately 60 seconds. Close the properties box.
  6. On the Acquire menu, click on Start and allow the spectrum to be collected. It should look like one above (Fig. 25). Bring the Maestro cursor to the middle of the 137Cs peak and check the corresponding channel number on the bottom of the screen. If this number is 224 to 228, a bias voltage correction is not necessary, but could still be performed if desired. (Expected behavior is for the channel number for 137Cs to be 226±2 channels (Fig. 26).)
  7. If the drift is sufficiently large to require an adjustment, or if the spectrum appears compressed or stretched compared to the other detectors, perform a bias voltage tuning.
  8. Use a multimeter. Set it to DC current in the millivolt range. Read the voltage in the bias adjustment box. The multimeter’s black probe goes into the white fitting and the red probe into the appropriate red fitting for the detector being examined (see Fig. 27).
  9. Note the current voltage setting and the position of the pulser channel (if the pulser is used), the 137Cs 662 keV peak position, and the 60Co 1170 and 1330 keV peak positions in the table below (Table 1).

  10. Using the potentiometer screw just above (aft of) the red fitting, gently turn the screw to increase voltage (clockwise rotation) if the 137Cs peak is less than channel 226, or to decrease voltage (counterclockwise rotation) if the 137Cs peak is greater than channel 226. Note that you must rerun the 60-second acquisition (step 6) each time to see the new channel.

  11. Once you have set the 137Cs peak close enough to channel 226, record the new voltage setting and the new positions of the pulser channel, the 137Cs 662 keV peak, and the 60Co 1170 and 1330 keV peaks on the table.

  12. You must now set the software calibration as noted in the “Energy Calibration Procedure” section above. Once you have done this for detectors #1 and #2, repeat for the other detector pairs.

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  1. Place the core section in the tray and ensure the top of the section is against the top of the boat.
    Note: the PMTs for the door plastic scintillators are visible (and exposed to potential damage) so significant care must be taken during core section movement to avoid the possibility of damaging the detector or PMTs.
  2. Place the core section in the titanium boat on the NGR delivery system loading track. Ensure the blue end of the core section is against the leading edge of the boat (closest to the NGR door
  3. Open NGR Core Analyzer (Fig. 30), which is usually found on the NGR’s workstation desktop. If the configuration files are corrupted or missing, load them from the Main control menu by choosing Configuration.
  4. Press the Scan button (Fig. 30, #1) on the NGR Core Analyzer screen to initiate a run. The Sample Information dialog window will appear (Fig. 30, #2).
    Important! Ensure that the cursor bar is blinking in the Text ID box before scanning the section’s barcode. The NGRL can be set to run without a sample identifier if no Text ID is present and this will waste time.
  5. Ensure the barcode reader has read the sample identification and the Text ID and Sample Name, fields have been completed on the Sample Information screen. Sample length is very important for proper edge correction and must be entered manually. (Text ID and Sample Name fields can also be entered manually if the barcode won’t scan.)
    Note: the “Run the Experiment” button will not activate unless a length >0.0 cm is entered in the Sample Length field. The user must click elsewhere, tab out of the field, or click press enter (user’s choice) in order for the software to register the entered value and enable the “Run the Experiment” button.

    Figure 30. NGRL Core Analyzer Screen, Ready to Start Scan.

  6. After all necessary lines are filled click “Run the Experiment” in the Sample Information window and the boat will begin moving. The boat will proceed automatically into the chamber without further intervention, so be sure the track is clear of obstructions!
  7. As soon as the sample reaches measurement position I, the measurement will begin. Eight channels will collect gamma ray counts from measurement points along the core section in Position #1 for a user-defined time period.
  8. The core will move automatically forward 10 cm into Position #2 and again collect data for another eight positions (for a total of 16 measurement positions every 10 cm).
  9. As the sensors take measurements, counts are plotted vs. sensor number on the mainscreen. Hit the Detail/Summary button at the upper right of the screen to switch between the histogram vs. binned mode displays. The button name changes from Summary to Detail, depending on which view is selected (Fig. 31 and 32).

    Image Modified

    Figure 31. Core Analyzer Screen Showing Histogram.

    Image Modified

    Figure 32. Core Analyzer Screen in

    10. Binned Mode

  10. Individual Detector Reading Display.

  11. Elapsed time (on the left side of window) during normal run (e.g., with 10 min acquisition time per position should go up to 21–22 min).
  12. After data acquisition finishes, the boat will retract from the NGR chamber automatically. It is therefore important not to have anything blocking the actuator’s path!
  13. The analysis is now complete.

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