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Contents

Table of Contents
maxLevel 2

Introduction

This guide describes standard operating procedures for the Natural Gamma Radiation Logger (NGRL), designed and built at the Texas A&M University IODP-JRSO facility in 2006-2008. The NGRL measures gamma ray emissions emitted from whole-round core sections, which arise primarily due to the decay of U, Th, and K isotopes. Minerals that fix K, U, and Th, such as clay minerals, are the principal source of natural gamma radiation.

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1. Place the calibration core on the core boat so the round holes face upward. The highest-numbered end (#8) should be closest to the NGR chamber opening (starboard) and the #1 end should be closest to the catwalk hatch.
2. Insert calibration source holder containing both the ⁶⁰Co and ¹³⁷Cs sources into the hole marked 2-1 (Fig. 18). Match up the red marks on the calibration source holder with the marks on the calibration core so that the plastic holder lies flush into its position and will not strike the edge of the NGR chamber opening.
   
   

   Figure 18. Calibration Source Holder.

   
   
   
3. Make sure the track pathway is free from obstacles.  Prepare Bias Voltage Calibration Worksheet (see NGR Log black binder – a blank sheet is attached at the end of this Chapter) to record initial readings.
4. Advance the core boat into the calibration position by using NGR Core Analyzer software, “Track Utility” tab, “Calibration Position”, “Move In button.”
5. Start Maestro. From the Maestro tool bar (Fig. 19) choose the detectors of interest (starting with #1 and #2) and close any other detector windows; your Maestro window should show two channels (Fig. 20). Record initial readings on Worksheet.
   
   
   
   Figure 19. Maestro Aquire menu showing the “MCB Properties” selection.
   
   
   Figure 20. Maestro window showing NaI #1 and NaI #2 detector responses
   
   
6. Clear any results for both windows (right-click in the dark blue area and select “Clear” from the drop-down mouse menu.
7. From the Maestro tool bar open the “Acquire” drop-down menu (Fig. 19) and open “MCB Properties;” this should be the last item on the menu as shown.
   

   Figure 21. Maestro MCB Properties dialog window.

8. For each detector window, In the MCB Properties dialog window (Fig. 21), make sure the Gate setting in the “ADC” tab is set to Anticoincidence. In the “Presets” tab, enter the Live time; exact Live time is not important so long as the Cs and Co peaks are sharp. For a new 1 µCi standard, 60 seconds is sufficient; as the standard ages (esp. the ⁶⁰Co source with its short half-life), it will be necessary to use a longer Live time.
9. For each detector window, right-click in the dark blue area and select “Start” from the mouse window. The progress for the spectra can be observed in the “Pulse Ht Analysis” box on the right side of the Maestro window. Clicking the left mouse button on the spectrum will activate the detector window of interest (Fig. 22.)
   

   Figure 22. Detectors #7 and #8 after acquiring signal from the ¹³⁷Cs and ⁶⁰Co sources; the lower window, detector #8.

10. Click with the left mouse button in the middle of the left (first) peak; this is the ¹³⁷Cs line. Use the zoom functions if it will help see the peak. Go to the tool bar menu, choose the “Calculate,” then “Calibration” commands. A small dialog window will show up (Fig. 23) by peak. Fill the “Calibration (Energy)” field with 662.0, then click OK. Confirm that the calibration units are in keV (not MeV) in the subsequent pop-up window. Peak in channel should be at 226 (+/- 2).
    

    Figure 23. Calibrate dialog window to set a peak’s energy

11. Repeat this operation for the right (third) peak; this is the higher-energy ⁶⁰Co line (448 +/- 2). When the Calibrate dialog window appears, enter 1330.0 in the “Calibration (Energy)” field.
12. Check the calibration by clicking on the top of the middle (second) peak; this is the lower-energy ⁶⁰Co line (394 +/- 2). Go to the Calculate/Calibration dialog window to see if the value in the “Calibration (Energy)” field is close to 1172. If the observed value for the second peak is within +/- 3 keV, you may click OK and proceed to the save step. If the value is outside of this range, click the “Destroy Calibration” button and return to step 11 until in-range values are obtained. It may be necessary to adjust voltage, see following section on Tuning the NGRL Voltage Settings.
13. Save the energy calibration file by clicking the in the detector window and choosing File: Save. Save the calibration file in C:\data\ngr\.config\calibration\[expedition]\date folder (you may have to create this folder, where [expedition] is the current expedition number). Ensure the detector number in the file name matches the actual detector number in the title bar above the spectrum.
14. Retract the core boat to the loading position (Click “Find Home” in the NGR Core Analyzer Software)
15. Remove the source holder from the current position and place it in the next position.
16. Repeat steps 2–8 until all four positions (2-1, 4-3, 6-5, and 8-7) and all eight detectors have been calibrated.
17. After all eight detectors are calibrated and each calibration file is properly saved, close the Maestro window. Make sure to update the NGR’s NGR_configuration/Folders_and_Files dialog window with the correct location of the most recent calibration files. When done, close the configuration window.
    

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Figure 27. Insert the multimeter probes into the bias detector box to measure the voltage. Black to white. Red to red

Table 1. NGRL NaI(Tl) Detector Bias Voltage Table

ORTEC 480 Pulser

It should be noted the ORTEC 480 pulser as well as the pocket pulsers can be used to generate a signal for the NaI(Tl) detectors. At a setting of 30 mV for 50 ¿ input impedance, the signal from the ORTEC 480 will fall onto approximately channel 236. It will be necessary to set the voltage of the pulser with an oscilloscope, and detailed procedures can be found in the NGRL electronics manual.

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It is beyond the scope of this manual to describe the full analytical procedure. Dunlea et al. (2013) provides some guidance on this matter.

Image Added

Figure 28. Thorium Decay Chain. By http://commons.wikimedia.org/wiki/User:BatesIsBack  - http://commons.wikimedia.org/wiki/File:Decay_Chain_of_Thorium.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16983885

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Figure 29. Uranium Decay Chain. By User: Tosaka - File:Decay chain(4n+2, Uranium series).PNG, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=33293646

Time Calibration

Time calibration refers to the process of ensuring that the fast signal from the NaI(Tl) detectors and the fast signal from the plastic detectors occur close enough in time for the coincidence logic modules to work properly. In general terms, a radioactive source (the disk sources) is placed over the detector and the acrylic tube is rotated off its normal position to move the lead spacers away from the plastic scintillators. Gamma and charged particle signals produced by the source are now at such a frequency that the logical coincidence signal is clear and the two detectors’ fast outputs can be aligned to allow the proper anticoincidence VETO signal to be produced.

This procedure is beyond the scope of this manual.

Sample Preparation and Analysis

This section gives instructions for running whole-core sections through the NGR system.

Preparing Samples

It is very important that no water or mud enters the NGR, as the NaI(Tl) detectors are hygroscopic and there is high voltage (~1 kV) applied to the scintillators and photomultipliers. Any mud or dust inside the system will stay there and become an additional source of radioactive background, which will negatively affect all following measurements. All core sections and boat surfaces must be cleaned and wiped dry. Additional preparations include:

• Equilibrate cores to room temperature
• Degas cores as much as possible to avoid “mud worms” in the bore of the NGR
• Use electrical tape to cover holes

Running Samples

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.
   
   Image AddedFigure 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 Added

   Figure 31. Core Analyzer Screen Showing Histogram.

   
   Image Added

   Figure 32. Core Analyzer Screen in Binned Mode Display.

10. 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).
11. 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!
12. The analysis is now complete.

Running the NGR during High Recovery Cruises

During high-recovery cruises, the normal ~11-12 min. NGRL run may be too long to keep up with core flow. The 300 seconds-per-position measurement time is the minimum time needed for good statistical measurements, so reducing it is not recommended. Instead, the software can be instructed to only measure at position #1 or position #2, cutting overall measurement time in half. This will create an interleaved measured/not-measured 10-cm pattern in the data, but the actual data points will be of the normal NGRL data quality.

Again, reducing the NGRL runtime below this single-position measurement is not recommended!

LIMS Integration

Data Handling

Once the run is accepted and the data saved, the results and associated calibration files are saved into the LIMS database. The uploader program (“MUT”) is used to put the files in LIMS; this normally runs in the background, set to automatically upload new files, but can be set to manual upload only. There are two main files to be uploaded:

• ngr_sample_{label id}_{text id}_{timestamp}_{detector/position indicator}.spe
  • This file lists all the raw spectra files generated by a sample measurement experiment at a single measurement position.
  • {label id} corresponds to a name for the sample in LIMS, e.g. 300-1054-A-123H-1 or 419-1200-A-35X-CC.
  • {text id} corresponds to a unique LIMS sample catalog identifier, e.g. SECT103597, SECT10325.
  • {timestamp} disambiguates repeated measurements against the same sample. This timestamp is generated from the NGR host PC’s clock, which should be set to UTC (Zulu time). It is in the format of 4-digit year, 24-hour clock, seconds precision.
  • {detector/position indicator} is in the format of d#p# where d represents detectors 1 to 8 and p represents either position 1 or 2.
• ngr_sample_{label_id}_{text_id}_{timestamp}.xls
  • This file is an Excel file containing all of the summary information and constants used in the calculation of background-corrected, energy threshold-limited data. All eight detector/position combinations are in the single file.
• ngr_sample_{label_id}_{text_id}_{timestamp}.zip
  • The zip file contains all of the calibration spectra, the edge correction table, the background spectra, and another copy of the individual ngr_sample files mentioned above.

The LIMS components for the NGR analysis are as follows:

Data Upload

• Once analysis is complete, open the uploader “MUT.” The icon is a dog face on the desktop but may also be found in START > ALL PROGRAMS > IODP.
• Log in to MUT (the PP technician can help with this).
• Usually, the uploader is set to automatically upload data (check the “automatic” button) but if troubleshooting, it may be desirable to leave this unchecked and trigger upload manually.
• Please remember to put the uploader back on automatic in normal operation so that NGR results are available to other scientists and technicians as soon as sections are completed!

Data Management

Once all sections for the Expedition have been sent through the track, all data needs to be placed in the appropriate folders on data1 (S:\data1).

1. Copy all files from archive and place them in the 4.1 Petrophysics NGR natural gamma folder. Confirm relocation. Delete all files off the local drive.

Health, Safety, and Environment

Safety

NGR operational safety guidelines were developed with regard to automatic equipment operation, laser and radiation sources, high voltage electronics, and general laboratory procedures.

• Keep extraneous items and body parts away from the moving actuators, titanium boat, and motor.
• The doors are extremely heavy (ca. 400 kg) and care should be taken when using the chain hoist to open or close the rear (starboard) door for calibration.
• The track system has an emergency stop button to halt the titanium boat motion in case of a jam or other problem. Once this button is pressed it is necessary to restart the Galil motor (see Galil instruction manuals).
• Do not attempt to work on the system while a measurement is in progress.
• Do not lean over or onto the track. During disassembly (for example, to replace a NaI(Tl) detector), it may be necessary to stand on parts of the track; do not do this unless you know where weight can be placed!
• Do not place anything but samples or standards on the boat and don’t place anything on the track as the boat will move automatically.
• Do not splash water at the base of the NGR (e.g., during mopping). Although shrouded, it is not waterproof and there are high voltage leads underneath.
• When not in use, keep radioactive standards and calibration sources in the specially designated location only. Do not use the calibration sources unless you are properly trained in radioisotope safety.

         Important! Do not keep the calibration source disks on your person! They are small and could be placed in a pocket; do not do this!

• This analytical system does not require personal protective equipment.
• Visually inspect the instrument before operation for exposed electronic cable wires or unusual parts alignment.
• Keep radiation sources in the designated place.
• Do not use any other radiation sources other than those described in this document, especially open sources (e.g., dissolved europium standard or powdered U ore).

Environmental Hazards

• Keep radiation sources in the designated place.
• Do not use any other radiation sources other than those described in this document, especially open sources (e.g., dissolved europium standard or powdered U ore).
  
  

Maintenance/Troubleshooting

Common Issues

Scheduled Maintenance

• Daily: keep barcode scanner and laser windows clean by wiping with a Kimwipe. If necessary, use isopropyl alcohol to remove soil.
• As needed: ensure that acrylic tube inside NGR stays clean and dry at all times. Keep the titanium boat free of dirt and moisture as well.
• Monthly or as needed: clean the air filters on the NGR electronics crates.
• Semiannually open the NSK face plate and lubricate ballscrew.
• Annually or as needed:
  • Examine the cable management system for abraded cables or other indications of wear.
  • Remove electronics shroud at the base of the NGR and carefully clean underneath.

Related Documentation and Links

• Blum, P., 1997. Physical properties handbook. ODP Tech. Note, 26. doi:10.2973/odp.tn.26.1997
• Servo motor data sheet: blm_n23.pdf
• “A New Natural Gamma Radiation Measurement System for Marine Sediment and Rock Analysis”, Vasiliev, M.A., et al. Journal of Applied Geophysics, 75, 2011, 455-463.
• “Assessment and Use of NGR Instrumentation on the JOIDES Resolution to Quantify U, Th, and K Concentrations in Marine sediment”, Dunlea, A., Murray,R.W., Harris, R.N., Vasiliev, M., Evans, H., Spivack, A.J., and D’Hondt S., Scientific Drilling No.15, March 2013, 57-63.