Author(s): | M. Hastedt, M. Vasilyev, Y. Vasilyeva |
Revised by: | Exp376 Techs |
Reviewer(s): | D. Houpt |
Supervisor Approval (Name, Title, Date): | draft Exp. 362T (July 2016) |
Audience: | Marine Laboratory Specialists |
Origination date: | 4/28/08 |
Current version: | 376 |
Revised: | V1.3 | 7/5/2017 (IODP-II); 372 | 03/02/2018 ; 374; 375:376 |
Domain: | Physics |
System: | Natural Gamma Radiation Logger |
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.
Concentrations of uranium, thorium and potassium in geological materials provide insight into many important lithological characteristics and geologic processes. In marine sediment, they can aid in identifying clay compositions, depositional environments, and diagenetic processes. In hard rock, they can yield information about the alteration and heat production of rocks (Dunlea et al., 2013). A high-efficiency, low-background system for the measurement of natural gamma radioactivity in marine sediment and rock cores designed and built by the JRSO at Texas A&M University is used aboard the JOIDES Resolution.
Electromagnetic gamma rays are emitted spontaneously from an atomic nucleus during radioactive decay. Each nuclear isotope emits gamma rays of one or more specific energies. NGR data are reported in total counts per second, a quantity dependent on instrument and core volume, derived from the integration of all counts over the photon energy range between 0 and ~3.0 MeV. Total counts represents the combined contributions by K, U, and Th, matrix density resulting from Compton scattering, and matrix lithology resulting from photoelectric absorption. Data generated from this instrument are used to augment geologic interpretations.
The NGR Logger consists of eight Sodium Iodide (Thallium) (NaI(Tl)) detectors surrounded by both passive and active shielding. The measurement of natural radioactivity from core samples faces the challenge of overcoming background noise, which consists of environmental radioactivity and cosmic radiation. In order to protect measurements from environmental noise the NGR system includes several layers of lead, which act as a passive shield. However, lead shielding is not enough to eliminate enough of the incoming cosmic radiation to measure low-count cores. To reduce the cosmic background further the NGR has a layer of active shielding consisting of plastic scintillator detectors and nuclear electronics. There are five plastic scintillators on the top of chamber and an additional plastic scintillator inside each NGR door. For rejection of counts in NaI(Tl) detectors associated with cosmic rays, fast–slow coincidence logic was implemented. In the event of coincidence within a 400-500 ns window between signals from the fast outputs of NaI(Tl) detectors and any of the seven plastic scintillators, a VETO signal is generated on the gate input of the multichannel analyzer modules (MCAs) and further readout of such an event is rejected.
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 entered. The boat stops at position #1, where the top of the boat is centered above 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 and begins counting at position #2. When the run completes, the section returns to the starting position and can be unloaded.
NGR analysis results are expressed as spectra (counts vs keV energy) for each measurement and the raw spectra are saved in a zip folder in the database. The spectra are reduced by the NGRL software and produce total counts per second (cps), adjusted for energy threshold (>100 keV), edge corrections, and background radiation.
Energies below 100 keV (and into the X-ray portion of the spectrum) are not recorded, as the NGRL has not been designed to characterize the natural radioactivity below this level.
The NGRL system consists of five major units (Fig. 1):
Figure 1. NGR logger system components.
The support frame holds the NGRL components, including the heavy lead layers of the passive shield. It is constructed of steel that is welded to the support rails distributing the 5 tons of weight evenly on the deck, preventing it from shifting in heavy seas.
A steel I-beam frame above the chamber allows for transportation of heavy components during any assembly/disassembly activities or for opening the doors by using the chain hoist.
Note: Both NGRL doors contain plastic detectors inside and two PMT units beneath each detector. These are very fragile and care must be taken not to damage them while moving the doors!
Currently on the ship the NGRL operates with door #1 fixed in the open position. Door #2 (back door) stays closed. Open door #2 to place the standard over detector #8, as the standard will need to be positioned past the normal stop position.
The main NGR detector unit consists of the following (Fig. 2, Fig. 3):
The NaI(Tl) detectors are covered by at least 8 cm of lead shielding. In addition, lead separators (~7 cm of low-background lead) are positioned between the NaI(Tl) detectors. The innermost 4 cm of the lead shielding is low-background lead, while the outer 4 cm is composed of virgin lead. The inherent radioactivity of the virgin lead is such low energy that the inner 4 cm of low-background lead shields nearly 100% of it. The internal radioactive rates of the lead shields are:
The NaI(Tl) detectors are housed in stainless steel and hermetically sealed against atmospheric moisture. The sodium iodide crystals are extremely hygroscopic if moisture gets inside the housing they can lose their optical properties. For this reason, it is vitally important that the detector housings be protected from corrosion. Each detector is a half-ring of 10 cm thick x 10 cm wide NaI(Tl); the shape is to maximize the efficiency of capturing gamma rays emitted from whole-round core sections. Each detector has its own photomultiplier tube (PMT).
In addition to passive lead shielding, the NGR employs plastic scintillators to suppress the high-energy gamma and muon components of cosmic radiation by producing a VETO signal when charged particles from cosmic radiation pass through the plastic scintillators:
Each plastic detector has two PMTs to maximize light collection across a somewhat large detector surface.
Signal processing from all PMTs is organized through standard NIM electronics modules. The photomultipliers are located beneath the detectors, 1 for each NaI(Tl) detector and 2 on each door and shell-shaped plastic detector.
Figure 2. NGR detector system schematic.
Figure 3. Internal view of NGR logger showing NaI(TI) and plastic scintillator detectors and lead shielding
It should be noted that a professional nuclear electronics engineer has tuned the NGR electronics. As has been observed through years of operation, the NGR electronics show steady performance and there is usually no need to work with any of the electronic settings, except for voltage tuning in the calibration procedure. In all other cases, call an appropriate person with sufficient training in the NGR electronics before attempting to adjust any of the electronics settings.
The NGR electronics crates (Fig. 4) include:
Figure 4. Electronics crate.
The coincidence logic NIM bin (left side) consists of the plastic signal flow units (Fig. 5, A through E), coincidence determination units (F and G), NaI(Tl) signal flow units (H through J), a summary coincidence unit (K), and an ORTEC 480 pulser. For a detailed description of the electronics bin, please see the NGR logger academy MS Power Point presentation.
Figure 5. Coincidence Logic NIM Bin
The spectrometric logic NIM bin (right side) consists of NaI(Tl) signal processing unit (Fig. 6), which is eight paired sets of ORTEC 855 amplifiers and ORTEC 927 APSEC multichannel analyzers (MCA).
Figure 6. NaI(Tl) spectrometric processing unit
The signal summary monitoring panel is a CAEN Quad Scaler and Preset Counter Timer (model N.1145) (Fig. 7).
Note: that while the Galil motor is running, the counts may be very high due to radio frequency (RF) interference from the motor. During analysis, the motors are turned off to prevent this noise from affecting the measurement.
Figure 7. CAEN signal counter depicting summed plastic, NaI(Tl), and coincidence values
The electronics crate also contains the ISEG power supply for the plastic detectors, the PC, and various communications electronics (e.g., USB hubs and cables), not pictured.
The core delivery system consists of the Galil control panel and Galil servo motor assembly, the NSK actuator, Delrin rails, the titanium core boat, and electronic limit switches.
The Track Utility on the main NGRL Core Analyzer window is used to control of the boat position. There are three basic positions of the boat inside NGR chamber:
The Track Utility display also provides a Home position (loading position) as well as manual fine controls.
The PC is used solely for running the NGRL and reviewing data. It must never be connected to the internet or any devices which may interfere with the proper functioning of the instrument and its software. Users should also avoid using the PC for any other purpose while a measurement is running.
The APC UPS units provide a short window of normal operation (a few hours at most) if ship’s power is down. If ship’s power is not going to be restored quickly, the technician should shut down the NGRL following the shutdown procedure.
The track control and interface to data acquisition software (Maestro 32 by ORTEC) is a LabVIEW application. The Main Control Panel provides access to the main data acquisition functions and utilities as well as:
In addition to LabVIEW (and Maestro if one is performing calibration), the uploader software “MUT” is installed on the NGRL PC. MUT will upload the NGR raw and reduced data into the LIMS.
Inexperienced operators should only the LabVIEW application and MUT. Maestro has many features and controls and can alter the detectors’ settings and care should be taken when using it.
The titanium core boat has a 3.5 cm diameter with welded ends, attached to a Delrin rod that connects it to the NSK actuator. The inherent radioactivity of the boat and the rod are very low and do not affect core measurement.
The activity of the epoxy and plaster cores is extremely low—significantly lower than background levels—and can be handled safely even for extended periods of time. The disk-shaped sources are 1 µCi nominal activity and should be handled only by properly trained operators. They do not represent a short-term hazard, but long-term exposure would be harmful.
Do not switch off the power supply when it is not necessary!
Utilizing standard NIM modules and electronics crates, the NGRL detectors/electronics are designed to run uninterrupted for years at a time. Switching the power supply off/on is one of the worst operations for the instrument! Do it only if it is necessary!
Partial (see Partial Shutdown) or complete (see Full Shutdown) shutdown may become necessary in the following conditions:
Figure 8, below, shows the location of the main power switch and the two NIM 4001B crate power switches.
Figure 8. Power switch placement
Figure 9a. iSEG Hard ware Setup and Main screen
Figure 9b. The controller cards may be the EHS or EHQ model and are labeled accordingly.
Figure 10. Program termination query.
Figure 11a. iSEG Multi-Channel High-Voltage Modules; Ch00.
Figure 11b. iSEG Multi-Channel High-Voltage Modules; Ch01.
Figure 12. Electronics Crate: Shutdown.
Turn off the master power switch above the middle NIM rack (blue circle in Fig. 13The fans are connected to the uninterruptable power supply (UPS) and must be unplugged to turn off.
Figure 13. Master Power Switch.
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:
Figure 14. iSEG Hard ware Setup and Main screen. The controller cards may be the EHS or EHQ model and are labeled accordingly.
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
Figure 16. Typical background file acquisition parameters in NGR configuration dialog window; note background acquire time should be 21,000 seconds, not 20,000.
Even uncalibrated, the NGRL will still produce and record signals, but significant error will arise.
The multichannel analyzer (MCA) collects the analog signal from the PMT and divides it into channels, but without energy calibration, it is impossible to characterize the energy into scientific units (i.e., MeV). Radioactive materials of known energy are placed within the NGRL at specific locations and the ORTEC Maestro program is used to ensure that the signals from the standards lie in their proper channels.
In addition, it is necessary to calibrate the instrument in the time domain. If this is not done, the active shielding will not function properly without proper timing of the anti-coincidence logic. This will decrease the effectiveness of the active shielding.
Make sure to update the NGR’s NGR_configuration/Folders_and_Files dialog window with the correct location of the most recent calibration files. Update the configuration files after you have completed the calibration procedure.
Warning! The radioactive sources (kept in a black lockbox located in cabinet PPTRKF 13) generate a relatively small amount of radiation, but the user should take care to minimize interaction with them. The sources should be returned to the radioactive standards lockbox as soon as the procedure is finished.
Note: The 60Co source has a much shorter half-life than the 137Cs source as stated above. Getting low 60Co peaks probably does not mean a problem with the instrument: check the date of the standard disk first and determine if the remaining activity seems reasonable compared to past experiments. When new, the 60Co double peak is roughly the same size as the 137Cs single peak; as the sources age, the 60Co double peak will shrink relative to the 137Cs peak.
Figure 17. Aluminum Calibration Core.
Figure 18. Calibration Source Holder.
Figure 21. Maestro MCB Properties dialog window.
Figure 22. Detectors #7 and #8 after acquiring signal from the 137Cs and 60Co sources; the lower window, detector #8.
Figure 23. Calibrate dialog window to set a peak’s energy
If the normal energy calibration procedure does not bring the 137Cs peak (662 keV) close to channel #226, then it may be necessary to tune the NGRL’s detector voltage and then repeat the calibration procedure. This is done detector-by-detector as noted below.
Warning! This procedure may be necessary at the start of any expedition as a response to drift, but should not be undertaken without clearly understanding the process.
The total number of channels in the high voltage divider of the MCA is 1024. The 137Cs decay has a peak of 662 keV and the two 60Co peaks are 1173.2 and 1332.5 keV, respectively. Normally the 662 keV 137Cs peak appears close to channel #226, however this will drift over time with a different drift rate for each detector. By changing the voltage in the bias adjustment box (Fig. 24), the operator can control the position of a given peak and bring it to (or close to) the appropriate channel. If the 137Cs peak is not within a few channels of #226, it may be necessary to use the adjustment box to adjust the peak. Using the Maestro program, the operator can see the position of the peak from the sources and make adjustments. The potentiometers in the bias adjustment box are very sensitive and nonlinear, so only a lite touch to avoid moving the peak too far.
Figure 24. NaI(Tl) bias adjustment box
The gross voltage of the PMT should be in the range of 650 to 750 volts; the leads for the bias adjustment box have been stepped down to the equivalent in millivolts, so a voltmeter can be used without the presence of dangerous voltages. Thus, the voltmeter should display a value somewhere between 650 and 750 mV. Each detector has a positive (red) lead; they share a common ground (white) lead. The row of silver screws above the numbers are the potentiometers.
Figure 25. Maestro window showing the 137Cs and two 60Co peaks.
Figure 26. Zoomed-in Maestro window of the 137Cs peak, showing that the peak is at channel 226.
Step-by-step procedure for setting the NaI(Tl) detector bias voltage:
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.
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.
Figure 27. Insert the multimeter probes into the bias detector box to measure the voltage. Black to white. Red to red
| NGRL Bias Voltage Calibration Worksheet | ||||||||
|---|---|---|---|---|---|---|---|---|
| Technician: __________________________________ Exp: ___________Date:____________________________ | ||||||||
NaI det # | channel corresponding to keV reading before calibration | channel corresponding to keV reading after calibration | ||||||
multi- meter reading |
137 Cs Peak keV Channel | 60Co channels |
multi- meter reading |
137 Cs Peak keV Channel | 60Co channels | |||
1170 keV |
1330 keV |
1170 keV |
1330 keV | |||||
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Table 1. NGRL NaI(Tl) Detector Bias Voltage Table
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.
The pulsers are not necessary unless the user wishes to see a sharply-defined channel marker to facilitate adjustments. The user can complete the energy calibration without using either type of pulser.
After all eight detectors are calibrated; Maestro shows energy-corrected results. Core spectra from these detectors display both channel and energy information. The ASCII files with the calibration coefficients are saved and available for the data reduction software. The operator should evaluate the position of the K peak (1.460 MeV) in core samples to ensure the calibration has been recorded with reasonable results. (Known U and Th peaks can be used for this purpose as well.)
When the 137Cs peak is calibrated to channel 226±2, the 40K peak should fall roughly at channel 498±4, in the same direction of error as the 40K peak because energy vs. channel is quite linear.
(If the 137Cs peak is found at channel 224, the 40K peak is likely to lie at or about channel 494; if the 137Cs peak is found at channel 228, the 40K peak is likely to lie at or about channel 502.)
The system is now calibrated sufficiently to perform analysis on a total counts basis. Further calibration with known values of K, U, and Th (KUT) must be performed before KUT abundance can be determined. The scientist must do this reduction for KUT from the spectral data and no automated process exists for this.
The above procedure presupposes the calibration sources are positioned exactly in the center of the lead separator between each NaI(Tl) detector and on the top of the aluminum standard holder. Any significant error in this positioning (especially if the source is too close vertically to the detector) will introduce systematic errors in the calibration, as the lead shielding will interact with the gamma rays differentially between the two detectors. Systematic errors can be controlled by making measurements placed from both the right and left of detectors #2 through #7. (It is physically impossible to make this determination for detectors 1 and 8 but we can use the systematic error determined from the other six detectors to estimate the error for these detectors.) Calibrations done with manual positioning demonstrate that peak position can shift up to 5–6 channels (~15–18 keV) with a typical value of 2–3 channels (~6–10 keV). It is therefore important that the sources be placed precisely (the normal procedure does this).
If you are performing time calibration, different holders and positioning are used; refer to that section for details.
Note: that the NGRL software does not produce “KUT” data. The spectral data (found in the ZIP file produced by the NGRL software) is there, but significant post-acquisition work (beyond the scope of the IODP marine technician’s duties) is needed to derive it.
The raw spectrum recorded in the file contains the spectral information to identify the 40K line and the several 232Th and 238U lines. In order to use this information to produce calibrated % K and ppm Th and U, it is necessary to measure the intensity of the related peaks from standards of known activity. (It is also necessary to have a good enough quality spectrum, which for geologic cores with low activity (<10-15 cps) may require longer read times as well as additional calibration.)
Aboard the JOIDES Resolution, a number epoxy core sections containing K and Th salts are available with different levels of activity.
Note! Even if the epoxy core label indicates that it contains U, it does not; the manufacturer inadvertently omitted the radioisotope!
Two gypsum plaster core sections are available with known concentrations of U salt as well. As stated elsewhere, the epoxy and plaster cores’ activities are so low that they can be considered effectively non-radioactive for handling purposes.
In order to perform a KUT study, each detector must be calibrated against the standards, which in turn requires that the core section be centered over each detector. Do not try to use one epoxy or plaster core to cover more than one detector, although it is possible to position multiple standards over different detectors simultaneously.
Collect spectra for the standards, from each detector, for at least 30 minutes (preferably 2-4 hours) to acquire a high-quality spectrum. For good quantitation, it is necessary to have individual radioisotope peaks on the order of 2000 counts (each).
Note that in order to position the standard core sections over detector #8, the rear door must be opened with the chain hoist and the plug at the end of the acrylic tube removed.
40K decay produces only a single peak within the NGRL’s sensitivity range, and presuming 238U concentration is not high, evaluation of the 40K peak is relatively straightforward. High 238U concentration creates a “shoulder” peak on the 40K peak and must be deconvoluted from the potassium signal to produce the correct 40K concentration.
232Th and 238U decay produces a large number of gamma-ray peaks, making quantification much more challenging. For reference, a decay isotope diagram for the Th and U chains are provided here (Fig. 28 and 29).
It is beyond the scope of this manual to describe the full analytical procedure. Dunlea et al. (2013) provides some guidance on this matter.
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
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 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.
This section gives instructions for running whole-core sections through the NGR system.
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:
Figure 30. NGRL Core Analyzer Screen, Ready to Start Scan.
Figure 31. Core Analyzer Screen Showing Histogram.
Figure 32. Core Analyzer Screen in Binned Mode Display.
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!
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:
The LIMS components for the NGR analysis are as follows:
Component Name |
Reported Name |
Units | Result Type (N = numeric, T = text) |
Description |
total_counts_per_sec | NGR total counts | cps | N | Rate of natural gamma radiation across the spectrum of ~0.1-3.0 MeV for a 10 cm section of core |
absolute_error | Error | cps | N | Inverse of the square root of total counts |
relative_error | Error (%) | none | N | Relative error of the measurement, defined as the absolute error divided by the number of counts, expressed as a percentage |
period | Measurement period | sec | N | Length of Live time for the NGR measurement (usually 300 sec) |
detector | NGR detector number | none | N | NaI(Tl) detector number, from 1 to 8 |
offset | Offset | cm | N | Location of measurement from top of section |
observed_length | Observed length | cm | N | Length of section as observed by NGR operator |
comments | Comment | none | T | Comment on the measurement, entered on sample entry screen |
archive_asman_id | Archive ASMAN ID | none | N | ASMAN database ID number for archived file folder |
archive_filename | Archive filename | none | T | ASMAN database filename for archived file folder |
summary_asman_id | Summary ASMAN ID | none | N | ASMAN database ID number for summary file |
summary_asman_id | Summary filename | none | T | ASMAN database filename for summary file |
run_asman_id | Run ASMAN ID | none | N | ASMAN database ID number for run file (logger data output file) |
run_asman_id | Run filename | none | T | ASMAN database filename for run file (logger data output file) |
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.
NGR operational safety guidelines were developed with regard to automatic equipment operation, laser and radiation sources, high voltage electronics, and general laboratory procedures.
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!
Issue | Possible Causes | Solution |
Galil motor error | Red emergency stop button pressed | Resolve reason for emergency stop. Release emergency stop button. Open Galil control software and perform the following commands at the text prompt: MO SH This should clear the Galil amplifier error and allow the user to use the NGR software to find home and then continue work |
Amplifier overcurrent | Usually means a safety has been tripped and can be cleared the same way as the emergency stop button. Can, however, mean that that amplifier is damaged and must be replaced. Call an ET
If core is still inside the NGR chamber and the motor cannot be returned to service, follow these steps:
| |
No plastic or coincidence signal on CAEN counter | ISEG power unit fault or user inadvertently answered “yes” to the exit prompt | Open ISEG control software and follow startup procedure in this user guide. Look for error states; if not, continue measurements |
Low plastic count values on CAEN counter | ISEG channel failure on one or more channels | Open ISEG control software and check voltage and current levels to identify if a scintillator is “dark.” Move leads to open channels (default extra channel is #0) and document which channel is which detector (the door PMTs have a different voltage requirement than the hoop PMTs). |
No NaI(Tl) signal on CAEN counter | ORTEC modules have lost power | Call an ET |
High NaI(Tl) counts on CAEN counter | Internal contamination | Clean acrylic tube |
Short in a PMT base | Isolate which detector is causing the noise. This can be done by removing the MCA input lead one by one until the NaI(Tl) CAEN counts return to normal, or by running a core experiment and observing which detector takes too long to complete. That is the one with noise.
Real time = Live time + Dead time
Electrical noise causes more dead time, lengthening the measurement (real) time.
Corrective action may include checking the BNC cables and the PMT base underneath the NGR chamber (call an ET!) | |
NSK actuator (big silver actuator) sticks | Too long since the last lubrication | Open the NSK face plate and lubricate with the appropriate lubricant (ONLY!). Replacing the face plate can be tedious and it helps to do it with someone who has done it before |
Cooling fan making a lot of noise | Bad bearing on a fan motor | Call an ET to replace or clean fan |
