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More information about the paleomagnetic standards is found at Paleomagnetic Standards.

QAQC with the SRM

Measuring an empty section tray

During the course of an expedition, routine shipboard analyses include the measurement of the natural remanent magnetization (NRM) and its alternating-field (AF) demagnetization of ARCHIVE section halves with the SRM. Because marine sediments can be poorly magnetized, it is important to have an accurate and reliable background value of the SRM with a noise level as low as it is possible to achieve with the ship conditions.

Determining the noise level is fairly easy for the SRM:. Please follow the steps below to measure an empty section tray as part of the QAQC SOP, Recent expeditions have used the "A" section tray (Figure 1).
 
1) Clean the tray physically: Remove dirt, e.g., vacuum, Windex and wipe down the tray (Figure 1).
 
2) Clean the tray magnetically: Demagnetize the tray, typically using a field comparable or slightly higher than the highest field you plan to use on real samples. Something like . Generally, archive section halves are not AF demagnetized at a field higher than 30 mT. Therefore, a magnetic cleaning of about 50 mT is good enough. Up to 80 mT may be necessary; in general, try not to push the AF unit to its maxmaximum as it damages the coils.
 
3) Measure the tray: Use the same settings (i.e., interval and background interval, leader/trailer distance, measurement speed) that you plan to use on the samples that are to be measured. Make sure the measurement does not have any flux jumps or other anomalous features. If it does, remeasure.
 
4) Measure an the empty section tray . David tells me that if you call the empty tray “BLANK”, it will as an archive section. In IMS, select "START", choose "APC/XCB Archive". In the "Manual" tab, enter manually the SAMPLE ID (e.g., "EMPTY TRAY", "BLANK TRAY", "BLANK"), the LIMS ID must be "BLANK" in order to be uploaded as a QC standard . He will then be able to have QC LIVE templates created to show the intensities, moments, inclinations, declinations, … of the BLANKs over time. I have not used QC LIVE, so I don’t know the details of thisin QCViewer. Set the section tray length at 155 cm, and then click "USE ME" (Figure 2).
 
5) Assuming that the tray measurement was accurate and valid (no flux jumps), and the BLANK measurement was similarly accurate, the X, Y, and Z moments for the BLANK sample should be zero once the drift and tray (background) corrections are made; referred to as DBC= drift and background corrected in the data files (farther right columns). Of course, they are not zero, they are instead some (hopefully) very small number, which is the noise level. 
 
An example of this measurement is shown below (Figure 3). If the magnetometer is working well and the noise level is where it is suppose to be, the moments with the background and tray correction should be <5E-10 A m^2.  Below is the text that goes with the figure, which is Am² from the SRM-Assessment report from Shanghai .below (Shangai SRM Assessment):
… the background correction is less than 5 x 10^-10 Am² at the knot and less than 2 x 10^-10 Am² elsewhere (Figure 7). For a typical core section, a moment noise level of 2 x 10^-10 Am² would equate to being able to measure split-core samples with intensities >1.5 x 10^-6 A/m or discrete samples with intensities >2.5 x 10^-5 A/m. This noise level is nearly identical to that which could be attained with the old SRM, e.g., see the Paleomagnetism Explanatory Notes for Leg 206 (Shipboard Scientific Party, 2003). 

Image Added

Figure 3. Example of blank measurement for an empty section tray after drift and background correction, Note that the moments on the three axes are very small number.

Measuring discrete samples

All discrete samples should be measured in the SRM as if they were collected from a WORKING half. The Text_ID of the standards are associated to a working half section. BE AWARE: the standards made by Scripps are oriented as if they were taken from an ARCHIVE half. Make sure to put the Scripps samples (IODPSTD01 to IODPSTD12) in the discrete tray in the right position: upside-down in the position WTA, top away (arrow of the cube away from the SRM) and +X down (Figure XX). 

QAQC with the JR6

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