Magnetic susceptibility is the degree of magnetism of a material in response to an applied magnetic field. If the magnetic susceptibility is positive, the material can be paramagnetic, ferromagnetic or antiferromagnetic. In these cases the magnetic field is strengthened by the presence of the material. Alternatively, if the magnetic susceptibility is negative, the material is diamagnetic and as a result, the magnetic field is weakened by the presence of the material.
MS2C Loop and MS2E Point Magnetic Susceptibility Sensors
Two sensors are available from Bartington Instruments (Bartington) for integration with a Geotek MSCL system, a loop sensor (MS2C) and a point sensor (MS2E) that are paired to the Bartington MS3 meter with a measuring range of 26 SI.
The Bartington loop sensor (MS2C) is used for volume susceptibility measurements of whole sediment and rock cores. It is available in a range of internal diameters from 30 mm to 150 mm. The Bartington point sensor (MS2E) is used for surface scanning and providing high-resolution surface measurements on split sediment or slabbed rock cores.
An oscillator circuit in the sensor produces a low intensity of approximately 80 ampere per meter (A/m) root mean squared (RMS) non-saturating, alternating magnetic field (0.565 kHz for the MS2C sensor and 2 kHz for the MS2E sensor). Any material in the near vicinity of the sensor that has a magnetic susceptibility will cause a change in the oscillator frequency. The Geotek MSCL system electronics convert this pulsed frequency information into magnetic susceptibility values reported as SI or CGS.
Sensor Calibration and Data Processing
The MS2C and MS2E sensors are electronically calibrated to measure a single standard of stable iron oxide tested and analysed by Bartington. All magnetic susceptibility sensors are supplied with a stable iron check piece, which can be used to check the long-term consistency of the calibration.
The data acquired using the MS2C and MS2E sensors can be presented as uncorrected, volume specific magnetic susceptibility, corrected volume specific magnetic susceptibility or mass specific magnetic susceptibility.
Alterations in the magnetic susceptibility within core samples are often stratigraphic. Therefore magnetic susceptibility records are an excellent core to core correlation tool. In addition, the tool can be used to determine the lithological properties as well as any changes in sediment provenance and/or diagenetic environment. Magnetic susceptibility measurements can be used as proxy for permeability measurements, and in the mining industry the susceptibility of the core material can be used to determine the occurrence of volcanics and to feed into magnetic anomaly models for geophysical surveys.