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GMEG - Geophysics Unit of Menlo Park, CA- (GUMP)


Geophysics Unit of Menlo Park, CA (GUMP)

U.S. Geological Survey - Western Region - Geology and Geophysics

USGS Rock- and Paleo-magnetics Laboratory

Cryogenic Magnetometer

Superconducting Rock Magnetometer with Automated Sample Changer

Superconducting Rock Magnetometer with Automated Sample Changer:  This instrument measures the remanent magnetic moment of rock specimens up to 10 cc in volume with a practical sensitivity from 1 emu to 5 x 10-8 emu.  The magnetometer is housed in a shielded room that reduces the ambient magnetic field to less than one percent of its normal value, thereby reducing measurement time and minimizing contamination from stray fields.  In 2008, the magnetometer system underwent a major upgrade with the installation of an automated sample changer that greatly enhances the throughput of the instrument.  The changer, which accommodates up to 180 rock specimens per load, allows unattended operation of the magnetometer as it performs alternating-field demagnetization and various rock-magnetism experiments (IRM, ARM, magnetic susceptibility, RRM).  Credit for the design and fabrication of the changer goes to Prof. Joe Kirschvink (Caltech) and members of RAPID (Rock- and Paleo-magnetic Instrument Development), a consortium of paleomagnetists in academia and government.  During a typical measurement sequence, the rock specimen is moved by a snake-train of cups, picked up by a quartz tube under vacuum, and inserted into a coil assembly above the magnetometer access bore.  An orthogonal pair of coils (vertical and horizontal) can apply alternating fields for demagnetization or a DC pulse for acquisition of isothermal remanent magnetization (IRM).  In addition, magnetic susceptibility can be measured and small DC fields can be applied for anhysteretic remanent magnetization experiments (ARM).  Remanent magnetization is measured by lowering the specimen into the 3-axis SQUID-sensor region, about 75 cm below the coil assembly.  When the specimen measurements are complete, the quartz rod retracts the specimen from the magnetometer bore. The snake-train then moves to receive the finished specimen and to bring the next specimen to a position above the magnetometer access.  Progress of the unattended operation is monitored via an internet camera, and the system also sends email alerts to the researcher’s desk top.


***See photos of our new automated sample handling system***

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