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Menlo Park Laboratory:
- Superconducting rock magnetometer. This instrument
measures the remanent magnetic moment vector of specimens up
to 20 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 field to 1% of its normal value, thereby
reducing measurement time and minimizing contamination from stray
magnetic fields. Typical measurement time per sample is 2 minutes;
data are logged and reduced by online microcomputer.
- Spinner magnetometers. The laboratory maintains a
shielded flux-gate magnetometer for high-sensitvity work and
a high- speed spinner with coil detector for strongly magnetized
materials. The flux-gate instrument, equipped with digital data
logging and reduction, has a practical sensitivity of 5 x 10-7
emu. Typical measurement time per sample is 6 minutes.
- Demagnetization equipment: Alternating field and thermal
methods The AF unit operates at 400 Hz, producing a maximum magnetic
field strength of 1000 Gauss (0.1 Tesla). The sample is held
in a reciprocating tumbler to reduce spurious magnetization induced
by AF treatment. Thermal demagnetization is carried out in a
shielded furnace (internal magnetic field less than 5 x 10-5
Gauss) which holds up to 40 standard specimens per 4-hour heating/cooling
cycle. Heatings are conducted in air atmosphere. Both demagnetization
devices are housed in the shielded room near the cryogenic magnetometer,
minimizing contamination from stray magnetic fields during transport
between devices.
- Paleointensity apparatus Thellier experiments, that
determine the strength of ancient magnetizing fields, are carried
out in a system of six furnaces; each can apply a set axial magnetic
field or can be run in a near-zero field. Ambient field reduction
is supplied by a Rubins coil array with automatic feedback to
keep the working-area field below 1 x 10-4 Gauss. The furnaces
can be operated in vacuum or in an inert atmosphere (argon or
nitrogen) to inhibit oxidation of the specimens. Up to 30 specimens
can be loaded in the system per heating/cooling cycle.
- Curie balance Strong-field magnetization and Curie temperatures
are measured in this electromagnet/balance system. The specimen
(typically 0.5-1.0 gram; solid or granular) is suspended between
the electromagnet pole pieces which produce a magnetic gradient
force on the specimen. A balance automatically records apparent
weight, which is proportional to magnetization, as the specimen
is heated. Heatings can be performed in air, vacuum, or inert
gas. The electromagnet field limit is 8000 Gauss (0.8 Tesla).
The furnace and magnet are controlled automatically, and the
magnetization/temperature data are recorded digitally. A complete
heating/cooling cycle up to 700 degrees C runs in 2.25 hours.
Strong-field magnetization curves can be run manually, giving
values of saturation magnetization.
- Electromagnet Isothermal remanent magnetization is
imparted to the specimen at room temperature with an electromagnet,
capable of producing DC fields up to 7000 Gauss (0.7 Tesla).
Magnetic remanence is then measured with one of the magnetometers.
Saturation remanent magnetization and coercivity of remanence
are measured with this system.
- Susceptibility meter Low-field magnetic susceptibility
is measured with a Sapphire SI-2 system. The system accommodates
specimens up to 20 cc in volume; a larger pass- through detector
is also available for use with long sediment cores up to 10 cm
in diameter. Bulk susceptibility and anisotropy of susceptibility
can be measured. The data are recorded and reduced automatically
by an online microcomputer.
- Rock drills and other field equipment. The laboratory
maintains a full complement of portable rock drills, sample orienting
equipment, and sediment sampling tools.
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