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137:. These magnetometers can be moderately sensitive if several tens of watts are available to power the aligning process. If measurements are taken once per second, standard deviations in the readings is in the 0.01 nT to 0.1 nT range, and variations of about 0.1 nT can be detected.
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and excavated more than 7,000 square feet (650 m) to match anomalous magnetometer readings with the archaeological features that produced them. This was the first systematic use of a proton magnetometer for archaeological research in North
America.
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The main sources of measurement errors are magnetic impurities in the sensor, errors in the measurement of the frequency and ferrous material on the operator and the instruments, as well as rotation of the sensor as a measurement is taken.
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Portable instruments are also limited by sensor volume (weight) and power consumption. PPMs work in field gradients up to 3,000 nT m which is adequate from most mineral exploration work. For higher gradient tolerance such as mapping
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For hand/backpack carried units, PPM sample rates are typically limited to less than one sample per second. Measurements are typically taken with the sensor held at fixed locations at approximately 10 meter increments.
122:, and is equal to 0.042576 Hz nT. Because the precession frequency depends only on atomic constants and the strength of the ambient magnetic field, the accuracy of this type of
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of fired clays, and differences in the magnetic susceptibility of disturbed soils. During 1961–1963, they surveyed more than 100,000 square feet (9,300 m) of the
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are popular; water can also be used), causing some of the protons to align with that field. The current is then interrupted, and as protons realign themselves with the
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at a frequency that is directly proportional to the magnetic field. This produces a weak rotating magnetic field that is picked up by a (sometimes separate) inductor,
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Smekalova T. N., Voss O., Smekalov S. L. "Magnetic
Surveying in Archaeology: More than 10 years of using the Overhauser GSM-19 gradiometer", Wormianum, 2008.
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electronically, and fed to a digital frequency counter whose output is typically scaled and displayed directly as field strength or output as digital data.
169:(UK) Archaeometric Laboratory, used proton magnetometers to locate and map buried archaeological features, including iron objects in the soil,
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and detecting large ferrous objects
Overhauser magnetometers can handle 10,000 nT m and Caesium magnetometers can handle 30,000 nT m.
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Johnston, R. B., "Proton
Magnetometry and its Application to Archaeology: An Evaluation at Angel Site", Indiana Historical Society,
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The frequency of Earth's field NMR for protons varies between approximately 900 Hz near the equator to 4.2 kHz near the
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The relationship between the frequency of the induced current and the strength of the magnetic field is called the
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to map the positions of demolished walls and buildings, and at sea to locate wrecked ships, sometimes for
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228:. Glenn Black Laboratory of Archaeology and The Trustees of Indiana University. Archived from
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PPMs were once widely used in mineral exploration. They have largely been superseded by
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Black, G. A. and
Johnston, R. B., "A Test of Magnetometry as an Aid to Archaeology",
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Instrument which measures very small variations in the Earth's magnetic field
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77:) or helium magnetometers, which sample faster and are more sensitive.
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Requirements for obtaining high accuracy with proton magnetometers
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In 1958 Glenn A. Black and Eli Lilly, following the work of
266:, 2 vols., Indiana Historical Society, Indianapolis, 1967.
226:"Geophysics at the Angel site: Past, present and future"
271:"Applications Manual for Portable Magnetometers"
39:(EFNMR) to measure very small variations in the
8:
224:Peebles, Christopher S. (July 23, 1996).
89:creates a strong magnetic field around a
37:Earth's field nuclear magnetic resonance
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7:
157:Proton magnetometer in archaeology
14:
214:". GEM Systems Inc., 2010-01-11.
210:Dr. Ivan Hrvoic, Ph.D., P.Eng. "
175:Angel Mounds State Historic Site
85:A direct current flowing in a
67:Overhauser effect magnetometers
33:proton precession magnetometer
23:Proton magnetometer from 1967.
1:
259:, Vol. 28, pp. 199–205, 1962.
35:(PPM), uses the principle of
171:thermoremanent magnetization
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312:Indiana Historical Society
282:Prehistory Research Series
165:and his associates at the
275:originally published 1973
119:proton gyromagnetic ratio
54:It is used in land-based
302:Diving support equipment
284:, Vol. IV, No. II, 1962.
81:Principles of operation
47:objects on land and at
151:banded iron formations
41:Earth's magnetic field
24:
105:magnetic field, they
22:
69:and alkali vapour (
60:recreational diving
29:proton magnetometer
269:Breiner, Sheldon,
257:American Antiquity
31:, also known as a
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167:Oxford University
135:geomagnetic poles
51:to be detected.
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317:Magnetic devices
273:, 1999 edition,
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73:, rubidium, and
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93:-rich fluid (
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307:Geomagnetism
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234:. Retrieved
230:the original
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126:can reach 1
124:magnetometer
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56:archaeology
43:, allowing
296:Categories
198:References
111:amplified
75:potassium
236:19 March
186:See also
95:kerosine
91:hydrogen
87:solenoid
179:Indiana
107:precess
103:ambient
71:caesium
45:ferrous
99:decane
238:2014
97:and
192:NMR
177:in
128:ppm
49:sea
298::
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62:.
27:A
277:.
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