Proton magnetometer
Encyclopedia
The proton magnetometer, also known as the proton precession magnetometer (PPM), uses the principle of Earth's field nuclear magnetic resonance (EFNMR
) to measure very small variations in the Earth's magnetic field
, allowing ferrous
objects on land and at sea
to be detected.
It is used in land-based archaeology
to map the positions of demolished walls and buildings, and at sea to locate wrecked ships, sometimes for recreational diving
.
PPM's were once widely used in mineral exploration. They have largely been superseded by Overhauser Effect magnetometers and alkali vapour (cesium, helium, and potassum) magnetometers, which sample faster and are more sensitive.
The principle of operation is outlined in the magnetometer article. Other applications of PPM's are also outlined in this article.
, Indiana University
, Bloomington, Geophysics at the Angel Site: Past, Present, and Future) in 1958 Black and Mr. Eli Lilly, following the work of M. J. Aitken and his associates at the Oxford University (UK) Archaeometric Laboratory, used proton magnetometers to locate and map buried archaeological features. Magnetometers measure minute differences in the magnetic field
of the earth
caused by ferrous concentrations (and iron objects) in the soil, thermo-remnant magnetism of fired clays, and differences in the magnetic susceptibility of disturbed soils. In 1959, with the support of the Indiana Historical Society, Black rented a general purpose magnetometer. It proved a bit better than previous magnetometers for locating very large features, but was not really suited to archaeological work. In 1959, with the support of the Society, Black purchased a magnetometer built specifically for archaeological work from the Oxford
Archaeometric Laboratory".
"In 1961 and in 1963 the National Science Foundation awarded funds to Black and to the Indiana Historical Society to evaluate the magnetometer as a tool for archaeological research. During 1961-1963, more than 100000 square feet (9,290.3 m²) of the Angel site were surveyed and more than 7000 square feet (650.3 m²) were excavated, in order to match anomalous magnetometer readings with the archaeological features that produced those readings. For the most part the strategy was to locate and follow the course of the stockade trench, but other features, such as houses, fire basins, and pits, were sought and located as well. This work, which was the first systematic use of a proton magnetometer for archaeological research in North America, was reported by both Johnston and by Black".
Earth's field NMR
Nuclear magnetic resonance in the geomagnetic field is conventionally referred to as Earth's field NMR . EFNMR is a special case of low field NMR....
) to measure very small variations in the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...
, allowing ferrous
Ferrous
Ferrous , in chemistry, indicates a divalent iron compound , as opposed to ferric, which indicates a trivalent iron compound ....
objects on land and at sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
to be detected.
It is used in land-based archaeology
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
to map the positions of demolished walls and buildings, and at sea to locate wrecked ships, sometimes for recreational diving
Recreational diving
Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels...
.
PPM's were once widely used in mineral exploration. They have largely been superseded by Overhauser Effect magnetometers and alkali vapour (cesium, helium, and potassum) magnetometers, which sample faster and are more sensitive.
The principle of operation is outlined in the magnetometer article. Other applications of PPM's are also outlined in this article.
Proton magnetometer in archaeology
According to Christopher S. Peebles (Glenn A. Black Laboratory of ArchaeologyArchaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
, Indiana University
Indiana University Bloomington
Indiana University Bloomington is a public research university located in Bloomington, Indiana, in the United States. IU Bloomington is the flagship campus of the Indiana University system. Being the flagship campus, IU Bloomington is often referred to simply as IU or Indiana...
, Bloomington, Geophysics at the Angel Site: Past, Present, and Future) in 1958 Black and Mr. Eli Lilly, following the work of M. J. Aitken and his associates at the Oxford University (UK) Archaeometric Laboratory, used proton magnetometers to locate and map buried archaeological features. Magnetometers measure minute differences in the magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
of the earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
caused by ferrous concentrations (and iron objects) in the soil, thermo-remnant magnetism of fired clays, and differences in the magnetic susceptibility of disturbed soils. In 1959, with the support of the Indiana Historical Society, Black rented a general purpose magnetometer. It proved a bit better than previous magnetometers for locating very large features, but was not really suited to archaeological work. In 1959, with the support of the Society, Black purchased a magnetometer built specifically for archaeological work from the Oxford
Oxford
The city of Oxford is the county town of Oxfordshire, England. The city, made prominent by its medieval university, has a population of just under 165,000, with 153,900 living within the district boundary. It lies about 50 miles north-west of London. The rivers Cherwell and Thames run through...
Archaeometric Laboratory".
"In 1961 and in 1963 the National Science Foundation awarded funds to Black and to the Indiana Historical Society to evaluate the magnetometer as a tool for archaeological research. During 1961-1963, more than 100000 square feet (9,290.3 m²) of the Angel site were surveyed and more than 7000 square feet (650.3 m²) were excavated, in order to match anomalous magnetometer readings with the archaeological features that produced those readings. For the most part the strategy was to locate and follow the course of the stockade trench, but other features, such as houses, fire basins, and pits, were sought and located as well. This work, which was the first systematic use of a proton magnetometer for archaeological research in North America, was reported by both Johnston and by Black".
Further reading
- Black, G. A. and Johnston, R. B., "A Test of Magnetometry as an Aid to Archaeology," American Antiquity, Vol. 28, pp. 199-205, 1962.
- Black, G. A., Angel Site: An Archaeological Historical, and Ethnological Study, 2 vols., Indiana Historical Society, Indianapolis, 1967.
- Johnston, R. B., "Proton Magnetometry and its Application to Archaeology: An Evaluation at Angel Site," Indiana Historical Society, Prehistory Research Series, Vol. IV, No. II, 1962.
- Smekalova T. N., Voss O., Smekalov S. L. "Magnetic Surveying in ArchaeologyMagnetic Surveying in Archaeology (book)Magnetic Surveying in Archaeology is a book written by Russian archaeologist T. N. Smekalova together with O. Voss and S. L. Smekalov. In the book researches collected information about magnetic prospecting of archaeological sites...
. More than 10 years of using the Overhauser GSM-19 gradiometer", Wormianum 2008.