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NEUTRON MONITORS

 Neutron monitors are ground-based recorders of cosmic rays. Cosmic rays are highly energetic charged particles (predominantly protons, together with heavier nuclei of atoms, but also electrons and gamma rays) originating in the galaxy and traveling through interstellar space. They have to propagate through the interplanetary magnetic field that is frozen into the solar wind, and the Earth’s magnetic field before they arrive at the Earth’s atmosphere. Due to collisions with nuclei of atmospheric atoms, showers of secondary particles are produced. The nuclear active components of the secondaries are detected by a neutron monitor.

 The counting rate of a neutron monitor is, therefore, a measure of the intensity of cosmic rays arriving at Earth. Since cosmic rays do not arrive isotropically (with the same intensity in all directions), an optimal distribution of neutron monitors across the Earth’s surface is required to derive the time-dependent directionality and intensity spectrum of cosmic rays within the energy range of detection on Earth.

 Very few of the approximately 40 well-operating neutron monitors are in the Southern Hemisphere. Of these, the Tsumeb, Potchefstroom, Hermanus and SANAE neutron monitors provide a unique latitudinal chain of recorders from near the equator to Antarctica. The operation of these neutron monitors and their data processing, for international use, are part of the research program of the Unit for Space Physics at the Potchefstroom Campus of the North-West University. 

 The four neutron monitors are:

   

		Tsumeb – Namibia (190 12’ S, 170 35’ E, altitude 1240 m.a.s.l., ambient atmospheric pressure 660 mm Hg) The 18NM64 neutron monitor operates at a research station that was established by the Max Planck Institue for Aeronomy in 1957 for ionospheric observations during the IGY. Presently, the station is maintained by the Geological Survey of Namibia. The station is situated about 12 kilometers north-west from the town of Tsumeb, in the northern part of Namibia. The photograph of the buildings was taken from one of the high towers of the ionosonde antenna on the site.
		Potchefstroom  - South Africa (260 41.9’ S, 270 05.6’ E, altitude 1351 m.a.s.l., ambient atmospheric pressure 652 mm Hg) The 15 counter IGY-type neutron monitor is situated on the roof of the Physics building of the Potchefstroom Campus of the North-West University. This building houses the Research Unit for Space Physics, responsible for the processing of the data recorded by this chain of neutron monitors.
		Hermanus – South Africa (340:25.5’ S, 190:13.5’ E, altitude 26 m.a.s.l., ambient atmospheric pressure 760 mm Hg) Hermanus is a town at sea level close to the southern point of Africa. It is a picturesque seaside resort, famous for whale watching. The neutron monitor is operated by the Hermanus Magnetic Observatory since the International Geophysical Year (IGY), from July, 1957. Currently it consists of 12 NM64 Chalk River neutron counter tubes, and it is the second oldest continuously operating neutron monitor.
		Note:  From 7 August 1994 through to 31 December 2002 there was a drift in the pressure transducer "20" such that the values of pressure 20 of the small time data have to be increased by 0.000627 mm Hg (or 0.00627 in 0.1 mm Hg) per day. These corrections have been done for all the hourly data files, except the  tabulated values of corrected and pressure data.
		SANAE IV – Antarctica, since April 1997 on Vesleskarvet, a small outcrop (nunatak). (710 40’ S, 020 51’ W, altitude 856 m.a.s.l., ambient atmospheric pressure 660 mm Hg). SANAE IV is 170 km inland from the former South African bases, SANAE I, II, and III, which were on the ice shelf at 52 m.a.s.l., ambient atmospheric pressure 987.2 mb. On the previous bases, the 3NM64 neutron monitor was placed on scaffolding that could be elevated to keep it clear from the rising snow level. When the monitor was shifted to Vesleskarvet in 1997, it was increased to a 6NM64, and it is situated on the upper floor of the station building, which is situated on rock and does not suffer from a changing snow environment.

 History of NEUTRON MONITORS of the UNIT of SPACE PHYSICS, SCHOOL of PHYSICS, NORTH-WEST UNIVERSITY,  POTCHEFSTROOM Campus, SOUTH AFRICA

In the list below is given the name (location) of the station, followed in brackets by the geographic latitude and longitude, the altitude in meters above sea level (m.a.s.l.), the average pressure for pressure corrected count rates, and the vertical cutoff rigidity in GV for the epochs 1980.0 and/or 1990.0*. The type of neutron monitor and the period of operation is given subsequently, followed by the counts per hour equivalent to May, 1965.

At Tsumeb (19⁰ 12’ S, 17⁰ 35’ E, 1240 m.a.s.l., 660 mm Hg, 9.15 GV, 9.12* GV), since December 1976: 18NM64, 1,204,000 counts/hr.

At Potchefstroom (26⁰ 41.9’ S, 27⁰ 05.6’ E, 1351 m.a.s.l., 652.4 mm Hg, 6.94 GV, 6.98* GV), since May 1971: 12IGY, 211,600 counts/hr

At Hermanus (34⁰ 25.5’ S, 19⁰ 13.5’ E, 26 m.a.s.l., 760 mm Hg, 4.58 GV, 4.44* GV), from July 1957 through to June 1964: 12IGY, 16x3620 bihourly counts/hr, from August 1964 through to July 1972: 3NM64, 105,620 counts/hr, from August through to December 1972: 9NM64, 357,100 counts/hr, since January 1973: 12NM64, 455,830 counts/hr.

At Sanae-1, -2 and -3 (70⁰ 19’ S, 02⁰ 21’ W, 52 m.a.s.l., 987.2 mb, 0.86 GV), from February 1964 through to December 1994: 3NM64, 151,600 counts/hr, from April 1974 through to December 1994: 4NMD, 14,450 counts/hr.

At Sanae-4 on Vesleskarvet (71⁰ 40’ S, 02⁰ 51’ W, 856 m.a.s.l., 660 mm Hg, 0.73* GV), since April 1997: 2 x 3NM64, 643,500 counts/hr, and 4NMD, 32,600 counts/hr.

Pressure drift

Hermanus 12NM64 tabulated pressure and pressure corrected hourly values from 7 August 1994 to 31 December 2002.

Because of a small drift in the second pressure, the values of Pressure have to be increased by 0.000627 mm Hg (or 0.00627 in 0.1 mm Hg) per day since 7 August 1994 through to 31 December 2002.

Small time data

Hermanus: From 1985 to 1996

Small time data for other periods of our stations are available on request from Pieter H Stoker at fskphs@puk.ac.za

 

 

Tsumeb, Potchefstroom, Hermanus and SANAE data         1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

 

Ground level events (GLE) of the Potchefstroom chain of Neutron Monitors are available at the international data centre of GLE's or on request from Pieter H Stoker at fskphs@puk.ac.za

 

Ground Level Events (GLE) #55_971106 #56_980502 #57_980506 #58_980824 #59_000714 #60_010415 #61_010418 #62_011104 #63_011226 #64_020824 #65_031028 #66_031029 #67_031102 #69_050120

 

Monthly Neutorn Monitor variation

 

UNIT OF SPACE PHYSICS
School of Physics
North-West University
Potchefstroom Campus
Private Bag X6001
Potchefstroom
2520
Republic of South Africa
Tel:  +27 18-299-2422
Fax: +27 18-299-2421
E-Mail: fskphs@puk.ac.za  [Pieter H Stoker]