Neutron Monitor Design Improvements |
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Authors: | Stoker Pieter H Dorman Lev I Clem John M |
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Institution: | (1) Space Research Unit, Potchefstroom University for CHE, Potchefstrom, 2520, South Africa;(2) IZMIRAN, Moscow, Russia;(3) Bartol Research Foundation, Newark, USA |
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Abstract: | The original design by J. A. Simpson of the neutron monitor enabled continuous monitoring of the primary cosmic-ray flux by
ground-based recordings of the nucleonic component with only a rather simple correction for atmospheric effects. Simpson (1957)
extended the original pile to the 12 counter IGY neutron monitor which was deployed in a world wide network during the International
Geophysical Year 1957/8. The desirability for monitors with higher counting rates became evident soon afterwards. Subsequently
the NM64 super neutron monitor was designed by H. Carmichael for deployment in time for the International Quiet Sun Year 1964.
Using unusually large 10BF3 proportional counters made at Chalk River, Hatton and Carmichael (1964) studied comprehensively the experimental design of
the NM64. Consequently the efficiency of neutron counters to record evaporation neutrons produced in the lead of a monitor
increased from 1.9% for the IGY to 5.7% for the NM64, an increase of 3.3 times the counting rate per unit area of lead producer.
During the years much attention was given to the neutron multiplicity spectrum in neutron monitors. This spectrum is related
to the energy spectrum of the nucleonic component incident on the neutron monitor, but is only weakly dependent on the spectrum
of galactic cosmic rays at the top of the atmosphere. Contrary to galactic cosmic rays, solar flare protons and neutrons are
observed predominantly as single counts per interaction, in multiplicity 1, because of the softness of solar flare particle
energy spectra. Neutron monitors have also been specially designed to record solar neutrons with increased sensitivity. Newly
developed 3He counters with a largely reduced thermal neutron absorption mean free path should lead to improved efficiency in recording
primary cosmic radiation. Design criteria are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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