Neutron monitor

<p>A neutron monitor is a ground-based <a href="/facts/Particle_detector/rYj0qKtA">detector</a> designed to measure the number of high-energy charged <a href="/facts/Subatomic_particle/tMEzcTWQ">particles</a> striking the <a href="/facts/Earth%2527s_atmosphere/FV97Am25">Earth's atmosphere</a> from <a href="/facts/Outer_space/R3LRKyFs">outer space</a>. For historical reasons the incoming particles are called "<a href="/facts/Cosmic_ray/uxCVdTKd">cosmic rays</a>", but in fact they are particles, predominantly <a href="/facts/Protons/clCjepXP">protons</a> and <a href="/facts/Helium/yRul93TG">Helium</a> <a href="/facts/Nucleus_(atomic_structure)/orpIm5Xl">nuclei</a>. Most of the time, a neutron monitor records <a href="/facts/Galactic_cosmic_ray/uxCVdTKd">galactic cosmic rays</a> and their variation with the 11-year <a href="/facts/Sunspot_cycle/QrP4Egea">sunspot cycle</a> and 22-year <a href="/facts/Hale_cycle/QrP4Egea">magnetic cycle</a>. Occasionally the <a href="/facts/Sun/CadPCVHh">Sun</a> emits cosmic rays of sufficient energy and intensity to raise radiation levels on Earth's surface to the degree that they are readily detected by neutron monitors. They are termed "<a href="/facts/Ground_level_enhancement/ogLdIc5E">ground level enhancements</a>" (GLE).
</p><p>The neutron monitor was invented by <a href="/facts/University_of_Chicago/z6zRMUmV">University of Chicago</a> Professor <a href="/facts/John_Alexander_Simpson/8HsIplFz">John A. Simpson</a> in 1948. The "18-tube" NM64 monitor, which today is the international standard, is a large instrument weighing about 36 tons.
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Neutron monitor open-in-new

Neutron monitor