Difference of Neutron counts versus Muon counts!

These 2 very nice online neutron detectors cosmicrays.oulu.fi and helios.izmiran.rssi.ru/cosray/main.htm clearly show a diurnal variation and sometimes quite intense forbush decreases in neutron radiation.

On the other hand this online muon detector www2.slac.stanford.edu/vvc/cosmicrays/crdatacenter.html doesn't show that quite strong variations.

The explanation of the difference is quite simple, if you consider how the secondary particles like neutrons and muons are produced in our atmosphere.

Neutrons can be produced at relatively low primary energies. A primary with an energy of bigger than ~500MeV causes nuclear interactions and can knock neutrons out of a nucleus. Such a primary is however not so likely to result in a muon. Most of the neutrons detected by the neutron detectors are produced by primaries in the 1 to 20 GeV range.

The muons detected at sea level, however, have an energy distribution that peaks at around 3 GeV (and that is at sea level, so at the top of the atmosphere the muons have about 5 GeV). They come from pions produced in air showers. The energies of the primaries are much higher than the 1-20 GeV range, and the higher the energy, the more pions are produced which then decay into muons.

The day-night effect depends heavily on the energy of the primary.
The neutrons come from much lower energy primaries than the muons, and the effects of relatively local fluctuations in Earth's magnetic field on low energy primaries are therefore much bigger.

In general we can say that the majority of neutrons is produced by lower energy primary particles. Therefore the neutron monitors do detect rather strong diurnal variation and Forbush decreases, since Earth's magnetic field has stronger influence on lower energy primaries.
Only higher energy primary particles are capable of producing pions (->muons) and these primaries are much less affected by Earth's magnetic field. The Sun seldomly produces particles with a high enough energy to produce muons in our atmosphere, so most muon-producing primary particles are GCR's (galactic cosmic rays from i.e. Supernovae).

Particle decay!

• Cosmic rays hit Earth's atmosphere and produce pions.
• Charged Pions decay into muons and muon neutrinos, and neutral pions decay into photons. Muons, produced by the charged Pions are then also charged.
• Muons decay into an electron or positron (the antiparticle of the electron), a neutrino and a antineutrino.
• A neutral pion, as mentioned above, decays into two photons.

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