Particle Intensity - Muons and Neutrinos - Cosmic Radiation Flux

100 to 200 muons per square meter per second (at sea level)
That makes about 1-2 particles per square decimeter per second
or if we use our hand for comparison: 1-2 muons per second pass thru your open hand

~6·10¹⁴ solar neutrinos per square meter per second (solar neutrino flux)
600000 billions neutrinos per square meter per second
6000 billions neutrinos per square decimeter per second
60 billion neutrinos per square centimeter per second
or if we use our hand for comparison: 6000 billions neutrinos pass thru your open hand per second
or if we use one thumbnail for comparison: 60 billion neutrinos pass thru your thumbnail per second
Also see: Solar Neutrinos - Calculation of the solar neutrino flux on Earth

Galactic cosmic rays (GCR) vs. solar cosmic rays (SCR)!

Sun continually expels countless particles due flares and eruptions, so why don't these produce large amounts of Muons when those particles hit Earth's atmosphere ?

The answer is simple. Particles from the Sun usually aren't accelerated enough to have a high enough energy to produce secondary particles in our atmosphere. Particles in the solar wind (95% protons and electrons (in roughly equal numbers); 4% alpha particles (He²⁴); the remaining 1% are isotopes such as helium-3, helium-4, neon-20, neon-21, neon-22, and argon-36) usually have energies from 1 - 10⁴eV. But sometimes, mostly during strong flares, particles from Sun can be accelerated to nearly the speed of light, having more than 300 MeV, so they produce pions (which decay into muons) in Earth's atmosphere. But this is the exception and happens very seldom. The muons we detect are almost 100% from GCR's.

Note on SCR composition:
Oxygen (mass 16) is actually the most abundant heavy element in the solar wind, and the true Iron (mass 56) abundance would be roughly 10% that of Oxygen.

Note on GCR composition:
Cosmic rays include essentially all of the elements in the periodic table; about 89% of the nuclei are hydrogen (protons), 10% helium, and about 1% heavier elements. The common heavier elements (such as carbon, oxygen, magnesium, silicon, and iron) are present in about the same relative abundances as in the solar system, but there are important differences in elemental and isotopic composition that provide information on the origin and history of galactic cosmic rays. For example there is a significant overabundance of the rare elements Li, Be, and B produced when heavier cosmic rays such as carbon, nitrogen, and oxygen fragment into lighter nuclei during collisions with the interstellar gas. The isotope ²²Ne is also overabundant, showing that the nucleosynthesis of cosmic rays and solar system material have differed. Electrons constitute about 1% of galactic cosmic rays. It is not known why electrons are apparently less efficiently accelerated than nuclei. (by R. A. Mewaldt)

Magnetic Fields!

Charged particles such as cosmic rays are deflected by magnetic fields. There is the galactic magnetic field, interstellar magnetic fields, the solar magnetic field and of course Earth's magnetic field. Therefore it is impossible to determine the origin of galactic cosmic rays via the incoming direction. GCR's are first deflected by the galactic MF and interstellar MF's, when they enter our solar system they are deflected by the solar MF and if they come near Earth they are even more deflected by Earth's MF. These MF's are not constant, but vary with time, especially the latter two. Furthermore there are local variations of the MF in the solar system (long term: solar cycle; short term: magnetic clouds produced by solar flares) and of Earth's MF caused by variations of the solar wind.

Long term variation: Cosmic particles increase and decrease with the solar cycle!

On average, every eleven years solar activity is high. The magnetic field of the sun increases, solar flares are more common, which produce magnetic clouds and therefore cosmic rays are deflected stronger than during a solar minimum. Thus, when the sun is active, fewer galactic cosmic rays reach Earth's atmosphere in order to produce secondary particles.

Short term variation: diurnal and semidiurnal

Daily variations in counting rates of ground based cosmic ray detectors show the intensity of galactic cosmic rays (GCR) in space. These variations have diurnal (a pure sine wave with a period of 24 hours) and semidiurnal components.

Short term variation: Forbush decrease!

Forbush decreases occurs when the sun releases an exceptionally large burst of matter and magnetic disturbance (magnetic cloud). The disturbance sweeps away some of the cosmic rays in its path and prevents many cosmic rays from entering the atmosphere. When the disturbance (magnetic cloud) passes earth a Forbush decrease is seen on the particle detector.

These disturbances typically travel at a speed of 400-1000 km/s, and take 2-4 days to travel from the sun to the earth. Cosmic ray intensity dips within a few hours, and then slowly recovers over the next few days.

Earth directed coronal mass ejections (CME's) and shock waves are detectable earlier with ground-level cosmic ray muon telescopes than with neutron monitors.

Also see: Xray burst - Radio Burst - Coronal Mass Ejection (CME) Cosmic Ray Forbush Decrease - Magnetic Field Distortion

Particle air showers!

The atmosphere serves as a natural transducer and amplifier for the detector. The primary cosmic rays collides with nucleii in the air, creating many secondary particles which share the original energy. The secondary particles also collide with nuclei in the air, creating a new generation of still more particles that continue the process. This cascade, sometimes called an "extensive air shower," arrives at ground level with billions of energetic particles that can be detected over about 10km².

Cosmic Rays and the Weather on Earth!

Low-energy cosmic rays like the solar wind cause ionization in the upper atmosphere. Muons are responsible for most of the ionization in the lower atmosphere. When a muon ionizes a gas molecule, it strips away an electron, making that molecule into a positive ion. The electron is soon captured, either by another gas molecule turning it into a negative ion, or it may find an already ionized positive ion and neutralize it (this is called recombination). The ionization and recombination effect is balanced, so the density of positive and negative ions in the atmosphere is fairly constant. But the negative ions are more "mobile" than the positive ions, so this results in an electric field, which is about 100 V/m on a quiet day.

The formation of a thunderstorm is still under investigation, but as far as we know the negative ions are lifted up and the positive ions are pushed down, forming an electric field of 1000s of V/m. If the field is high enough, discharge (lightning) occurs. Without ionization, thunder and lightning would not happen, so cosmic rays have a direct influence on Earth's weather.

Scientists are also investigating influence of cosmic rays on cloud formation. There is evidence for correlation between cosmic ray flux and low-altitude cloud formation, but correlation does not always imply causation. One possible mechanism for this could be: elevated levels of ionization seem to facilitate the coagulation of such molecules as sulfuric acid (H2SO4) in the atmosphere into tiny droplets, which then form condensation nuclei for water vapor. The condensed droplets of water then form clouds.

Dr. Nir Shaviv presented a paper about this matter ("On the link between cosmic rays and the terrestrial climate") at the ECRS 2004 in Florence/Italy. The slides of the presentation are available at the ECRS2004 homepage.

Neutrino-induced Muons - NIM's

Neutrino's interact with matter very rarely, therefore the detection is very difficult. Most Neutrino detectors are Cherenkov-light based liquid (i.e. heavy water) detectors.
In seldom cases, when the energy of one neutrino is high enough it may interact with matter and produce a muon. Since there are plenty of muon's from above (regular secondary particles and air showers) it is impossible to detect neutrino-induced muon's from above, but it is possible to detect those secondaries from below, because atmospheric muons don't come from below. Neutrinos flying thru Earth may interact with matter (i.e. solid rock) nearby, but outside the detector and produce muons from below, which are easy to detect with a directional detector.

Proposal: abbreviation for "Neutrino-induced Muon": NIM

Actually this sort of interaction is very rare, so let's see if that sort of muon's can be detected with amateur equipment.
UPDATE: There might be regular low-energy muons from below, which actually came from above, but due their low energy they are bounced back by matter and fly thru the detector from below. It is uncertain, if that low energy required to reverse their direction is still high enough to penetrate both detectors and generate events in both detectors.

Cherenkov radiation (Cherenkov light)

If the particle's speed is higher than the speed of light in the medium, electro-magnetic (Cherenkov) radiation is emitted.

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