Atomic particles

The atomic particles which arrive in the vicinity of the Earth range from nuclei of atoms of high atomic weight down to individual nuclear particles such as protons and neutrons. The study of these particles is known as cosmic ray physics. The analysis of the arrival of such particles tells us about some of the energetic processes occurring in the Universe but so far little has come from these observations in us being able to pinpoint the exact sources which generate the energetic particles. Because of the Earth’s magnetic field, any charged particle is deflected greatly from its original direction of travel by the time it arrives at the detector, making it exceedingly difficult to say from which direction in space it originated. At the present time, the Sun is the only body which is definitely known to be a source of particle energy.
It turns out that the basic processes of nuclear (hydrogen) burning within stellar interiors such as the Sun produces the enigmatic neutrino particle. The neutrino has very little interaction with other material and can penetrate great distances through matter. For this reason, the neutrinos generated in the depth of the Sun at a rate ∼10³⁸ s⁻¹ pass from the centre to the surface, escaping very readily outwards. At the distance of the Earth, their flux is ≈10¹⁴ s⁻¹ m⁻², this same number (i.e. ∼10¹⁴) passing through each person’s body per second. Their very low cross section for interaction with other material makes them difficult to detect but some large-scale experiments have been established for this purpose. It must be mentioned that through ‘neutrino’ observatories, astronomy has helped greatly in our understanding of this particle, particularly in relation to the issue of its mass. Although the general flux from other stars is too low for detection, some 10 neutrinos were detected in 1987 from a supernova in the Large Magellanic Cloud. It is estimated that about 10⁹ neutrinos passed through each human being as a result of the event.