Cosmic ray spallation in the context of "Oddo–Harkins rule"

Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the nucleus of an in situ Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom (see cosmic ray spallation). These nuclides are produced within Earth materials such as rocks or soil, in Earth's atmosphere, and in extraterrestrial items such as meteoroids. By measuring cosmogenic nuclides, scientists are able to gain insight into a range of geological and astronomical processes. There are both radioactive and stable cosmogenic nuclides. Some of these radionuclides are tritium, carbon-14 and phosphorus-32.

Certain light (low atomic number) primordial nuclides (isotopes of lithium, beryllium and boron) are thought to have been created not only during the Big Bang, but also (and perhaps primarily) to have been made after the Big Bang, but before the condensation of the Solar System, by the process of cosmic ray spallation on interstellar gas and dust. This explains their higher abundance in cosmic dust as compared with their abundances on Earth. This also explains the overabundance of the early transition metals just before iron in the periodic table – the cosmic-ray spallation of iron produces scandium through chromium on the one hand and helium through boron on the other. However, the arbitrary defining qualification for cosmogenic nuclides of being formed "in situ in the Solar System" (meaning inside an already aggregated piece of the Solar System) prevents primordial nuclides formed by cosmic ray spallation before the formation of the Solar System from being termed "cosmogenic nuclides"—even though the mechanism for their formation is exactly the same. These same nuclides still arrive on Earth in small amounts in cosmic rays, and are formed in meteoroids, in the atmosphere, on Earth, "cosmogenically". However, beryllium (all of it stable beryllium-9) is present primordially in the Solar System in much larger amounts, having existed prior to the condensation of the Solar System, and thus present in the materials from which the Solar System formed.

Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three valence electrons for forming covalent bonds, resulting in many compounds such as boric acid, the mineral sodium borate, and the ultra-hard crystals of boron carbide and boron nitride.

Boron is synthesized entirely by cosmic ray spallation and supernovas and not by stellar nucleosynthesis, so it is a low-abundance element in the Solar System and in the Earth's crust. It constitutes about 0.001 percent by weight of Earth's crust. It is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. The largest known deposits are in Turkey, the largest producer of boron minerals.

Sulfur (₁₆S) has 23 known isotopes with mass numbers ranging from 27 to 49, four of which are stable: S (94.85%), S (0.76%), S (4.37%), and S (0.016%). The preponderance of sulfur-32 is explained by its production from carbon-12 plus successive fusion capture of five helium-4 nuclei in the alpha process of nucleosynthesis.

The main radioisotope S is formed from cosmic ray spallation of Ar in the atmosphere. Other radioactive isotopes of sulfur are all comparatively short-lived. The next longest-lived radioisotope is sulfur-38, with a half-life of 170 minutes. Isotopes lighter than S mostly decay to isotopes of phosphorus or silicon, while S and heavier radioisotopes decay to isotopes of chlorine.

In geochemistry, geophysics and nuclear physics, primordial nuclides, or primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the Solar System was formed, and were formed in the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, or from other processes throughout the history of the universe. They are the stable nuclides plus the fraction of the long-lived radionuclides surviving from the primordial solar nebula through planet accretion until the present; 286 such nuclides are known.