Cosmogenic nuclide

Cosmogenic nuclides (or cosmogenic isotopes) are rare <a href="/facts/Nuclide/97Ykvzr3">nuclides</a> (<a href="/facts/Isotope/KD9B1y6o">isotopes</a>) created when a high-energy <a href="/facts/Cosmic_ray/uxCVdTKd">cosmic ray</a> interacts with the <a href="/facts/Atomic_nucleus/orpIm5Xl">nucleus</a> of an <a href="/facts/In_situ/YolKlaCC">in situ</a> Solar System <a href="/facts/Atom/FoQ4kGN5">atom</a>, causing nucleons (protons and neutrons) to be expelled from the atom (see <a href="/facts/Cosmic_ray_spallation/gSlq9VEP">cosmic ray spallation</a>). These nuclides are produced within Earth materials such as <a href="/facts/Rock_(geology)/FXCJkmop">rocks</a> or <a href="/facts/Soil/5Ddpr3QM">soil</a>, in <a href="/facts/Earth/HLLmDfj0">Earth's</a> <a href="/facts/Earth%27s_atmosphere/FV97Am25">atmosphere</a>, and in extraterrestrial items such as <a href="/facts/Meteoroid/5PexF2mR">meteoroids</a>. By measuring cosmogenic nuclides, <a href="/facts/Scientist/JDvthEFM">scientists</a> are able to gain insight into a range of <a href="/facts/Geology/WGvVRIYF">geological</a> and <a href="/facts/Astronomy/0ArJVM1p">astronomical</a> processes. There are both <a href="/facts/Radioactive_isotope/5WpCfbdq">radioactive</a> and <a href="/facts/Stable_isotope/vgcdxgjA">stable</a> cosmogenic nuclides. Some of these radionuclides are <a href="/facts/Tritium/HWSa6EHy">tritium</a>, <a href="/facts/Carbon-14/Ut8SBNNa">carbon-14</a> and <a href="/facts/Phosphorus-32/aEWwgebr">phosphorus-32</a>.
Certain light (low atomic number) <a href="/facts/Primordial_nuclides/lFAUqHDv">primordial nuclides</a> (isotopes of <a href="/facts/Lithium/7vXX6BWA">lithium</a>, <a href="/facts/Beryllium/dv295voP">beryllium</a> and <a href="/facts/Boron/Pmwgd7Mf">boron</a>) are thought to have been created not only during the <a href="/facts/Big_Bang/I5T1vTnv">Big Bang</a>, 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 <a href="/facts/Transition_metal/0slGWoLQ">transition metals</a> just before <a href="/facts/Iron/QK1JYy8E">iron</a> in the periodic table – the cosmic-ray spallation of iron produces <a href="/facts/Scandium/TJRt1chg">scandium</a> through <a href="/facts/Chromium/6sVk6Uu7">chromium</a> on the one hand and <a href="/facts/Helium/yRul93TG">helium</a> 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 (<a href="/facts/Mononuclidic_element/3hmC7IpX">all of it</a> 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.
To make the distinction in another fashion, the timing of their formation determines which subset of cosmic ray spallation-produced nuclides are termed primordial or cosmogenic (a nuclide cannot belong to both classes). By convention, certain stable nuclides of lithium, beryllium, and boron are thought to have been produced by cosmic ray spallation in the period of time between the <a href="/facts/Big_Bang/I5T1vTnv">Big Bang</a> and the Solar System's formation (thus making these <a href="/facts/Primordial_nuclide/lFAUqHDv">primordial nuclides</a>, by definition) are not termed "cosmogenic", even though they were formed by the same process as the cosmogenic nuclides (although at an earlier time). The primordial nuclide beryllium-9, the only stable beryllium isotope, is an example of this type of nuclide.
In contrast, even though the radioactive isotopes <a href="/facts/Beryllium-7/bNvHB5xg">beryllium-7</a> and <a href="/facts/Beryllium-10/oz3rQBLB">beryllium-10</a> fall into this series of three light elements (lithium, beryllium, boron) formed mostly by cosmic ray spallation <a href="/facts/Nucleosynthesis/F9MIeADF">nucleosynthesis</a>, both of these nuclides have half lives too short (53 days and ca. 1.4 million years, resp.) for them to have been formed before the formation of the Solar System, and thus they cannot be primordial nuclides. Since the cosmic ray spallation route is the only possible source of beryllium-7 and beryllium-10 occurrence naturally in the environment, they are therefore cosmogenic.

Cosmogenic nuclide open-in-new

Cosmogenic nuclide