#spallation

This Is Why Three Of The Lightest Elements Are So Cosmically Rare

“When you smash a high-energy particle into a massive nucleus, the large nucleus splits apart into a variety of component particles. This process, known as spallation, is how the majority of lithium, beryllium, and boron was formed in our Universe. These are the only elements in the Universe that are primarily formed by this process, rather than by stars, stellar remnants, or the Big Bang itself.

When you look at how abundant all of the elements we know of are, there's a superficially surprising dearth of the 3rd, 4th, and 5th lightest elements of all. There's an enormous gulf between helium and carbon, and at last we know why. The only way to produce these cosmic rarities is by a chance collision of particles streaking across the Universe, and that's why there's only a few billionths the amount of any of these elements compared to carbon, oxygen and helium. Cosmic ray spallation is the only way to make them once we've entered the age of stars, and billions of years later, even these trace elements are essential to the book of life.”

If you were to measure the abundance of each of the elements on the periodic table, you’d find that hydrogen was the most abundant element in the Universe, followed by helium, oxygen, and then carbon. Many other elements show up hot on their heels, including nitrogen, neon, iron, magnesium and silicon. But way, way down, at only around a billionth of these elements, can you find elements like lithium, beryllium and boron. This is surprising, because these are elements number 3, 4 and 5 on the periodic table!

The Scientific Story Of How Each Element Was Made

“Neutron star mergers create the greatest heavy element abundances of all, including gold, mercury, and platinum. Meanwhile, cosmic rays blast nuclei apart, creating the Universe's lithium, beryllium, and boron. Finally, the heaviest, unstable elements are made in terrestrial laboratories. The result is the rich, diverse Universe we inhabit today.”

When the Big Bang first occurred, the Universe was filled with all the various particles and antiparticles making up the Standard Model, and perhaps still others yet to be discovered. But missing from the list were protons, neutrons, or any of the atomic nuclei key to the life-giving elements in our Universe today. Yet the Universe expanded, cooled, antimatter annihilated away, and the first elements began to take shape. After billions of years of cosmic evolution, we arrived at a Universe recognizable today: full of stars, planets, and the full complement of elements populating the periodic table. More than 100 elements are known today, 91 of which are found to occur naturally on Earth. Some were formed in the Big Bang, others were formed in stars, still others were formed in violent cosmic cataclysms or collisions. Yet every one has an origin whose story is now known, giving rise to all we interact with today.

The Rarest Light Elements In The Universe

“[T]he Universe starts off with hydrogen and helium, all stars produce helium, and then stars over a certain mass threshold produce carbon, nitrogen, oxygen and lots of heavier elements. But carbon was already element #6; what about lithium, beryllium and boron (elements #3, #4 and #5)? When we look out at the Universe and the Solar System, and ask what the abundances of the elements are, we notice there's a tremendous gap between helium and carbon, like those three elements are incredibly suppressed.”

Stars fuse hydrogen into helium, then helium into carbon and then it’s up the periodic table to higher and heavier ones via other fusion and neutron-capture mechanisms. But there are three elements in between helium and carbon: lithium, beryllium, and boron. Those three elements can’t be made by conventional fusion, and in fact, aren’t made in stars at all. Although they’re relatively rare in the Solar System and on Earth, they very much exist, and are essential to everything from plants (which need boron for their cell walls) to cellphones (which need lithium for their batteries). Their origin came not from fusion, but through cosmic spallation, where high energy particles blasted apart these heavy nuclei and created these light elements found on our world.

The Only Three Heavy Elements That Aren’t Made In Stars

"[T]he Universe starts off with hydrogen and helium, all stars produce helium, and then stars over a certain mass threshold produce carbon, nitrogen, oxygen and lots of heavier elements. But carbon was already element #6; what about lithium, beryllium and boron (elements #3, #4 and #5)?"