The identity of any element is defined by the number of protons contained within its atomic nucleus, a count known as the atomic number. This rule dictates the entire periodic table. The process of generating new elements, called nucleosynthesis, has taken place across a vast cosmic timeline, beginning in the universe’s first moments and continuing today in specialized laboratories. These creation events occur in fundamentally different environments, each providing the specific energy and particle flux required to fuse smaller nuclei into larger ones.
Creation of the Universe’s Lightest Elements
The very first elements were forged during Primordial Nucleosynthesis, a brief, high-energy period that began just seconds after the Big Bang. As the universe expanded and cooled, protons and neutrons began to combine into atomic nuclei. Deuterium, a form of hydrogen with one proton and one neutron, was the first stable product formed. This deuterium quickly fused into helium-4 nuclei, accounting for roughly 25% of the baryonic mass of the early universe. Trace amounts of lithium (element number three) were also created during this short window of time. The process halted abruptly because the universe cooled too rapidly for the formation of elements heavier than lithium to be sustained. Furthermore, the lack of stable nuclei with five or eight protons and neutrons created gaps in the fusion chain, preventing the creation of carbon and heavier elements.
Element Formation Inside Stars
Stars serve as the universe’s natural, long-lived fusion reactors, taking the hydrogen and helium left over from the Big Bang and building heavier elements. In stars like our sun, the primary method for hydrogen fusion is the proton-proton chain, where four hydrogen nuclei are converted into a single helium nucleus. In more massive and hotter stars, the Carbon-Nitrogen-Oxygen (CNO) cycle dominates, using those elements as catalysts to achieve the same result.
As stars age and exhaust core hydrogen, they begin to fuse helium into carbon and oxygen through the triple-alpha process, which requires much higher temperatures. Subsequent burning stages in massive stars allow for the creation of progressively heavier elements:
- Neon
- Magnesium
- Silicon
- Sulfur
This stellar fusion continues until the core is predominantly iron (Fe). Iron nuclei possess the highest binding energy per nucleon, meaning that fusing iron requires an input of energy rather than releasing it, making further fusion energetically unfavorable.
Forging Elements Heavier Than Iron
The creation of elements heavier than iron necessitates the extreme conditions of explosive cosmic events. These elements are primarily forged through the capture of free neutrons, a mechanism that bypasses the energy barrier of fusion. The slow neutron-capture process, or s-process, occurs in aging, low- to intermediate-mass stars. Here, neutrons are captured slowly, allowing for radioactive decay between additions to form elements like barium and strontium.
The heaviest elements, including gold, platinum, and uranium, are overwhelmingly created by the r-process, or rapid neutron-capture process. This requires an environment with an immense density of free neutrons, such as a supernova explosion or the merger of two neutron stars. In these catastrophic events, atomic nuclei are bombarded by a flood of neutrons, absorbing many before they decay. They subsequently transform into stable heavy elements after the event subsides. Recent observations confirm that neutron star mergers are a major site for the production of these heaviest naturally occurring elements.
Synthesizing New Elements on Earth
Elements with an atomic number of 93 or higher do not exist naturally on Earth in significant amounts and must be created in laboratories. This is accomplished using powerful particle accelerators to initiate nuclear fusion-evaporation reactions. The process involves firing a beam of high-speed ions, such as calcium-48, at a target made of a heavy element like curium or californium.
When the projectile and target nuclei collide, they momentarily fuse into a single, highly unstable compound nucleus. This excited nucleus quickly sheds its excess energy by “evaporating” a few neutrons before settling into a new, heavier element. These newly synthesized transuranic and superheavy elements are extremely fragile and often exist for only a fraction of a second. For instance, some isotopes decay in as little as a fifth of a second, while others last only a few milliseconds. This fleeting existence makes their detection and study a significant challenge for modern nuclear physics.