How do scientists make elements that do not exist in nature?
Oganesson, element 118, was made by firing calcium at californium for four months to produce a first event, and its atoms live for under a thousandth of a second.
▶ Start the storyScientists make these elements by firing one kind of nucleus at another, and then waiting for a rare fusion. Superheavy elements have atomic number at least 104, and they are radioactive and have only been made in laboratories; no macroscopic sample of any of them has ever been produced. In the standard approach a target of heavier nuclei is bombarded with a beam of lighter nuclei.
The problem is that nuclei, all positively charged, repel each other. The strong interaction can overcome this repulsion only within a very short distance, so the beam is greatly accelerated, to speeds as high as one-tenth of the speed of light. Even then, coming close is not enough: nuclei usually stay together about 10^-20 seconds and then part ways. If they do merge, the compound nucleus is excited and very unstable, and it can fission or shed neutrons.
Step 1: Target
Heavier nuclei become the target
Step 2: Beam
Lighter nuclei accelerated up to about 1/10 of light speed
Step 3: Rare fusion
Usually the nuclei just part ways
Step 4: Decay chain
Alpha decays end in a known nucleus
Detection is just as hard. Physicists look for alpha decay chains: if a series of decays produces a known nucleus, the original product can be determined. An element counts as discovered only if its nucleus exists for at least 10^-14 seconds.
The case of oganesson, element 118, shows the scale. Making the first recorded event took four months and 2.5 times 10^19 calcium ions shot at a californium target, and the isotope has a half-life of 0.7 ms, too short for chemical studies.
Quiz me
0/3
Recap
Nuclei repel, so a beam must be fast enough to get close, and fusion is rare enough that discoveries rest on a few decay chains.
💡 A trick to remember it · Throw a bullet at a target until two atom cores glue for a blink, then read the receipts: their decay chain.
Surprising fact · No macroscopic sample of any superheavy element has ever been made.
Sources (4)
No source, no claim. Every fact in this lesson (20 claims) cites at least one of these.