What Is the Island of Stability?
Once in a while one may hear on the news that scientists have created a new element that was never known to exist and fills in a blank spot on the period table. This should excite people because new elements can mean new materials and advancements in science. What shouldn’t excite us is the low life span of these super heavy elements. Why is this the case? As an element gets heavier, it incorporates more protons which have a positive charge and repel each other. The more one has, the greater the repulsion is until the strong nuclear force cannot fight the repulsion and the elements flies apart. But if you incorporate enough neutrons, then isotopes should exist that would withstand these forces and last for years. This is the island of stability that scientists are searching for, and it looks like it should be at 184 neutrons with various proton combinations (Dullmann 49, Francis, Hellmenstine).
This is related to the concept of neutron shells, analogous to electron shells. In the late 1940s, J. Hans D. Jensen developed the idea of neutron shells as a way to strengthen bonding in the nucleus, with closed shells being desired as opposed to open shells that invite decay. Glenn T. Seaborg expanded on this in the late 1960s when he realized that given the right combination of protons and neutrons one could maximize the binding energy that holds our atoms together. But the real inspiration was magic number combinations that scientists found where strong bonding was observed. This included
-152 neutrons with 100 protons
-162 neutrons with 108 protons
-172 neutrons with 120 protons
-184 neutrons with 114 protons
These result in a nucleus with a rigidness that is hard to break, and as one nears the island of stability we encounter more of these magic numbers. And using the total energy included (the mc2 with the binding energy) scientists can estimate what other combinations may work as well (Dullmann 50-1, Francis, Hellmenstine).
On the Hunt
So science says it should be possible, but how would they be created naturally and not in a particle accelerator? Maybe as a result of a supernova or a neutron star collision, both energetic enough to do so. But…no heavy elements like those scientists have been creating have been observed in space yet. In fact nothing has been seen naturally occurring above uranium (92 protons). On Earth, we make superheavies by firing nuclei at speeds greater than 10% c (to overcome electrical repulsion of the nuclei) that creates the energetic conditions required for fusion of a heavy element. But scientists have hit a wall with element 118, because to create it we need nuclei with more than 98 protons and that is unstable as is (Dullmann 51-2).
Do we therefore have enough information to move forward, or at least see what we can expect? Enter element 114 aka Flerovium. Based on its placement on the periodic table, we expect it to be a heavy metal but in 1975 it was demonstrated that Fl114 may be more like a noble gas i.e. inert. The protons in the nucleus may speed up the orbiting electrons to almost 80% c which would goof up the orbital shapes and make them rather difficult to work with chemically. That fits what scientists have seen so far, with no chemical reactions known for the 1-2 second half life element. Element 114 has a slower decay rate that theory predicts and newer elements that have been forged show half-lives (the time it takes for half the element to be remaining) that are longer that predicted as neutron counts increase. That 114 is key, for theory predicts that it should be near our island as long as one can find the right number of neutrons needed as well as the configuration of the nucleus so that the forces are spread out (Dullmann 49-50, 52-3).
Other scientists have done work on mass measurements of superheavy elements near the island such as Nobelium-255 (102 protons and 153 neutrons) and, Lawrencium-255 (103 protons and 152 neutrons), and Lawrencium-256 (103 protons and 153 neutrons). Taking accurate readings is challenging because of the low life span of the elements, so the researchers used a Penning trap to assist them. It involves manipulating electric and magnetic fields to store particles. By measuring the displacements of the particles as they decayed, one could calculate their change in momentum and find the mass from there. By finding the masses of the elements, the binding energy could be calculated and give a clue as to the neutron shell that the superheavy element is experiencing. Other experiments involving synthesizing element 117 had decay products that were Lawreicium-266 (103 protons and 163 neutrons), an even rarer version than the prior ones mentioned. Its half-life was 11 hours, one of the longest seen yet for a superheavy (Francis, Courtland, Moskowitz, Dean, King).
We seem to be getting closer, and when we find that island we will have new material possibilities, special physics, and much much more…
Courtland, Rachel. “Weight scale for atoms could map ‘island of stability.’” Newscientist.com. New Scientist Ltd., 10 Feb. 2010. Web. 19 Sept. 2018.
Dean, Tim. "How to make a superheavy element." cosmosmagazine.com. Cosmos. Web. 12 Mar. 2019.
E. Dullmann, Christopher and Michael Block. “Island of Heavyweights.” Scientific American Mar. 2018. Print. 49-53.
Francis, Matthew. “Shell game: why heavier atoms might get stable again.” Arstechnica.com. Conte Nast., 09 Aug. 2012. Web. 19 Sept. 2018.
Helmenstine, Anne. “Island of Stability – Discovering New Superheavy Elements.” Thoughtco.com. DotDash, 02 Mar. 2018. Web. 19 Sept. 2018.
King, Karen. "Is there an end to the periodic table? MSU professor explores its limits." innovations-report.com. innovations report, 08 Jun. 2018. Web. 12 Mar. 2019.
Moskowitz, Clara. “Superheavy Element 117 Points to Fabled ‘Island of Stability’ on Periodic Table.” Scientificamerican.com. Scientific American, 07 May 2014. Web. 19 Sept. 2018.