Answer to Question #4086 Submitted to "Ask the Experts"

How are synthetic elements made?

There are a few ways in which synthetic elements can be made. Keep in mind that the identity of an element is defined by the number of protons in the nucleus of each atom of the element. Thus, in order to manufacture a new element, one that is not known in nature, we must create at least one atom whose atomic number (the number of protons in the nucleus) is different from any other known element. In reality, we typically require a rather large number of atoms in order to be able to characterize them as representing a new element. One possible way to accomplish this involves irradiating existing elements with selected nuclear particles, including such particles as neutrons, protons, helium nuclei, and nuclei of heavier atoms, in such a fashion that some of these particles may get incorporated into the nuclear structure of the atoms of the elements being irradiated. The new nucleus that results may be different from any nucleus that exists naturally and/or it may be radioactive and decay to some other nuclear arrangement that may constitute a new nucleus.

For example, californium, with atomic number of 98, is a man-made element that was originally made in 1950 by bombarding an element called curium, a previously discovered synthetic element, with high-energy helium ions produced in a machine called a cyclotron, which is a type of charged-particle accelerator that can cause charged particles to develop high kinetic energies; these high-energy particles can then be used to bombard the nuclei of target atoms with the possibility of changing the nuclear configuration. Thus, curium, with 96 protons in its nucleus, can be bombarded by high-energy helium ions, each containing two protons along with two neutrons, to yield californium with 98 protons in its nucleus. Californium, symbolized Cf, particularly an isotope (isotopes of an element are species with the same numbers of protons in their nuclei but with different numbers of neutrons) referred to as californium-252 (252 is the combined number of neutrons plus protons in the nucleus), can also be made by bombarding selected target nuclei in an intense field of neutron radiation, most often in a nuclear reactor; such reactors are our most prolific sources of neutrons. Californium-252 has the property that it undergoes a spontaneous fission process to such an extent that it is an intense source of neutrons that have had a variety of applications in medicine, industry, and in research. Beginning with an isotope of plutonium, plutonium-239, it is possible to make several different isotopes of californium through a series of neutron capture and radioactive decay events.

There are a number of other heavy elements (heavier than uranium) that have been produced using accelerators and/or reactors. In nuclear reactors, the intense neutron fields are generated when uranium atoms split (called fission) into two lighter fragments, in the process emitting a few neutrons each time a uranium atom fissions. As it turns out, the fission process itself may lead to new elements. In fact, probably the most commonly used radioactive species in nuclear medicine (nuclear medicine is a field of medicine in which radioactive materials are administered to patients in order to diagnose various ailments) is an isotope of technetium (referred to as technetium-99m). The technetium-99m comes about from the radioactive decay of an isotope of molybdenum, molybdenum-99, that is sometimes produced as a fission fragment when uranium fissions. There are a total of 22 known isotopes of technetium, and all are man-made, not all in reactors, however. Work is continuously ongoing to synthesize new elements with a lot of interest in very heavy elements with atomic numbers around 114 and higher.

If you would like to learn more about the discovery of the elements, including man-made elements, you can find considerable information on the Internet. I particularly enjoy a site sponsored by the Radiochemistry Society. Click on the Periodic Table and when the table comes up click on any element to learn something about its discovery and its properties. Pay particular attention to the elements at the bottom of the periodic table, referred to as the Actinide Series, since these contain many, but not all, of the man-made transuranic elements (elements beyond uranium in the table). Good luck.

George Chabot, PhD, CHP