Turning base metals like lead into gold is indeed possible, but you won't get much gold out of it! Have you ever dreamed of becoming rich overnight? What if you could make gold from other metals such as lead? That's exactly what the alchemists of the Middle Ages tried to achieve. Their goal was a "philosopher's stone," an "elixir" or "tincture" that would grant immortality, youth, and deliverance from all diseases, as well as untold riches to those who consumed them. One of the most interesting properties of the elixir was that it could turn any base metal, such as lead, into a sparkling piece of gold. The transformation of one element into another is called transmutation. However, the elixir was legendary, and alchemists never succeeded in turning lead into gold. They were unsuccessful, since no ordinary chemical reaction could turn lead into gold. But could scientists of the modern world, with our expanded chemical knowledge and more advanced instruments, accomplish this chemical feat?
What is the element? Turning lead into gold means turning one element into another. Each element is defined by the number of protons (called atomic number) and neutrons (protons + neutrons = mass number) that make up its nucleus; the number of electrons is not as important to defining an element. Lead has an atomic number of 82 (82 protons in the nucleus) and gold has 79. To turn one element into another, you have to change the number of protons in the nucleus. Changing the number of neutrons (while the number of protons remains the same) in the nucleus results in different kinds of the same element, called isotopes. Lead has four isotopes found in nature and many others created in the laboratory. Turning one element into another These subatomic particles are bound together by strong nuclear forces that keep the nucleus stable. Trying to overcome these forces requires an enormous amount of energy. Removing a proton or neutron from the nucleus would be like trying to lift Thor's hammer, Mjolnir, unless you are pure of heart. Adding a subatomic particle would be like trying to make magnets of the same pole touch. Both adding and subtracting subatomic particles releases an enormous amount of energy. But what if you were able to change the composition of the nucleus? Unfortunately, this gives the element an identity crisis, upsetting the balance of forces within the element. The element begins to emit subatomic particles to reach a more stable state, similar to what happens in radioactive decay. Transmutation by radioactivity Atoms with very large nuclei cannot handle their size, making them unstable. They shed extra weight by ejecting protons and neutrons (alpha radiation), electrons (beta radiation) and electromagnetic radiation (gamma radiation). Most elements after bismuth in the periodic table are radioactive. Radioactive decay is not the best way to produce gold. First, radioactive elements take months or even years or millennia to decay into more common elements. Radium-226 takes 1,600 years to decay by half. Second, radioactive radiation can cause diseases such as cancer and thyroid problems. Thirdly, uranium, thorium, and radium all decay into lead. Lead is stable and does not decay further, which is unfortunate given that gold has only 3 fewer protons than lead.
Nuclear transmutation in a nuclear reactor If we exclude radioactivity, what other method could be used to turn lead into gold? Well, there are several options. Using lead to make gold is not the best strategy because lead has 3 more protons than gold. It is better to use either mercury (1 more proton than gold) or platinum (1 less proton than gold). The earliest experiments to turn a base metal into gold date back to 1924. Independently of each other, researchers Nagoaka in Japan and Miethe and Stammreich in Germany converted mercury to gold by exposing mercury to high electric currents. Later researchers who conducted similar experiments obtained negative results, which called these conclusions into question. Thus, exposing mercury to electric currents may not be the answer. Another option is to bombard mercury or platinum with subatomic particles, such as protons and neutrons. In 1941, researchers bombarded mercury with fast neutrons and turned the metal into gold and platinum. In 1936, researchers bombarded platinum with deuterons (a nucleus with a proton and a neutron; a deuterium nucleus), which produced radioactive isotopes of platinum that decayed into gold. If you have a large stockpile of lead that you need to use, an experiment in 1996 found gold after irradiating lead with 600 MeV protons. How much gold can you make? If you've started dreaming about getting rich making gold, let us break down your dreams. First, most of the gold was radioactive, which means it is likely to decay. Unfortunately, there is no chemical way to turn radioactive gold into regular gold. Second, in all of these experiments, the gold was obtained in amounts of less than 1 mg. Often gold was found only in trace amounts. One report says that the gold obtained by Miethe and Stammreich was only worth $1, but it cost them $60,000 to make! You would be very deep in debt by the time you got any useful gold from such experiments. The researchers who conducted these experiments were more interested in the behavior of atoms and their subatomic particles, not in actually making a fortune in gold. Even if some of these researchers were focused on money, they would rather get rich by discovering something really useful (like an infinite and sustainable energy source). Scientists used their transmutation techniques to create new elements. Elements such as promethium, technetium, and many elements from the lanthanide and actinide series are man-made. In 2020, researchers reported creating a new element with atomic number 113 by fusing zinc atoms with bismuth atoms. One of the researchers working on the project reported that it took more than 4 billion collisions to create the element just three times. Anyway, who cares if you can't make gold out of lead? Scientists are working on even cooler projects - hopefully they will benefit us all!