From:
http://chemistry.about.com/cs/generalchemi...a/aa050601a.htm


Before Chemistry was a science, there was Alchemy. One of the supreme quests of alchemy is to transmute lead into gold. Lead (atomic number 82) and gold (atomic number 79) are defined as elements by the number of protons they possess. Changing the element requires changing the atomic (proton) number. The number of protons cannot be altered by any chemical means. However, physics may be used to add or remove protons and thereby change one element into another. Because lead is stable, forcing it to release three protons requires a vast input of energy, such that the cost of transmuting it greatly surpasses the value of the resulting gold.

Transmutation of lead into gold isn't just theoretically possible - it has been achieved! There are reports that Glenn Seaborg, 1951 Nobel Laureate in Chemistry, succeeded in transmuting a minute quantity of lead (possibly en route from bismuth, in 1980) into gold. There is an earlier report (1972) in which Soviet physicists at a nuclear research facility near Lake Baikal in Siberia accidentally discovered a reaction for turning lead into gold when they found the lead shielding of an experimental reactor had changed to gold.

Today particle accelerators routinely transmute elements. A charged particle is accelerated using electrical and/or magnetic fields. In a linear accelerator, the charged particles drift through a series of charged tubes separated by gaps. Every time the particle emerges between gaps, it is accelerated by the potential difference between adjacent segments. In a circular accelerator, magnetic fields accelerate particles moving in circular paths. In either case, the accelerated particle impacts a target material, potentially knocking free protons or neutrons and making a new element or isotope. Nuclear reactors also may used for creating elements, although the conditions are less controlled.

In nature, new elements are created by adding protons and neutrons to hydrogen atoms within the nuclear reactor of a star, producing increasingly heavier elements, up to iron (atomic number 26). This process is called nucleosynthesis. Elements heavier than iron are formed in the stellar explosion of a supernova. In a supernova gold may be made into lead, but not the other way around.