Neptunium

Neptunium is an ultra-rare, radioactive, and exceedingly costly element. The substance is seldom found in nature since it exists at such minute levels all around the globe. Due to its employment in neutron detectors, the element is particularly frequent within nuclear plants and labs.

Neptunium is fissionable, and could theoretically be used as fuel in a fast-neutron reactor or a nuclear weapon, with a critical mass of around 60 kilograms. In 1992, the U.S. Department of Energy declassified the statement that neptunium can be used for a nuclear explosive device. It is not believed that an actual weapon has ever been constructed using neptunium. As of 2009, the world production of neptunium by commercial power reactors was over 1000 critical masses a year, but to extract the isotope from irradiated fuel elements would be a major industrial undertaking.

Interestingly, despite being radioactive, some reports suggest scientists haven’t discovered any specific health effects in humans after exposure to neptunium. However, other reports of studies analyzing the impact of neptunium exposure on bones suggest the element can lead to cancer.

Estimated Value: $660 per gram