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IYPT Elements

IYPT 2019 Elements 093: Neptunium: Radioactivity and smoke detector byproduct

Element 93 in our International Year of the Periodic Table series is neptunium. Neptunium is a radioactive metal with few uses – though it is found in smoke detectors, and is also predicted to have the largest liquid range of any element.

Neptunium is sandwiched between two better known radioactive elements: uranium and plutonium. It is itself radioactive and is largely generated by the irradiation of uranium in nuclear reactors. It’s estimated that around 2500 kilograms of neptunium was released into the atmosphere as a result of nuclear testing prior to the partial nuclear test ban treaty in 1963.

Neptunium itself has few current uses. Though, like uranium, it is fissionable, it has never been used as the basis for a nuclear reactor or weapon. It does appear in small (and safe) amounts in our homes, due to the radioactive decay of the americium used in smoke detectors.

One distinction that neptunium can lay claim to is that it’s possibly the element that’s liquid over the largest range of temperatures. It melts at around 640 ˚C; while its boiling point has never been directly measured, it’s calculated to be 4174 ˚C. If this is indeed the case, it has a larger liquid range than gallium, which lays claim to the title if only directly measured temperatures for melting and boiling point are used.

Remember, you can keep track of all of the previous entries in this series on the site here, or on the Royal Society of Chemistry’s dedicated page.