in your element The unveiled states of americium Made under a cloak of wartime secrecy, yet announced in the most public of ways — a radioactive element that governments insist we take into our homes. Ben Still explains how element 95 is one of real contradiction.
he Manhattan project gave rise to the that governments insist we keep in our
world’s first atomic bombs, which relied homes. AmO2 is a key component of smoke Ton the chain reaction of two particular detectors: around 0.3 μg of the isotope 241Am fissile isotopes of uranium and plutonium. sits inside a sealed metal box at the heart of 235 U, having been enriched from its natural the device, spitting out alpha radiation. The abundancy, was used for the first atomic small electric charge arising from ionization weapon. Little Boy, as it was codenamed, was of air by the alpha radiation lets the detector dropped on Hiroshima on the 6th of August, know everything is just fine. However, large 1945. Three days later the second atomic smoke particles absorbing the alpha radiation bomb, Fat Man, was detonated over Nagasaki: reduce the amount of ionization and thus for this bomb, high densities of neutrons electric current, which triggers the detector in nuclear ‘breeder’ reactors transformed to sound the alarm. abundant 238U into 239Pu. Americium is most commonly trivalent It was realized early in the project that in solution, with tetravalency also frequent if the 239Pu in the Fat Man bomb were to be in solids such as the oxide mentioned above. LIBRARY PICTURE & SOCIETY SCIENCE IMAGES SSPL/GETTY transportable and only reach criticality (the Ernest Lawrence (third from the left) and his team However, states +2 to +7 have been reported point at which nuclear chain reaction can in front of the 60-inch cyclotron that produced experimentally, and even Am(viii) has been be self-sustained) when desired, then any the first measureable sample of americium. suggested as being potentially accessible — and all impurities had to be carefully studied albeit somewhat speculatively4. and understood1. It was the task of those Although the radioactivity of plutonium working in the Metallurgical Laboratory 1944 this observation was the first confirmed is used to provide thermonuclear energy (Met Lab) at the University of Chicago sighting of element 95 (ref. 2). Further to deep space exploration satellites, there (now the Argonne National Laboratory) to experiments produced other isotopes, of are ever tighter regulations around its sale identify and analyse the properties of these which the 24395 isotope was found to be the and use on account of its fissile nature. new synthetic elements. most stable. The very existence of the element Americium on the other hand is non-fissile, Some isotopes were notoriously difficult was classified and would remain secret until which is enticing European space scientists to to extract and so scientists at Berkeley the war came to a close. consider using it as a plutonium alternative Laboratory used Ernest Lawrence’s atom Once the cloak of secrecy was shed in for future missions5. smasher — a 60-inch cyclotron — to create late 1945, the discovery of elements 95 and Ever since its discovery was announced them in a controlled environment. Samples 96 was announced to the world in an on live radio, element 95 has found its of 238U and 239Pu were bombarded with high- unexpected way. Their unveiling was planned way into our homes, and it could soon be energy alpha particles (helium nuclei) to for the American Chemical Society’s national powering our exploration to the furthest recreate environs present in breeder reactors. meeting, scheduled for the 16th of November. reaches of the cosmos. ❐ With 239Pu this process resulted in element 96, Instead, Glenn T. Seaborg told a national now named curium, whereas with 238U it audience live on radio during a show called BEN STILL, author of The Secret Life of the produced element 95. Using this method, Quiz Kids five days before the conference3. Periodic Table, is at the School of Physics the Berkeley scientists were able to obtain a He was asked by a child contestant if any and Astronomy, Queen Mary University of large enough quantity of both new elements other elements, aside from plutonium and London, Mile End Road, London E1 4NS, UK. to enable the team at the Met Lab to identify neptunium, had been discovered at the Met e-mail: [email protected] their properties. Lab during the war. Seaborg disclosed the Twitter: @benstill After irradiating238 U with 4He nuclei they discovery of elements 95 and 96, telling his discovered a hitherto unseen low-energy young audience “now you’ll have to tell your References emission — the β-decay of 241Pu. This process, teachers to change the 92 elements in your 1. Nichols, K. D. The Road to Trinity(William Morrow transforming one neutron into a proton, schoolbook to 96 elements”. and Company, 1987). 2. Seaborg, G. T., James, R. A. & Morgan, L. O. The New Element resulted in an element with atomic number Element 95 was named americium (Am) Americium (Atomic Number 95) (Oak Ridge, 1948); 95 and mass number 241. In the autumn of by Seaborg and his team2, giving recognition http://go.nature.com/2jZREao to the location of its discovery, but also 3. The Quiz Kids(Niels Bohr Library & Archives, 11 November 1945). 4. Nikolaevskiiа, V. B. & Shilov, V. P. Radiochemistry 55, 261–263 (2013). mirroring its lanthanide opposite number: 5. O’Brien, R. C., Ambrosi, R. M., Bannister, N. P., Howe, S. D. & europium. It is the only radioactive element Atkinson H. V. J. Nucl. Mater. 377, 506–521 (2008). U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn 296 NATURE CHEMISTRY | VOL 9 | MARCH 2017 | www.nature.com/naturechemistry ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.