Keychain Pa Protactinium.

<div>   </div> <div> <strong> Atomic number <span class = "Apple-tab-span" style = "white-space: pre;"> </span>     91 </strong> </div> <div> <strong> Atomic mass <span class = "Apple-tab-span" style = "white-space: pre;"> </span>       231.04 </strong> </div> <div> <strong> Density, kg / m? <Span class = "Apple-tab-span" style = "white-space: pre;"> </span> & nbsp ;   15400 </strong> </div> <div> <strong> Temperature </strong></div> <div> <strong> melting, ° С <span class = "Apple-tab-span" style = "white- space: pre; "> </span>         1840 </strong> </div> <div>   </div> <div> Protactinium is a shiny silvery white, highly radioactive metal. & Nbsp; </div> <div> In 1913, Casimir Fajans and Oswald Helmut Göring discovered the protactinium isotope in the decay products of uranium with a half-life of about 1 min, named because of its short life time "breviy" (from the Latin brevis - "short" or "short"). Then Black, Hahn and Meitner discovered the similarity of protactinium to tantalum. </div> <div> In 1918 Hahn and Meitner in uranium tar and independently of them Soddy and Crenston discovered the long-lived isotope protactinium, so named because it was the predecessor of anemones. </div> <div> Due to the low content in the earth's crust (content of the Earth's mass is 0.1 billionth of a percent) and extreme toxicity, the element has a very narrow application - an additive to nuclear fuel. The content of protactinium per ton of uranium is 0.34 g. </div> <div>   </div>