On August 6, 1945, a 10-foot-long (3 meters) bomb fell from the sky over the Japanese city of Hiroshima.
Less than a minute later, everything within a mile of the bomb's detonation was obliterated.
U-238 decays very slowly, its half-life being about the same as the age of the Earth (4500 million years).This means that it is barely radioactive, less so than many other isotopes in rocks and sand.Natural uranium as found in the Earth's crust is a mixture largely of two isotopes: uranium-238 (U-238), accounting for 99.3% and uranium-235 (U-235) about 0.7%.The isotope U-235 is important because under certain conditions it can readily be split, yielding a lot of energy.Helium is an inert noble gas with the chemical symbol He and the atomic number 2.
Its boiling and melting points are the lowest of any known element.
Early chemists had difficulty separating similar elements from each other.
Elements with similar properties can only be told apart with tests not available before the eighteenth century.
The mixture has properties different from those of the individual metals.
The first printing presses (dating back to the 1450s) held type made of bismuth alloys.
It was officially discovered in 1895 by two Swedish chemists, Per Teodor Cleve and Nils Abraham Langlet.