Radium seventh of a gram of radium. One kilogram of the Earth's crust contains about 900 picograms of radium, and one liter of sea water contains about 89 femtograms of radium. Radium was discovered by Marie Sklodowska-Curie and her husband Pierre Curie on 21 December 1898, in a uraninite (pitchblende) sample. While studying the mineral earlier, the Curies removed uranium from it and found that the remaining material was still radioactive. They separated out an element similar to bismuth from pitchblende in July 1898, that turned out to be polonium. They then separated out a radioactive mixture consisting mostly of two
Modulated neutron initiator particle bombardment, the beryllium atoms emit neutrons at a rate of about 1 neutron each 5–10 nanoseconds (See Beryllium#Nuclear properties). These neutrons trigger the chain reaction in the compressed supercritical plutonium. Placing the polonium layer between two large masses of beryllium ensures contact of the metals even if the shock wave turbulence performs poorly. The 50 curies of polonium generated about 0.1 watts of decay heat, noticeably warming the small sphere. The grooves in the inner surface of the shell shaped the shock wave into jets by the Munroe effect, similar to a shaped charge, for fast and thorough mixing