Polonium initiator was classified until the 1960s. The Atomic Energy Commission and the Manhattan Project funded human experiments using polonium on five people at the University of Rochester between 1943 and 1947. The people were administered between of polonium to study its excretion. Polonium is a very rare element in nature because of the short half-life of all its isotopes. Po, Po, and Po appear in the decay chain of U; thus polonium can be found in uranium ores at about 0.1 mg per metric ton (1 part in 10), which is approximately 0.2% of the abundance of radium. The amounts
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