Polonium in the Earth's crust are not harmful. Polonium has been found in tobacco smoke from tobacco leaves grown with phosphate fertilizers. Because it is present in small concentrations, isolation of polonium from natural sources is a tedious process. The largest batch of the element ever extracted, performed in the first half of the 20th century, contained only (9 mg) of polonium-210 and was obtained by processing 37 tonnes of residues from radium production. Polonium is now usually obtained by irradiating bismuth with high-energy neutrons or protons. In 1934, an experiment showed that when natural Bi is bombarded with neutrons, Bi
Modulated neutron initiator the force of conventional explosives. The initiator used in the early devices, located at the center of the bomb's plutonium pit, consisted of a beryllium pellet, and a beryllium shell with polonium between the two. The pellet, 0.8 cm in diameter, was coated with nickel and then a layer of gold. The beryllium shell was of 2 cm outer diameter with wall thickness of 0.6 cm. The inner surface of that shell had 15 concentric, wedge-shaped latitudinal grooves and was, like the inner sphere, coated with gold and nickel. A small amount of polonium-210 (50 curies, 11 mg) was deposited