Bombardment Division

Nuclear fission is a process in which a heavy nucleus—usually one with a nucleon number of two hundred or more—separates into two nuclei. Usually the division liberates neutrons and electromagnetic radiation and releases a substantial amount of energy. The discoveiyi of nuclear fission is credited to Otto I lahn and Fritz Strassman. In the process of bombarding uranium with neutrons in the late 1930s, they detected several nuclear products of significantly smaller mass than uranium, one of which was identified as Ba. The theorectical underpinnings that exist to this day for nuclear fission were proposed by Lise Meitner and Otto Frisch. Shortly after Hahn and Strassman s discovery. 

When heavier nuclei are bombarded by slow neutrons, the nuclei of lighter elements are formed. Besides the energy released, several neutrons are emitted. The disintegration of a heavier nucleus into lighter nuclei by neutron bombardment is called nuclear fission (nuclear division). 

Aunt and nephew conferred by telephone further over the weekend to prepare not one but two papers for Nature, a joint explanation of the reaction and Frisch s report of the confirming evidence of his experiment. Both reports— Disintegration of uranium by neutrons a new type of nuclear reaction and Physical evidence for the division of heavy nuclei under neutron bombardment —used the new term fission. Frisch finished the two papers on Monday evening, January 16, and posted them airmail to London the next morning. Since he and Bohr had already discussed the theoretical paper and since the experiment only confirmed the Hahn-Strassmann discovery, he did not hurry to let Bohr know. 

Frisch, Otto. 1939. Physical evidence for the division of heavy nuclei under neutron bombardment. Nature 143 276. 

On the morning of 19 February 1945 the 4th and 5th Marine Divisions landed on the beaches of the island of Iwo Jima in the face of the heaviest enemy beach resistance since Tarawa. The bombardment of the island that preceded the attack was the heaviest of the Pacific war, one that benefited from the experiences of the island assaults that had taken place before. Three of the five mortar units, Numbers i, 2, and 5, took part in the actual assault phase. 

During the mid-1930s, scientists bombarded uranium (Z = 92) with neutrons in an attempt to synthesize transuranium elements. Many of the unstable nucUdes produced were tentatively identified as having Z > 92, and eventually, one was shown to be an isotope of barium (Z = 56). The Austrian physicist Lise Meitner and her nephew, Otto Frisch, proposed that barium resulted from the splitting of the uranium nucleus into smaller nuclei, a process that they called fission as an analogy to cell division in biology. Element 109 was named meitnerium in honor of this extraordinary physicist. 

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