James Chadwick - awarded the 1935 Nobel Prize for his discovery of the neutron

SIR JAMES CHADWICK

V: James Chadwick was born in Manchester in 1891. He attended Manchester Grammar School and then graduated with honours in Physics, from the University of Manchester in 1908. he continued work at his university on radioactivity under Rutherford from 1911 to 1913 when he received his MSc. He was awarded the 1935 Nobel Prize for his discovery of the neutron.

R: In the period 1930-32 Bothe and the Joliot Curies found that when certain light elements such as beryllium were bombarded with alpha particles, some sort of radiation occurred. They did not reach a satisfactory identification for this radiation, but Chadwick repeated the experiments and in 1932 suggested a consistent interpretation in terms of the NEUTRON, a neutral particle of approximately the mass of a proton.

V: Chadwick proposed that alpha particles knocked neutrons out of the nuclei of beryllium atoms and that these neutrons in turn knocked protons out of paraffin (rich in hydrogen atoms). Energy measurements confirmed Chadwick’s suggestion; using data on different targets he was able to calculate the mass of the neutron.

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R: Unaffected by electric charges, the neutron can slip into a nucleus; it proved to be the most useful particle for initiating nuclear reactions. An important type, nuclear fission, was discovered by Hahn and Meitner in 1938. The concept of an atomic nucleus built of protons and neutrons explained why, when the elements are arranged in order of increasing mass, the atomic mass increases more rapidly than the atomic number. Further, different isotopes of a particular element all contain the same number of protons; they differ in mass by having a different number of neutrons.

LISE MEITNER & OTTO HAHN

V: Lise Meitner was born in 1878 and Otto Hahn in 1879. together with Fritz Strassmann they were the first to recognise that the uranium atom actually split under the bombardment of neutrons. Meitner studied Radioactivity at the University of Berlin. It was at this time that she met Otto Hahn and they began a long journey into radioactivity. As their experience progressed, Meitner and Hahn began researching the end of the periodic table. They began to search for the ‘parent’ element of actinium, but this was interrupted by WW II. In 1917 she and Hahn announced the discovery of Protactinium, the parent element of Actinium.

R: She discovered ‘nuclear fission’ by instructing Hahn to bombard uranium with neutrons, he found that Barium had been formed, he could not explain how it happened. Meitner discovered that the uranium nucleus had split, rather than have small particles chipped off. She realised that if one fragment was barium then the other was krypton. A large amount of energy had also been released. Meitner was the first person in the world to explain what had happened and she was able to calculate the energy realease using Einstein’s famous equation: E=mc2. These discoveries were confirmed around the world in 1939,but in 1946 Hahn was awarded the Nobel Prize for Physics and Meitner was ignored.

V: Otto Hahn was born in 1879in Frankfurt. He studied chemistry in Munich. He met Meitner in 1907 in Berlin. Along with his discovery of Protactinium his most spectacular discovery came at the end of 1938. He discovered the fission of uranium and thorium in medium heavy atomic nuclei. He continued his investigation on the proof and separation of many elements and kinds of atoms which arise through fission until 1944.

R: Otto Hahn and Lise Meitner both died in 1968.