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Szilard-Chalmers effect

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An effect discovered by L. Szilard (1898–1964) and T. A. Chalmers in 1934; it has been used to separate radioactive products in a nuclear reaction involving the absorption of a neutron and the emission of gamma rays. If a material absorbs a neutron and subsequently emits a gamma ray, the emission of the gamma ray causes the nucleus to recoil. Frequently, the recoil energy is sufficient to break the chemical bond between the atom and the molecule of which it forms part. Thus, although the atom that has absorbed the neutron is an isotope of the original atom it is in a different form chemically, enabling separation to take place. For example, if an aqueous solution of sodium chlorate (NaClO3) is subjected to bombardment by slow neutrons, the Cl37 is converted to Cl38, with many of the Cl38 atoms breaking from the chlorate and moving into the solution in the form of chloride ions. This is an example of a ‘hot atom’ reaction. The Cl38 can be precipitated out using silver nitrate.

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