time known as supramolecular synthons.
Système International d’Unités
See si units.
Szilard–Chalmers effect 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 sufÜcient 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 (NaClO 3 ) is subjected to
bombardment by slow neutrons, the
Cl
37 is converted to Cl
38 , with many
of the Cl
38 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 Cl
38 can be precipitated
out using silver nitrate.
Système International d’Unités
516
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