Szilárd-Chalmers effect
The Szilard-Chalmers effect is used in radiochemistry , ie the chemistry of radioactive substances, to separate radioactive isotopes ( Szilárd and Chalmers, 1934).
In an (n, γ) -nuclear reaction (see neutron deposition ), a thermal (slow) neutron is absorbed by an atomic nucleus . The atomic nucleus of the newly formed isotope is in a highly excited state and emits a gamma quantum when it returns to the ground state . The atom is torn out of its previous bond in the original molecule by the associated recoil and enters into a new, different chemical bond in a suitable medium , so that the isotope formed - although its chemical properties are identical to the original isotope - from this can be isolated chemically.
discovery
After irradiating iodoethane (ethyl iodide) with natural 127 I with thermal neutrons, Szilard and Chalmers found a large part of the 128 I no longer chemically bound in the iodoethane, but as an iodide ion that can be extracted with water. The explanation found for this was that when the gamma quantum (4.8 MeV) is emitted, a recoil energy of about 100 eV is transferred to the emitting core. This breaks the CI bond because its binding energy is only 2.2 eV.
literature
- L. Szilard and TA Chalmers: Chemical separation of the radioactive element from its bombarded isotope in the Fermi effect . In: Nature . 134 , 1934, p. 462. doi : 10.1038 / 134462b0 .
Web links
- A. Wieghaus, S. Ritzel: Basic internship in nuclear chemistry WS 2002/2003: Szilard-Chalmers reactions , script
Single sources
- ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 143.