Szilard Chalmer's Reaction

Szilard Chalmer's Reaction

Szilard and Chalmers discovered in 1934 a new way of separating the radioisotope product of (n, y) reactions. They found that when ethyl iodide is irradiated by slow neutrons in presence of water, most of the recoil ¹²⁸I atoms following bond rupture readily passes into the aqueous phase as ¹²⁸I⁻ ions, thus separating the isotope ¹²⁸I free from the bulk of the inactive isotope ¹²⁸I which remains in organic phase bound to the C-atoms in the parent molecule.
The inorganic yield can be greatly increased if some I⁻ ions in the form of KI are initially added as a carrier. Thus, a large fraction of the radio isotope formed is separated into the water layer in a state of high specific activity. If no KI is added, the resulting product is carrier free. This is called Szilard Chalmer's reaction. Substances best suited for this mode of radio isotope separation are organic chloro-, bromo-, and iodo- compounds, stable complexions, some oxy anions and some organo metallic compounds as As Ph₃BiPh₃, PbPh₄, ferrocyanide etc.
The most common nuclear reaction occuring with most elements is of the (n,γ) type. When the nucleus of a target atom, like ¹²⁷I capture a slow neutron it forms an isotope of one mass number higher.
¹²⁷I + n → ¹²⁸I*
The product nucleus is in the excited state, shown by the sterisk mark. In most cases, the excited nucleus returns to the ground state immediately, the excitation energy being emitted as one or more γ photons.
¹²⁸I* → ¹²⁸I + γ
So, the complete reaction is given as-
¹²⁷I + n ---(n,γ)→ ¹²⁸I
So, in the (n,γ) reaction, the nucleus recoils when γ is emitted. Often recoil energy is greater than bond energy leading to breaking of bonds.

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