Theory for the Szilard-Chalmers Reaction

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As is shown in the discussion of recoil energies in thermal n-capture reactions, chemical bounds can be broken due the recoil energy caused by the prompt γ-emission. This will lead to the creation of free radicals, which is very reactive. Therefore, a long list of new componds can be formed during n capture.

In 1934 L. Szilard and T. A. Chalmers showed that when Ethyliodide is irradiated with thermal neutrons, a large fraction of the radioactive nuclei created in the process will be present as free iodine atoms or iodine ions.

The bond breakage can typically lead to the following reacions:

[math]1) \quad C_2H_5 \, ^{127}\!I + ^{128}\!I \rightarrow C_2H_5 \cdot + ^{127}\!I \cdot + ^{128}\!I \cdot[/math]

[math]2) \quad ^{127}\!I \cdot + ^{128}\!I \cdot \rightarrow ^{127}\!I ^{128}\!I[/math]

[math]3) \quad C_2H_5 \cdot + ^{128}\!I \cdot \rightarrow C_2H_5 ^{128}\!I[/math]

[math]4) \quad C_2H_5 ^{127}\!I + ^{128}\!I \cdot \rightarrow C_2H_5 ^{128}\!I + ^{127}\!I \cdot[/math]

[math]5) \quad C_2H_5 ^{127}\!I + ^{128}\!I \cdot \rightarrow CH_2 ^{127}\!I CH_2 ^{128}\!I + H \cdot[/math]

[math]6) \quad C_2H_5 ^{127}\!I + ^{128}\!I \cdot \rightarrow CH_2 ^{127}\!I CH_3CH ^{127}\!I ^{128}\!I + H \cdot[/math]

[math]7) \quad ^{128}\!I \cdot + H \cdot \rightarrow H^{128}I[/math]

These reactions are listed according to diminising kinetic energy on the reaction products. Reaction 3) to 6) represent organically bound iodine. This part is named the retention. It denotes radionuclei which cannot easily be separated from the inactive iodine.

The substitutions reactions 5) and 6) represent a method for radio labeling a compound.

The reactions 2) and 7) represent ways to produce inorganic iodine.

The Szilard-Chalmers Reaction