Failure to Bond Rupture and Nuclear Recoil Following (n, γ) Activation

Following the absorption of a thermal neutron by 127I or 79Br, the neutron‐binding energy is frequently released in the form of a gamma‐ray cascade. As a result of partial cancellation of gamma‐ray momenta, a small fraction of the activated halogens will not receive sufficient recoil momentum to rupture from their parent compound. The gas‐phase failures to bond rupture following 127I(n, γ) 128I, and 79Br(n, γ) 80Br activation were found experimentally to be: CH3I—1.09, CD3I—0.68, CF3I—0.12, CH2I2—0.068, C2H5I—0.082, n‐C3H7I—0.66, i‐C3H7I—0.30, CH3Br—0.25, CD3Br—0.20, CH2Br2—0.12, CF3Br—0.11, CF2Br2—0.093, CHClBr2—0.087, CCl3Br—0.066, CHBr3—0.05, CBr4—0.03, C2H5Br—0.33, and 1,1‐C2H4Br2—0.17%. These data are correlated with the calculated recoil energies required for bond rupture (preceding article). Using as a basis the distribution of net gamma‐ray energies calculated by the random‐walk method for the 35Cl(n, γ) 36Cl process, the kinetic‐energy distributions of the dissociated 128I or 80Br are approximated. These data suggest that the extent of hot‐atom reaction of 128I or 80Br with CH4 should not depend upon the parent molecule from which the activated halogen dissociates