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

Abstract
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.