Molecular dynamics simulations applied to the determination of nuclear lifetimes from Doppler-broadened γ-ray line shapes produced in thermal neutron capture reactions

Abstract

Molecular dynamics simulation of slowing down of nuclei produced in thermal neutron capture reactions is used to deduce lifetime values of excited nuclear states in 36 Cl[τ=63±2 fs (E x=1.959 MeV) , 48±26 (2.49), 31±5 (2.68), 21±1 (2.86), 59±3 (3.60)], 49 Ti[29±2 (1.76), 79±4 (3.18), 16.2±0.7 (3.26)] , 54 Cr [112±22 (2.62), 10.3±0.5 (3.07), 24±2 (3.72)], 57 Fe [52±4 (1.63), 38±3 (1.73)] , 59 Ni [40±7 (2.89), 37±5 (3.18), 6.5±1.4 (4.14)], and 61 Ni [73±14 (2.12)] from Doppler-broadened γ-ray line shapes. It is characteristic for the line shapes that they are produced by emission of secondary γ-rays from nuclei recoiling at ultra-low velocities, below 10 5 m/s, the recoil energy being imparted to nuclei by emission of typically 5–10 MeV primary γ-rays. The novel method of analysis used in the deduction of the lifetime values is described. The relevance of interatomic potentials on the reliability of lifetime values is considered.