Detection of nuclear materials: Features and functions of effective half-life

The delayed high-energy γ ray method is an approach used to detect the presence of nuclear materials. To study the features and functions of the effective half-life (EHL) in this method, a scenario where a beam of 14 MeV neutrons is used to irradiate a pure 238U indefinitely thin target was assumed. In this work, a population for study was built, consisting of the seven fission products that are the dominant contributors to the β-delayed γ rays with energies above 3 MeV. Based on this population for study, calculations were performed to trace the decay of the integral intensity of the γ rays above 3 MeV for a variety of beam-on intervals, to study the EHL at a variety of beam-off intervals, and to investigate the features and functions of the EHL. The study showed that the EHL has a feature that means that any measured EHL should fall within an appropriate range if nuclear material is present. Because of this feature, the EHL can be used as complementary evidence to confirm the presence of nuclear materials, on the precondition that a 'clear' spectral region of interest can be settled upon.