Nuclear event zero-time calculation and uncertainty evaluation

It is important to know the initial time, or zero-time, of a nuclear event such as a nuclear weapon’s test, a nuclear power plant accident or a nuclear terrorist attack (e.g. with an improvised nuclear device, IND). Together with relevant meteorological information, the calculated zero-time is used to help locate the origin of a nuclear event. The zero-time of a nuclear event can be derived from measured activity ratios of two nuclides. The calculated zero-time of a nuclear event would not be complete without an appropriately evaluated uncertainty term. In this paper, analytical equations for zero-time and the associated uncertainty calculations are derived using a measured activity ratio of two nuclides. Application of the derived equations is illustrated in a realistic example using data from the last Chinese thermonuclear test in 1980.

► Nuclear event zero-time can be calculated using radionuclide activity ratios.
► Analytical equations for zero-time and associated uncertainty are derived.
► Calculated data may be used to help locate the origin of a nuclear event.