  We present an improved statistical method for calculation of mean lifetime of
nuclei in a decay chain with uncertain relation between mother and daughter
nuclei. The method is based on formation of time distribution of intervals
between mother and daughter nuclei, without trying to set the exact
mother-daughter nuclei relationship. If there is a coincidence of mother and
daughter nuclei decays, sum of these distributions has flat term on which an
exponential term is superimposed. Parameters of this exponential function allow
lifetime of daughter nucleus to be extracted. The method is tested on Monte
Carlo simulation data.
