A new method for author groups formation and decay processes is proposed. With the help of a special mathematical model time distribution of authors and their publications was established and group productivity, composition and stability, annual change of the total number of short-term and long-term authors, their renovation etc. as well as the time dependence of these quantities was determined. Particularities of activity of authors working in nuclear physics are investigated. It is shown that the most rapid development in this field took place in the pre-war years, it was at high level up to 1960 and then began to decrease. The method used permits to forecast the development of science and to analyse the activity of author units in particular scientific centers.