Counting nucleon pairs

A simple method is used to count average numbers of different kinds of nucleon pairs within the Sp(4) seniority-like model which describesT=1 pairing modes of protons and neutrons. These numbers as well as the total strengths of pair-transfer processes clearly indicate that pn configurations are preferred in theN _p=N _n odd-odd systems. Presented at Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31, 1997.