In gamma-ray spectrometry with germanium detector, the summing effects have to be taken into account at low source detector distance. The peaks due to coincidence summing of X+X, X+gamma, gamma+gamma rays can complicate the spectrum obtained by this type of detector and significantly change the counting rates of single peaks. There is theoretical model developed for coincidence summing of X- and gamma-rays for radionuclides with complex decay schemes. This model enables to write equations for single peaks, the coincidence sum peaks and the total count rate. The efficiencies of detection and the activity are the unknowns in the count rate equation system. They can be determined by simultaneously finding the roots of the equation system. The theory was initially applied to the Ce-139 decay (Nuclear Instruments and Methods in Physics Research A 582 (2007) 592–602) and I try to do the same thing for Co-60! If anybody interesting for subject and for discussion, I can send him some reference and some of my work (this is my master thesis). Of course, I have some doubts about my work and some discussion will be helpful!