[en] The neutron self-powered detector (cobalt) is used to measure the power and neutron fluence in the nuclear reactors by putting it in the reactor for a long time intervals. So it is necessary to know the secondary currents which produced from reactor gamma-ray effect as a result of reactors post irradiation, so the study included in this project the experimental and theoretical parts. The experimental part is, measurements of the distribution of the vertical thermal neutron fluence in the wet channel Hg of tammuz-2 reactor. The theoretical part is computing the secondary currents, which effect on the original current which is produced from neutron and sensitive part of detector reaction, and to find its values to help quiet efficiency of neutron fluence measurements and power, the computer programme is writing for this purpose by depending on the cobalt detector dimension as a sample of computing. Hence the programme also is used to compute other self-powered detectors and the attention to the kind of sensitive part and dimensions. 14 tabs.; 26 figs.; 32 refs