Gamma ray spectroscopy is a technique used to study the energy spectra of gamma rays. In this work measurements were performed with a planar and a coaxial high purity germanium (HPGe) detector. The energy and efficiency calibration was performed for both detectors using radioactive samples with known composition and activities. Using the energy and efficiency calibrations, the activity of 7Be and 127Cs were determined in samples created by nuclear reactions. These can be used later to determine the reaction cross section.