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To verify nuclear weapon treaties, such as CTBT the ability to scientifically monitor treaty violations is of importance. One tool for monitoring nuclear weapons testing is the use of gamma ray spectrometry. A calibration on a multi detector element coincidence gamma spectrometer setup was performed from previously gathered experimental data. Data from one calibration sample and a blank sample were analyzed in this project. The first part consisted of energy, full width half maximum (FWHM) and efficiency calibrations, for each of the detectors. Spectra were created, showing the results in the different detectors. From the spectra, several radionuclides were identified, both background nuclides and nuclides from the calibration sample. To each peak, a Gaussian shaped curve was numerically fitted and the parameters were used to perform the calibrations. Efficiencies were calculated for the individual peaks, whereas the energy and FWHM calibrations resulted in linear relationships. During the second part of this project, coincident gamma-rays were investigated. The efficiency for a coincident decay in each detector pair was calculated. This was compared with the product of the singular efficiencies, and a correction term was introduced. Furthermore, the signal to noise ratio was compared for spectra created with different data sorting methods.