Development of digital coincidence counting method and its application in 4pi-beta-gamma counting system on certain radioisotopes having complex decay scheme

The methods of data acquiring and processing in the 4πβ-γ coincidence counting systems for radionuclide standardization have been employed by using analogue electronic modules for decades. Since the supply and maintenance of these modules are costly, the need for the digital data acquiring and processing systems which are faster, more flexible and more reliable have been arised in parallel to the new advancements in radiation measurement systems. Achieving the signal parameters from the detector of a 4πβ-γ coincidence counting system by using a digital card and analyzing these signal parameters offline by using computer programs became an easy and innovative alternative method for the conventional analogue systems. In this thesis, a unique software has been developed to be used as data analysis method of the 4πβ-γ coincidence counting system setup in the Radionuclide Metrology Laboratories of Turkish Atomic Energy Authority (TAEK) for absolute activity standardization. This real-time coincidence counting software includes coincidence and anticoincidence methods. Activity calculations have been performed using unique algorithms of these methods. The validation of the software were done by determining the activity values of the standart radioactive solutions including 60Co, 133Ba, 152Eu and 166mHo radionuclides separately. Some amount of radioactive solutions were used as the source and then measured in the 4πβ-γ coincidence counting system. The data achieved from the counting system were analyzed in the software. The activity values of 60Co and 133Ba, which have relatively simple decay schemes, and of 152Eu ve 166mHo, which have relatively much more complicated decay schemes, have been determined by both coincidence and anticoincidence methods in a good agreement. The relative bias values between the two methods are found as 0.3% for 60Co, 0.18% for 133Ba, 0.1% for 152Eu and 0.08% for 166mHo. In addition, the Monte Carlo simulation of the 4πβ-γ coincidence counting system was performed, and the response functions of NaI detector for 60Co, 133Ba, 152Eu and 166mHo are determined as the detector efficiencies. The efficiency values and the experimental count rates of 60Co, 133Ba, 152Eu and 166mHo are used to calculate the activities of these radionuclides. When the activity values of these radionuclides determined by the coincidence method, anticoincidence method and Monte Carlo method were compared, it is found that the results agree well with each other within at most 2.5% relative bias. The developed digital coincidence software is now ready to be applied to the measurements of all radionuclides having simple or complicated decay schemes in the 4πβ-γ coincidence counting system. This primary radioactivity measurement system, which is used in world's leading radioactivity measurement laboratories, has become availbale in TAEK Radionuclide Metrology Laboratories as a result of this thesis study.