Development of Gamma-Ray Spectroscopy Techniques for Fundamental and Applied Research

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Thesis type
(Thesis) M.Sc.
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The subject of this thesis is the methodology used to characterize high-purity Germanium (HPGe) detectors used for gamma-ray spectroscopy. To this end results of the acceptance tests performed on Gamma-Ray Infrastructure For Fundamental Investigation of Nuclei (GRIFFIN) detectors completed at the SFU Nuclear Science Laboratory (SFU-NSL) are provided. GRIFFIN is a state-of-the-art HPGe gamma-ray array for decay spectroscopic studies at TRIUMF, Vancouver, BC. GRIFFIN's efficiency allows decay spectroscopy studies at TRIUMF to be extended deeper into regions far from stability.Individual GRIFFIN detectors were sent to SFU-NSL for testing purposes. To accommodate these detectors, an automatic cooling system and testing station with a digital and an analog data acquisition (DAQ) systems was set up. The digital DAQ was used for energy resolution and efficiency tests, the analog DAQ was used to examine the timing resolution of each crystal with respect to a BaF₂ scintillator. Based on the results discussed here, all 16 GRIFFIN detectors were accepted by the end of 2014. The GRIFFIN array is now complete and in operation.Several additional investigations of the GRIFFIN clover detector performance have been undertaken. Digital timing resolution with respect to a BaF₂ scintillator has been measured using 14-bit, 100 MHz digitizers. The improvement in photopeak efficiency via energy add-back of gamma rays which scatter between the four crystals of a clover has been measured with standard calibration sources. GRIFFIN detectors have also been used in conjunction with a wall of 24 CsI detectors to measure the angular correlation between the α particle and the gamma ray emitted in the decay of ²⁴¹Am.As a part of this thesis a novel method is proposed for establishing the absolute efficiency calibration of a HPGe detector including the confidence interval in the energy range of ~80-3450~keV. The calibrations were accomplished with the ¹³³Ba, ⁶⁰Co, ⁵⁶Co and ¹⁵²Eu point-like radioactive sources with only the ⁶⁰Co source being activity calibrated to an accuracy of 2% at the 90% confidence level. The proposed fit function accounts for scaling of the data taken with activity uncalibrated sources to the data taken with the high accuracy activity calibrated source.
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Supervisor or Senior Supervisor
Thesis advisor: Starosta, Krzysztof
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