Abstract
The HPGe detector assembly of gamma-ray spectrometer cooled by Stirling cycle cryocooler is under consideration. Modal analysis based on the compiled dynamic model was carried out. The natural frequencies and modes shapes for HPGe detector with relative efficiency 15 % mounted by supports made from composite G-Etronax and CESTILENE HD 1000 were calculated by Solidworks simulation. The frequencies of the axial mode are in range of 200-600 Hz where electrical interferences caused by mechanical vibrations (so-called microphone noise) has a large impact on the resolution of spectrometer. It is shown that for cryostat cap the lowest natural frequencies determined by the thickness of input window lay in higher frequency range. The validity of the adopted model was confirmed by the experiments. The calculated natural frequencies of the detector assembly are compared to the harmonics of cryocooler’s vibration. The results obtained are useful to identify the interferences source in electrical circuits of spectrometer at its adjusting.
Highlights
The applying of High Purity Germanium (HPGe) detectors in Gamma-ray spectrometers assumes their cooling to cryogenic temperatures
Modal analysis of the HPGe detector assembly based on the compiled dynamic model was carried out
The natural frequencies and modes shapes for HPGe detector on supports and for cryostat cap were calculated by Solidworks simulation
Summary
The applying of High Purity Germanium (HPGe) detectors in Gamma-ray spectrometers assumes their cooling to cryogenic temperatures. Mechanical vibrations inherent in Stirling cryocoolers are the reason of electrical noise induced at the preamplifier input. In its turn the changes of the capacitances in input circuits of the preamplifier cause electrical interference. This microphone effect (the conversion of mechanical vibrations into electrical signals) reduces the final resolution of spectrometer [1,2,3,4,5,6,7]. Electronic controllers used for modern cryocoolers allow to change operating frequency within the certain limits. This fact allows to avoid the coincidence between frequencies of cryocooler vibration and natural modes of detector assembly with the aim to decrease it vibration.
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