We describe the development of a miniaturized HPGe gamma-spectrometer for space applications. The spectrometer is designed around a 170 cm3 intrinsically pure n-type Ge crystal in the closed-end coaxial configuration cooled by a miniature Sterling cycle electric cooler. The complete assembly has a mass of 2.9 kg and consumes 6.6 W under normal operation. The spectrometer was tested in a specially designed chamber which simulates the space environment. FWHM energy resolutions of 2.9 keV and 4.0 keV were achieved at 122 keV and 1332 keV, respectively. With the cooler switched-off, these improved to 2.0 keV and 3.0 keV, respectively, indicating that induced noise from the mechanical vibrations of the cooler accounts for about half the resolution.

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.

We report on the development of a miniaturized HPGe gamma-spectrometer for space applications. The instrument is designed around a 158 cm3 intrinsically pure Ge crystal in the closed-end coaxial configuration, cooled by a Thales RM3 miniature Stirling cycle electric cooler. To compensate the noise induced by the mechanical cooler the digital procession of the spectrometric signals with low frequency reject filter (LFR) is applied. The complete spectrometer assembly has a mass of 3.1 kg and consumes less than 10 W under working operation. The spectrometer was tested under a number of operating conditions in a specially designed chamber, which simulates the space environment. With the mechanical cooler switched off, FWHM energy resolutions of 1.5 keV and 2.2 keV were obtained at 122 keV and 1333 keV, respectively, at the nominal operating temperature of 90 K. When the cooler was switched on the energy resolutions degraded to 2.5 keV and 4 keV respectively. However, with the LFR filter switched in, the resolutions improved significantly to 1.8 keV and 2.4 keV.

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