Development of a low-temperature germanium detector via mechanical cooling with a compact pulse-tube refrigerator

We have developed a new germanium (Ge) detector unit for hypernuclear γ-ray spectroscopy at J-PARC, which comprises a new Ge detector array Hyperball-J. A compact pulse-tube refrigerator is coupled to a coaxial Ge detector in order to achieve lower crystal temperatures as a means to increase radiation hardness. The obtained crystal temperature is 72 K, while an energy resolution is maintained at (FWHM) 3.1(1) keV for 1.33 MeV γ rays using a gate-integrated shaping amplifier (ORTEC 973U). Gain shifts with changing crystal temperature are also confirmed for the Ge detector.