A detailed study of alpha interactions on the passivation layer on theend-plate of a true-coaxial high-purity germanium detector is presented. Theobservation of alpha events on such a surface indicates an unexpectedly thinso-called "dead layer" of less than 20 {\mu}m thickness. In addition, theinfluence of the metalisation close to the end-plate on the time evolution ofthe output pulses is discussed. The results indicate that alpha contaminationcan result in events which could be mistaken as signals for neutrinoless doublebeta decay and provide some guidance on how to prevent this.
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