  A new ionisation chamber for alpha-spectroscopy has been built from
radio-pure materials for the purpose of investigating long lived alpha-decays.
The measurement makes use of pulse shape analysis to discriminate between
signal and background events. The design and performance of the chamber is
described in this paper. A background rate of ($10.9 \pm 0.6$) counts per day
in the energy region of 1 MeV to 9 MeV was achieved with a run period of 30.8
days. The background is dominantly produced by radon daughters.
