  The design and construction of a recoil detector for the measurement of
recoil protons of antiproton-proton elastic scattering at scattering angles
close to 90$^{\circ}$ are described. The performance of the recoil detector has
been tested in the laboratory with radioactive sources and at COSY with proton
beams by measuring proton-proton elastic scattering. The results of laboratory
tests and commissioning with beam are presented. Excellent energy resolution
and proper working performance of the recoil detector validate the conceptual
design of the KOALA experiment at HESR to provide the cross section data needed
to achieve a precise luminosity determination at the PANDA experiment.
