  The ePix detector family provides multiple variants of hybrid pixel detectors
to support a wide range of applications at free electron laser facilities. We
present the results of a systematic study of the influence of radiation induced
damage on the performance and lifetime of an ePix100a detector module using a
direct attenuated beam of the EuXFEL at 9 keV photon energy and an average
power of 10 $\mu$W. An area of 20 x 20 pixels was irradiated with an average
photon flux of approx. 7 x $10^{9}$ photons/s to a dose of approximately
760$\pm$65 kGy at the location of the Si/SiO$_2$ interfaces in the sensor. A
dose dependent increase in both offset and noise of the ePix100a detector have
been observed originating from an increase of the sensor leakage current.
Moreover, we observed an effect directly after irradiation resulting in the
saturation of individual pixels by their dark current. Changes in gain are
evaluated one and half hours post irradiation and suggest damage to occur also
on the ASIC level. Based on the obtained results, thresholds for beam
parameters are deduced and the detector lifetime is estimated with respect to
the requirements to the data quality in order to satisfy the scientific
standards defined by the experiments. We conclude the detector can withstand a
beam with an energy up to 1 $\mu$J at a photon energy of 9 keV impacting on an
area of 1 mm$^2$. The detector can be used without significant degradation of
its performance for several years if the incident photon beam intensities do
not exceed the detector's dynamic range by at least three orders of magnitude.
Our results provide valuable input for the operation of the ePix100a detector
at FEL facilities and for the design of future detector technology.
