The invention relates to an apparatus for ejecting a fluid, having a housing comprising a cartridge retainer (50, 52) configured to hold a fluid containing cartridge (90, 100) and further comprising a cap connection part for removably attaching thereto a cap (18), having a sensor (502,) configured to determine whether the cap (18) is attached to the connection part, and having a control unit configured to measure a quantity being a measure for the radiation load on a cartridge in the cartridge retainer, wherein the control unit is further configured to cause a control step to be performed once the quantity exceeds a predefined threshold value. The invention further relates to a system comprising such an apparatus and a cap (18) configured to be removably attached to the connection part of the apparatus and to a method for controlling such an apparatus or such a system comprising the steps of measuring a quantity being a measure for the radiation load on a cartridge in the cartridge retainer； and performing a control step once the quantity exceeds a predefined threshold value.
