A generator column assembly for the elution of a radioisotope, having a generator column container having a bottom wall defining a flow outlet aperture, an open top end, and a sidewall extending from the open top end to the bottom wall that defines an interior volume having a substantially cylindrical upper volume portion and a substantially cylindrical lower volume portion, the upper volume portion having a diameter that is greater than a diameter of the lower volume portion, and a closure cap assembly including a substantially cylindrical container cap defining a flow inlet aperture, the container cap being configured to be slidably received in the open top end of the generator column container.