The present specification discloses a beam chopping apparatus, and more specifically, a helical shutter for an electron beam system that is employed in radiation-based scanning systems, and more specifically, a beam chopping apparatus that allows for variability in both velocity and beam spot size by modifying the physical characteristics or geometry of the beam chopper apparatus. The present specification also discloses a beam chopping apparatus which provides a vertically moving beam spot with substantially constant size and velocity to allow for substantially equal illumination of the target. In addition, the present specification is a beam chopping apparatus that is lightweight and does not cause an X-ray source assembly employing the beam chopper to become heavy and difficult to deploy.