To obtain uniform density (+/-0.10 OD) over the film, the X-ray beam should be oriented relative to the bucky grid and film as:

• A. Parallel to bucky grid and centered
• B. Perpendicular to bucky grid and offset
• C. Perpendicular to bucky grid and centered
• D. Parallel to bucky grid and offset

Answer: (C)

Uniform density on the film comes from aligning the X-ray beam so it passes cleanly through the grid and onto the film without angle or edge effects. The bucky grid is made of alternating lead strips and gaps; if the beam isn’t perpendicular to the grid, the lead strips can absorb more photons on one side, creating a density gradient (grid cutoff). Centering the beam on the grid ensures the exposure is symmetric across the field and matches the grid’s focal geometry, so the X-ray photons are attenuated evenly throughout the film. When the beam is perpendicular and centered, scatter is effectively managed by the grid and the film receives a uniform exposure, achieving the desired density within ±0.10 OD. Tilting or offsetting the beam relative to the grid disrupts this balance and leads to nonuniform density.