NRNDT Radio LU

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Geometric unsharpness

Geometric unsharpness depends on focal spot size, object-to-film distance and source-to-object distance. Calculate Ug, or the minimum source-to-object distance for a given Ug.

mm
Effective focal spot in the useful direction.
mm
Part thickness on the film side, or the actual object-to-film distance.
mm
Must be greater than the object-to-film distance.

Geometric unsharpness—mm
Mode
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Source-to-film distance
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Method

Ug = f × b / (SOD − b)

SOD = f × b / Ug_max + b

  • f — effective focal spot size in mm
  • b — object-to-film distance in mm
  • SOD — source-to-object distance in mm
  • Ug — geometric unsharpness in mm

The ratio SOD / b is the geometric magnification ratio. If SOD ≤ b the object sits at or behind the source: the calculation is meaningless and the tool shows no value.

Indicative result — check it against your authorisation and your dosimetry.