Geometric Unsharpness (Ug)
Geometric unsharpness is the radiographic image blur caused by the finite size of the radiation source, calculated as Ug = F × t / d, where F is focal-spot size, t is object-to-film distance, and d is source-to-object distance.
Definition
Geometric unsharpness Ug limits the smallest detail resolvable on a radiograph. It is reduced by using a smaller focal spot, increasing the source-to-film distance, or minimizing the object-to-film distance.
Technical Context
ASME Section V specifies maximum allowable Ug values (e.g., 0.5 mm for material under 50 mm thick).
Related terms
- Source-to-Film Distance (SFD) — Source-to-film distance (SFD), also called focus-film distance (FFD), is the geometric distance between the radiation source focal spot and the film, controlling geometric unsharpness and radiation intensity at the film.
- Radiographic Sensitivity — Radiographic sensitivity is the smallest detail or thickness change reliably detectable in a radiograph, demonstrated by which IQI feature is visible — for example, 2-2T hole IQI or wire #10 wire IQI sensitivity.
- ASME Section V — ASME Section V (Nondestructive Examination) is the chapter of the ASME Boiler and Pressure Vessel Code that defines NDT methods, procedures, and personnel qualification requirements for examinations referenced by other ASME construction and in-service codes.
More physics terms
Back-Wall Echo · Beam Spread · Near-Field · Far-Field · Dead Zone · Shear Wave · Longitudinal Wave · Surface Wave · Lamb Wave · Mode Conversion
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.