Radiographic Testing · Field Calculators

Radiography Calculators

Geometric unsharpness, minimum SOD, source decay, and the inverse square law — built from the standard radiography formulas with ASME Section V limits where applicable.

Active Formula
Ug = (f · t) / SOD
01 · GEOMETRIC UNSHARPNESS

Compute Ug from source size, thickness, and SOD

A smaller source, thinner part, or longer source-to-object distance reduces geometric unsharpness. ASME Section V sets the maximum Ug by material thickness.
Geometric Unsharpness
—
—in
ASME Section V · Maximum Permitted Ug
Material ThicknessMax Ug (in)
Under 2″0.020
2″ through 3″0.030
Over 3″ through 4″0.040
Greater than 4″0.070

The highlighted row matches the entered thickness; the status badge above compares the computed Ug to that row's limit.

02 · MINIMUM SOD

Find the minimum source-to-object distance

Given the source size, part thickness, and the maximum permitted Ug, solve for the SOD that keeps unsharpness at or below the limit.
Minimum SOD
—in

Derived by rearranging Ug = (f · t) / SOD  →  SOD = (f · t) / Ug.

03 · SOURCE DECAY

Activity after N half-lives have elapsed

Radioactive sources decay exponentially. Each half-life cuts the activity in half. Use matching units (days or years) for both the half-life and elapsed time.
Activity after days
—Ci

A = A₀ · (½)N/T½. Choosing an isotope above auto-fills the half-life and switches the time unit.

04 · INVERSE SQUARE LAW

Intensity scales with 1 / distance²

Doubling the distance from a point source cuts the intensity to one quarter. Solve for the intensity at a new distance.
Intensity at D₂
—R/h

I₂ = I₁ · (D₁ / D₂)². Units of I₁ and I₂ match; units of D₁ and D₂ must match each other but can be different from the intensity unit.