Radiographic Testing Exposure Time Calculator for Ir-192 on 2-Inch Steel
Formula
t = (Target Dose × SFD²) / (Activity × Gamma Constant × 60)
Governing Standard
ASME V Article 2 and EN ISO 17636-1 — Radiographic Testing
Required Inputs
- Source Type (Ir-192 or Co-60)
- Activity in Curie (Ci)
- Source-to-Film Distance (SFD) in mm
- Film Speed Factor (1.0 for D7 standard)
Output
Exposure Time in minutes and Safe Boundary Distance in meters
Notes
For Ir-192 at 50 Ci activity, SFD = 700mm, D7 film (speed factor 1.0): gamma constant = 0.48 R/h/Ci at 1m. Dose rate at 1m = 50 × 0.48 = 24 R/h. Target dose for D7 film ≈ 2.0 R. Exposure time = (2.0 × 700²) / (50 × 0.48 × 60) = 980,000 / 1,440 = 680 seconds = 11.3 minutes. Safe boundary (2 mR/h): distance = √(24/0.002) = 109 meters.
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