Calculator
Gamma exposure time
Exposure time needed to reach a given film density, from source activity, penetrated thickness and source-to-film distance.
Exposure timeseconds
- Duration
- —
- Activity in TBq
- —
- Dose rate at that distance
- —
Method
T = factor × F × density^1.42 × 2^(t/13) × d² / A × 60
- T — exposure time in seconds
- factor — film factor (dimensionless)
- F — isotope exposure factor (34 for Ir-192, 85 for Se-75, 4 for Co-60)
- density — density in g/cm³
- t — thickness in mm
- d — source-to-film distance in m
- A — activity in Ci
The 1.42 density exponent and the 1.4 thickness exponent are empirical: they reproduce the response of common industrial films, not a physical law. Confirm the result with a test exposure before the actual part.
Indicative film factors
Indicative values — calibrate them against your films, screen and target density.
| Film / system | Factor |
|---|---|
| Agfa T200 / D5 | 2 |
| Kodak MX125 / D4 | 4 |
| Fuji M100 / D3 | 5.4 |
Indicative result — check it against your authorisation and your dosimetry.