BETA
Disclaimer: This tool is currently in beta. Features are actively being developed and tested, so you may encounter minor bugs or incomplete functionality.
Gamma Exposure Time Calculator

Gamma Exposure Time Calculator

Input your source details, material, and film setup to calculate accurate exposure times.

Setup Parameters

mm
mm

Calculated Exposure Time

Define Inputs...

Single Film Timer

Spacer

00:00

Double Film Timer

+10-20% time for superimposed

00:00
Live Mathematical Formula
T = (-- × --²) × 2(-- / --) / (-- × --)
= -- mins

Recent Exposures

Radiography Reference Guide

Physics Engine

Calculates total photon dose needed at the physical film plane, negating manual sliding rules.

Hrs = [ FF × SFDm² × 2(x/HVL) ] / [ A × Γ ]

  • FF (Film Factor): Roentgens needed to achieve the target density.
  • SFDm: Distance in meters (Inverse Square Law).
  • 2(x/HVL): Continuous exponential attenuation.
  • A & Γ: Source Activity (Ci) and Gamma Constant.

Isotopes (Γ)

The intrinsic radiation output (R·m²/hr·Ci).

  • Ir-192 (Γ = 0.48)
    Standard. Steel 12-63mm. Avg ~380 keV.
  • Se-75 (Γ = 0.203)
    Thin wall pipe. Smaller barricades. Avg ~220 keV.
  • Co-60 (Γ = 1.30)
    Heavy castings/concrete. Avg ~1.25 MeV.

Film Classes

Finer grain yields higher detail but demands exponentially more dose.

Class 1 (Ultra Fine) D2/D3/M100. High detail.
Class 2 (Fine Grain) D4/D5/MX125. General code.
Class 3 (Medium) D7/AA400. Fast speed.

Density: Typically 2.0 to 4.0. Adjusting density multiplies the base required Roentgens linearly.

Disclaimer: This tool provides estimated exposure times based on absolute mathematical physical models. Results should always be verified against official source certificates, standard operating procedures, and authorized slide rules. Do not rely solely on these calculations for safety or compliance operations.

HVL Reference (mm)

HVL: Thickness required to absorb 50% of the radiation dose.

Steel (Carbon)

Se-75
11.0
Ir-192
13.0
Co-60
21.0

Aluminum

Se-75
22.0
Ir-192
33.0
Co-60
60.0

Concrete

Se-75
33.0
Ir-192
43.0
Co-60
61.0

Lead

Se-75
2.0
Ir-192
4.8
Co-60
12.5

Film Equivalency

Factor (FF): Base Roentgens required to hit an optical density of 2.0.

High Speed

FF: 0.4
Kodak
HS800
Agfa
D8
Fuji
IX150

Medium Speed

FF: 0.8
Kodak
AA400
Agfa
D7
Fuji
IX100

Fine Grain

FF: 1.6
Kodak
T200
Agfa
D5
Fuji
IX80

Fine Grain (Slow)

FF: 2.4
Kodak
MX125
Agfa
D4
Fuji
IX50

Ultra Fine

FF: 4.0
Kodak
M100
Agfa
D3
Fuji
IX30

Extreme Fine

FF: 6.4
Kodak
DR50
Agfa
D2
Fuji
IX25

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