Calculators / Dose and shielding
Ir-192 radiography: dose rate, distance and shielding
Ir-192 is the workhorse of industrial radiography. Its spectrum is 28 lines from 61.5 to 1,061 keV, strongest at 316.506 keV, so a single-energy estimate misses part of the dose. The table sums all of them.
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- EXPOSURE, 1 Ci @ 1 m
- 462 mR/h
- H*(10), 100 Ci @ 1 m
- 516 mSv/h
- TUNGSTEN HVL (BROAD)
- 0.214 cm
- LEAD HVL (BROAD)
- 0.288 cm
A 100 Ci (3.7 TBq) source, unshielded
| DISTANCE | H*(10) | EXPOSURE |
|---|---|---|
| 1 m | 516 mSv/h | 46.2 R/h |
| 3 m | 57.4 mSv/h | 5.13 R/h |
| 10 m | 5.16 mSv/h | 462 mR/h |
| 30 m | 574 µSv/h | 51.3 mR/h |
| 50 m | 207 µSv/h | 18.5 mR/h |
| 100 m | 51.6 µSv/h | 4.62 mR/h |
The rate falls to 1 mSv/h at 22.7 m and to 20 µSv/h (2 mrem/h) at 161 m by the inverse-square law alone. With the app’s air option on — attenuation plus air scatter from the ANSI/ANS-6.4.3 air buildup factor — the 20 µSv/h distance is 147 m.
Shielding
| MATERIAL | HVL BROAD | TVL BROAD |
|---|---|---|
| Lead | 0.288 cm | 1.12 cm |
| Tungsten | 0.214 cm | 0.808 cm |
| Steel (iron) | 2.25 cm | 5.56 cm |
| Concrete | 10.1 cm | 21.5 cm |
| Water | 27.6 cm | 52.8 cm |
Assumptions
- Air. The table is for a vacuum path, as published dose constants are. In open air, attenuation and scatter nearly cancel to about 60 m for Ir-192’s spectrum; at 161 m the air option gives 79 % of the vacuum rate. Removing air attenuation alone, without the scatter it returns, would understate the dose there about 6×. Ground scatter is not modelled; surveying the boundary is what establishes it.
- Point source, no collimator or guide tube, no self-absorption in the capsule. Photons below 20 keV are excluded (Γδ).
- Nothing here replaces the survey and posting requirements of your licence.
Sources
- Gamma lines: IAEA decay_rads (ENSDF). Attenuation: NIST SRD 126.
- Buildup: ANSI/ANS-6.4.3 (Trubey, NUREG/CR-5740, 1991), with μ without coherent scattering from NIST XCOM. Air: the same standard's air buildup. H*(10): ICRP 74 Table A.21.
Numbers on this page computed by the physics code of Nuclear Toolkit 1.4.1, the same code as the app. How it is checked.
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