Iridium-192 — Definition & NDT Use
A radioactive isotope commonly used as a radiation source in radiographic testing. Ir-192 has a half-life of 73.8 days and emits gamma rays suitable for radiography. It is preferred over cobalt-60 for thin-wall inspections and portable industrial radiography due to its higher density, allowing smaller source capsules. Ir-192 requires less shielding than Co-60 but more safety precautions than X-rays.
On the job, Iridium-192 sits between the procedure and the indication — its calibration record, serial number, and condition all flow into the inspection report and the audit trail. Radiation passes through the part and a dense region (more material, more attenuation) records as a lighter band on film or digital detector, while a void, lack of fusion, or porosity records as a darker area; an image quality indicator (IQI) verifies that the technique was sensitive enough to be trusted. Calibration certificates, condition logs, and traceable serial numbers are what make the difference between an instrument that shows a number and an instrument whose number stands up in court or in front of an auditor.
The instrument's inspection scope is set by its OEM specification, its current calibration certificate, and any customer-specific qualifications that have been logged against it; a Iridium-192 that is in calibration but unqualified for a customer's procedure is still off the job.
- Etymology / Origin
- Element 77 (Ir) named for Greek iris (rainbow) due to its colourful salts; the 192 isotope is the workhorse industrial gamma source.
- Formula
- Activity A(t) = A0 × e^(-λt); λ = ln(2)/T_half; half-life 73.83 days.
- Units
- Activity in Curies (Ci) or Becquerels (Bq); 1 Ci = 3.7e10 Bq.
- Typical Range
- Project source 50–100 Ci new; replaced when activity falls below ~30 Ci; effective energy 296–612 keV (mean 380 keV).
- Measured / Produced By
- Survey meter with isotope-specific dose rate at 1 m; activity verified against decay calculation.
- Code References
- 10 CFR 34 (industrial radiography licensing); ASME Section V Article 2 (RT); ISO 17636-1 (RT of welds)
- Worked Example
- 100 Ci source after 90 days: A = 100 × e^(-ln2 × 90 / 73.83) ≈ 42.8 Ci — exposure times scale by ~2.3× from new.
ASME Section V Article 2
Radiographic examination requirements (penetrameter selection, IQI, density).
ASTM E94 / E1742
Standard guide for radiographic examination and film handling.
ISO 17636-1 / -2
Radiographic testing of fusion welds — film and digital detector arrays.
10 CFR 34
NRC regulations on industrial radiography licensing and operating safety.
A frequent finding in audits is a iridium-192 marked "in-cal" on the spreadsheet but with a current condition (damaged cable, missing cap) that would have invalidated the calibration if checked physically.
What does "Iridium-192" mean in NDT?
A radioactive isotope commonly used as a radiation source in radiographic testing. Ir-192 has a half-life of 73.8 days and emits gamma rays suitable for radiography
Which standards govern the use of Iridium-192?
Iridium-192 is most often referenced under ASME Section V together with the relevant ASTM practice or the matching ISO standard for the method; the contract or purchase order will name the controlling document and edition for any specific job.
What other NDT concepts should I read alongside Iridium-192?
The most directly related entries in this glossary are "radiographic testing", "cobalt 60", "gamma ray"; reading those together gives you the surrounding vocabulary used in inspection reports and procedures.