Radiography
Radioactive source decay
Current activity from the assay activity and the time since the assay, or how long until the source falls to a given activity.
For reference only — verify against your procedure and the governing code.
1 Ci = 37 GBq exactly.
How long from the assay until the source decays to this activity.
Result
- Elapsed
- 30days
- Fraction remaining
- 75.45 %
- Activity now
- 2,792GBq
Formula
- A = A₀ · (1/2)^(t / T½)
- t = T½ · log₂(A₀ / A)
Units. Activity in GBq (metric) or Ci (imperial); 1 Ci = 37 GBq exactly. The decay fraction is a ratio, so the half-life arithmetic is the same in either.
Assumptions and limits
- Half-lives are the LNHB/DDEP recommended values: Ir-192 73.827 d, Co-60 5.2711 years (1,925.3 d), Se-75 119.781 d, Yb-169 32.018 d.
- Dates are counted as whole calendar days. The source certificate's assay activity and date govern.
Sources
- LNHB/DDEP, Table de Radionucléides (Decay Data Evaluation Project), section 2 "Nuclear Data" for Ir-192, Co-60, Se-75 and Yb-169 — recommended half-lives.
More radiography calculators
For reference only — verify against your procedure and the governing code.
Standards and documents are cited by their publishers' names to identify them. TRACE is not affiliated with, endorsed by or sponsored by ASTM International, ASME, the U.S. Nuclear Regulatory Commission, NIST or the Laboratoire National Henri Becquerel. Formulas are paraphrased and cited by clause; get the documents themselves from their publishers.