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Decay-in-storage calculator
Pick the isotope and the date the container was sealed to get the earliest date it can be surveyed for disposal.
Runs in your browser. Nothing you enter is sent or saved.
The rule
10 CFR 35.92 lets licensees hold waste for decay-in-storage only if the half-life is 120 days or less. Before disposal:
- survey the waste at its surface with a survey meter on its most sensitive scale and no shielding, and confirm it's indistinguishable from background;
- remove or deface all radiation labels;
- keep a record of each disposal for 3 years (10 CFR 35.2092).
Holding for 10 half-lives is a common licensing practice and rule of thumb, not the rule itself. The survey decides. Some licenses and states set their own minimum, so adjust "Minimum half-lives" to match yours.
Questions
Why 10 half-lives?
After 10 half-lives, 2−10 = 1/1024 of the activity remains (under 0.1%). For most short-lived medical waste, that's well below what a survey meter can tell apart from background.
Can CurieLedger keep our decay-in-storage log?
Yes. Premium tracks every container, its release date, the background survey and the disposal record. See plans.