A source no longer under any regulatory control, whether abandoned in a closed clinic, lost from a radiography truck, stolen or mixed into scrap metal. Orphan sources have caused fatal radiation injuries and costly contamination when people unaware of the danger opened them, most notoriously at Goiania. Portal monitors at scrapyards and steel mills, national source registries and secure end-of-life return programmes exist to find and prevent them.
Scrapyard portal alarmed on a truck, likely an orphan source in the load, isolate it and call the regulator.
Related terms
Sealed source
Radioactive material permanently sealed in a capsule so it cannot escape under normal use.
Deterministic effects
Radiation injuries that appear only above a threshold dose and become more severe as dose increases.
Pig
A heavy lead or tungsten container used to store or carry a radioactive source or sample.
Curie
The non-SI unit of radioactivity, equal to 37 billion decays per second.