https://en.wikipedia.org/wiki/Kramatorsk_radiological_accident#:~:text=The%20Kramatorsk%20radiological%20accident%20was,rate%20of%201800%20R%2Fyear.

TheKramatorsk radiological accidentwas aradiation accidentthat happened inKramatorsk, in theUkrainian SSRfrom 1980 to 1989. A small capsule containing highly radioactivecaesium-137was found inside the concrete wall of an apartment building, with a surface gamma radiation exposure dose rate of 1800R/year.^[1]The capsule was detected only after residents requested that the level of radiation in the apartment be measured by a health physicist.^[1]

The capsule was originally part of a radiation level gauge and was lost in the Karansky quarry in the late 1970s. The search for the capsule was unsuccessful and ended after a week. The gravel from the quarry was used in construction.^[2]The caesium capsule ended up in the concrete panel of apartment 85 of building 7 on Mariyi Pryimachenk Street (at the time under the Soviet name Gvardeytsiv Kantemirovtsiv), between apartments…