Between March and July 1962, a radiation incident in Mexico City occurred when a ten-year-old boy took home an industrial radiography source that was not contained in its proper shielding. Five individuals received significant overdoses of radiation from the 200-gigabecquerel cobalt-60 capsule,^[1] four of whom died.^[2]

Reports differ as to the source's provenance: it was either found in a dump,^[3] found in a field,^[4] or was already in the house's yard when the affected family moved in and "was left to the family to keep and watch without any of the members of the family knowing exactly what the container was".^[5] A 2008 report by UNSCEAR says it was left, unprotected, in the yard by an engineer.^[1]

The boy is believed to have obtained the source some time after moving into the house on March 21. He kept it in his trouser pocket for several days. On April 1, his mother placed it in the kitchen cabinet of their home, where it remained until July 22. The boy died on April 29. Subsequently, his mother – six months pregnant at the time – died on July 19; his two-year-old sister died on August 18; and his paternal grandmother, who had been living with the family since April 17, died on October 15 that year.^[5] The boy's father also received a significant radiation dose; although he was left permanently sterile,^[1] he survived, presumably because he worked outside the home and his exposure was lower.^[6][7][8]